Conversational Linux
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Conversational Linux for the Windows User
Copyright Jonathan Roper [email protected]
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About the Author Joe Roper Has had a commercial and operational background in the transport industry before moving into IT in the mid nineties, and into communications in the late nineties. Joe is one of the three lead developers with PBX in a Flash together with Ward Mundy and Tom King, both of whom have contributed to this document. Joe is also the Commercial Director or A2Billing. www.a2billing.net. A2Billing, licensed under the GPL, when combined with Asterisk is a physical Telecom Platform and Soft-Switch providing a wide range of telecoms services using either traditional telephone technology or VoIP. It contains a real-time billing engine which rates and bills and invoices calls, and contains a payment gateway. Joe is available for consultancy, Googling on "joe roper"+voip or "joe roper"+wireless will show some of the projects that Joe has been involved in, which may help establish his credentials. This document is offered in the hope that it may be useful, but no warranty for the accuracy of the document is either implied or given. Please pass on errors and suggestions for improvement on to [email protected] This document is released under the creative commons license – Attribution share. See http://creativecommons.org/licenses/by-sa/3.0/legalcode This license lets you remix, tweak, and build upon this work even for commercial reasons, as long as you credit Joe Roper and license your new creations under the identical terms. This license is often compared to open source software licenses. All new works based on yours will need to carry the same license, so any derivatives will also allow commercial use.
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Table of Contents
1
About the Author...........................................................................................................................................2
2
Table of Contents...........................................................................................................................................3
3
Introduction....................................................................................................................................................7
4
Open Source ...................................................................................................................................................7
5
4.1
What is Open Source ..............................................................................................................................8
4.2
Can I modify the software?.....................................................................................................................8
4.3
I want to make a Business and sell OSS based products. .....................................................................8
4.4
Can I Sell a Modified Version? ..............................................................................................................9
4.5
I’ve written a killer App for the product; do I need to give it away?....................................................9
4.6
So how do I make money? ....................................................................................................................10
Preparation...................................................................................................................................................10 5.1 Virtual Machine ....................................................................................................................................10 5.1.1 VMware........................................................................................................................................10 5.1.2 Microsoft Virtual PC....................................................................................................................11
6
5.2
Hardware ..............................................................................................................................................11
5.3
PuTTY....................................................................................................................................................12
5.4
WinSCP .................................................................................................................................................12
Installation of ISO .......................................................................................................................................13 6.1
Burning the ISO ....................................................................................................................................13
6.2
Installation preparation (Hardware)...................................................................................................14
6.3
Installation (vmware)............................................................................................................................14
7
Webmin.........................................................................................................................................................14
8
Linux for PBX systems ...............................................................................................................................15
9
8.1
Concept of Linux...................................................................................................................................15
8.2
Why CentOS ..........................................................................................................................................15
8.3
The Command Line...............................................................................................................................16
8.4
GUI – startx...........................................................................................................................................16
8.5
Accessing the System ............................................................................................................................17
8.6
SSH and Putty .......................................................................................................................................17
8.7
SSH and WinSCP..................................................................................................................................18
8.8
SSH ........................................................................................................................................................20
8.9
SCP ........................................................................................................................................................20
Linux Filesystem..........................................................................................................................................20 9.1
Linux File System Explained ................................................................................................................21
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9.2 Directories.............................................................................................................................................22 9.2.1 /sbin...............................................................................................................................................22 9.2.2 /bin ................................................................................................................................................22 9.2.3 /boot ..............................................................................................................................................22 9.2.4 /dev................................................................................................................................................22 9.2.5 /etc.................................................................................................................................................23 9.2.6 /home ............................................................................................................................................23 9.2.7 /lib .................................................................................................................................................23 9.2.8 /lost+found....................................................................................................................................23 9.2.9 /mnt ...............................................................................................................................................24 9.2.10 /opt ................................................................................................................................................24 9.2.11 /proc ..............................................................................................................................................24 9.2.12 /root...............................................................................................................................................24 9.2.13 /tmp ...............................................................................................................................................24 9.2.14 /usr.................................................................................................................................................24 9.2.15 /var ................................................................................................................................................25 10
Command Line Construction................................................................................................................25 10.1 Where to get help ..................................................................................................................................25 10.1.1 --help or --h...................................................................................................................................25 10.1.2 man <>.....................................................................................................................25 10.1.3 apropos <>.................................................................................................................25 10.1.4 whatis <>...................................................................................................................26 10.1.5 tab key...........................................................................................................................................26
11
Filesystem Navigation and Commands................................................................................................26 11.1
# ls..........................................................................................................................................................26
11.2
# cd.........................................................................................................................................................26
11.3
# pwd .....................................................................................................................................................26
11.4
# cp.........................................................................................................................................................26
11.5
# mv........................................................................................................................................................26
11.6
# mkdir...................................................................................................................................................27
11.7
# find......................................................................................................................................................27
11.8
# grep.....................................................................................................................................................27
11.9
# rm........................................................................................................................................................27
11.10
# touch...............................................................................................................................................27
11.11
Links / shortcuts................................................................................................................................27
11.12
# wget ................................................................................................................................................27
12
Disk Usage ................................................................................................................................................28 12.1
# du ........................................................................................................................................................28
12.2
# df .........................................................................................................................................................28
13
Editing and reading files ........................................................................................................................28 13.1
Nano ......................................................................................................................................................29
13.2
WinSCP .................................................................................................................................................29
13.3
# cat .......................................................................................................................................................29
13.4
# less ......................................................................................................................................................29
13.5
# tail.......................................................................................................................................................29
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13.6 14
# head ....................................................................................................................................................29 File Ownership and permissions...........................................................................................................29
14.1
The Basics .............................................................................................................................................29
14.2
Chmod ...................................................................................................................................................30
14.3
Chown....................................................................................................................................................31
14.4
chgrp......................................................................................................................................................31
15
Services .....................................................................................................................................................31 15.1
# chkconfig ............................................................................................................................................32
15.2
/etc/rc.d/rc.local ....................................................................................................................................32
15.3
Stopping services and processes. .........................................................................................................32
15.4
# ps aux..................................................................................................................................................33
15.5
# kill .......................................................................................................................................................33
15.6
# kill -9...................................................................................................................................................33
15.7
# top .......................................................................................................................................................33
16
Reboot and shutdown.............................................................................................................................33 16.1
# reboot..................................................................................................................................................33
16.2
# shutdown –h now ...............................................................................................................................33
17
Pipe............................................................................................................................................................34 17.1
# | ...........................................................................................................................................................34
17.2
Redirect Output.....................................................................................................................................34
17.3
# >..........................................................................................................................................................34
17.4
## >>.....................................................................................................................................................34
18
Compression ............................................................................................................................................34 18.1
# tar........................................................................................................................................................35
18.2
# gzip......................................................................................................................................................35
18.3
# bzip......................................................................................................................................................35
18.4
# zip & unzip .........................................................................................................................................35
19
Networking...............................................................................................................................................36 19.1
# ifconfig................................................................................................................................................36
19.2
# system-config-network.......................................................................................................................36
19.3
# resolv.conf ..........................................................................................................................................36
19.4
# hostname.............................................................................................................................................37
19.5
# ifdown .................................................................................................................................................37
19.6
# ifup......................................................................................................................................................37
19.7
# ping .....................................................................................................................................................37
19.8
# traceroute ...........................................................................................................................................37
19.9
# mtr.......................................................................................................................................................37
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Network Security.....................................................................................................................................37 20.1.1
21
Iptables..........................................................................................................................................37
Installing software...................................................................................................................................38 21.1 Compiling from source .........................................................................................................................38 21.1.1 # make clean.................................................................................................................................38 21.1.2 # ./configure..................................................................................................................................38 21.1.3 # make...........................................................................................................................................38 21.1.4 # make install................................................................................................................................38 21.2
# yum .....................................................................................................................................................38
21.3
# rpm......................................................................................................................................................39
22
Logs ...........................................................................................................................................................39 22.1
/var/log/messages..................................................................................................................................39
22.2
/var/log/dmesg.......................................................................................................................................39
22.3
/var/log/asterisk/full ..............................................................................................................................39
22.4
# logrotate .............................................................................................................................................40
23
Crontab.....................................................................................................................................................40
24
Users and Groups....................................................................................................................................40 24.1
Users......................................................................................................................................................40
24.2
Groups...................................................................................................................................................40
24.3
# sudo.....................................................................................................................................................40
25
Network Services.....................................................................................................................................41 25.1
NTP........................................................................................................................................................41
25.2
DNS........................................................................................................................................................41
25.3
DHCP ....................................................................................................................................................42
25.4 TFTP......................................................................................................................................................42 25.4.1 Option 66......................................................................................................................................42 25.5
Sendmail / Postfix..................................................................................................................................42
25.6
Apache...................................................................................................................................................42
25.7
PHP .......................................................................................................................................................43
25.8
MySQL...................................................................................................................................................43
26
Hardware..................................................................................................................................................43 26.1
# lspci....................................................................................................................................................43
26.2
# cat /proc/interrupts ............................................................................................................................43
27
28
SSH Tunnelling........................................................................................................................................43 27.1
Example One.........................................................................................................................................44
27.2
Example Two.........................................................................................................................................44 Conclusion................................................................................................................................................45
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Introduction The purpose of the manual is to explain some basic commands for Linux to the Windows user, to give them confidence to use Linux. Linux, in the PBX environment does not usually have a graphical user interface. However even if it did, it would be more complicated to explain that then to simply use the command line interface. Linux differs from Windows in that a range of windows Managers and graphical user interfaces can be used, the most popular of which are Gnome and KDE. The following sections should give some techniques that the user, more familiar with Windows, can use to manage and configure their PBX system. This manual concentrates on the CentOS (Community Enterprise Operating System) as this is one of the most widely used in PBX deployments. It is based on Red Hat Enterprise Linux (RHEL) and is supported for seven years after release. By the time you have practiced the commands in this manual, you should have “Conversational Linux”
4
Open Source There has been an explosion and growth of open source software in the last few years, especially in the telecoms market. Open Source software in many cases is every bit as good as the commercial equivalent. The first thing to understand is that Open Source Licensing is in no way anti-commercial. OSS software is, and always has been commercial. What it is, is Anti Lock in. For your customers, OSS is a huge selling point. They will always be able to get support for their product, even if they do not buy it from you. If you do a good job, then of course they will have no reason to move.
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4.1 What is Open Source Open Source software is software that is released under a license that allows you to modify the program to suit yourself. Open Source is generally but not always free of charge. Open Source software used to be called Free Software. The Free in the name DID NOT refer to the price, but to the Freedom to modify and alter the program. One of the most popular licenses is GPL v2 – http://www.gnu.org/licenses/old-licenses/gpl-2.0.html. There is a GPL v3, but this has not been widely adopted as yet. The idea with OSS software is that you can contribute to the development of the product, and enjoy the fruits of your labour. The code can be inspected by your peers, and commented about publicly. This concentrates the mind to do it properly. A worthwhile read is the Beekeeper analogy http://wiki.pentaho.org/display/BEEKEEPER/The+Beekeeper The advice below is based opinion, and before making commercial decisions based on this advice, you would be advised to do your own research.
4.2 Can I modify the software? If the software is for your own use, you can do whatever you want with it. There are no restrictions of any note. However, if you are going to re-distribute or sell your software, read on. It is a good idea to return your modifications back to the community for inclusion in future releases. In this way, when a new feature is added, you may not have to re-apply your modifications, and the product gets ever better. Remember that the copyright is still held by the original developer, so if you take a script, copy it, and pass it off as your own, and place your own copyright on it, that is illegal, and morally wrong.
4.3 I want to make a Business and sell OSS based products. You may redistribute GPL software, and indeed you may make a charge for the software. You must give the same rights to your customers as you have received from the original distributor of the OSS software. So given that you have the right to modify the
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software, so does your customer. They also have the right to redistribute the software as well. You can make more money by adding other elements to the sale, such as hardware, guarantees, training, and support
4.4 Can I Sell a Modified Version? Yes, you can make modifications to the software. However, any changes that you make to the software must be clearly marked and commented. If you make a mistake and break something, the reputations of the original developers should not be affected.(Section 2a of the GPL) Additionally, under the terms of the GPL, you must make your modifications freely (as in make no charge) available to any and all third parties, e.g. post a link to it on your website. (Section 2b of the GPL) So you can re-brand as your own? The basic tenant of Copyright law is that it gives the copyright holder the right to be credited for the work. In order to be sure, you would need to take legal advice, or simply ask permission of the copyright holder. The copyright law is nothing to do with the GPL. However, it is good manners, and a good strategy to talk to the original developers to get them to provide or give permissions fort a re-branded system, for which they make a charge which goes to support the project, and of course, updates and changes to the original code are unlikely to break your customised copy, and of course you stay in the development loop.
4.5 I’ve written a killer App for the product; do I need to give it away? You may write an application or modification to the product, but do not want to release the code as it gives you a competitive advantage. The answer to this is a little more grey, and to a great degree, depends on your moral radar’ A suggested guideline is that if you have to modify the original released code in order to make your application work, then your work will have to fall under the GPL. If you do not release the code to the GPL, then you could be in breach of the license, and lose the right to use the product. (Section 4 of the GPL) If the code communicates at arms length from the original code, then that is acceptable. (Read Section 2c carefully)
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4.6 So how do I make money? Providers of OSS software want you to make money from their work. That’s the point. Of course they would also like money and receive help as well. There are a number of ways that both the provider of the OSS software and the reseller can make money from OSS. 1. If the code is an original work, licensed under the GPL, then the developers and project owners may make a charge for the software. The purchaser of the software can resell the software if they wish, or indeed give it away if they so desire. After all, they still own the copyright. 2. Sell installation services, support and guarantees with the product, See Digium as an example of this. 3. Provide other Value Add Services, e.g. minutes and DID for PBX services. 4. Provide and sell documentation for the project. 5. Provide a service for updating and fixing the product. 5
Preparation To work through the exercises below, a test machine is required, virtual or real, as well as some useful tools to be downloaded from the internet. An internet connection is also required.
5.1 Virtual Machine A virtual machine is a program that allows operating systems to run in a window on a Windows, Linux or Mac PC. For the purposes of this manual, we will be concentrating on Windows. Note that it is not generally possible to run a production PBX on a virtual PC or server. Installing a virtual machine on a PC will not affect any existing data on the server. 5.1.1 VMware VMware from, www.vmware.com is one of the most popular virtual environments, as it supports all the major operating systems.
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In our case we only need VMware player, which will play an existing VMware image. VMware player is free of charge, but you do have to register to download it. You will need a VMware hard disk, and the .vmx configuration file. The .vmx file controls the attributes of the virtual machine, such as the memory, presence of network interfaces, the CDRom etc. It is a text file can be edited with notepad or wordpad. There is a blank hard disk and basic configuration file available from: http://www.pbxinaflash.com/downloads/pbxinaflash.zip
Alternatively, you can upgrade to VMware server, which has a cost, to create your own VMware disks. There is also a free open source program called VMX Builder, which will allow you to create your own hard disks and machine configurations. This can be found at: http://petruska.stardock.net/software/VMware.html 5.1.2 Microsoft Virtual PC There is another virtual machine program available to you called Virtual PC, which is a free download from Microsoft. This is available from:http://www.microsoft.com/windows/products/winfamily/virtu alpc/default.mspx For server grade hardware, Microsoft Virtual Server is also available. During the installation of Microsoft Virtual PC, there may be warnings about the operating system not being compatible. This is the case with Windows XP home edition. Note the warnings and continue with the install. There seem to be no side effects to installing VPC with Windows XP, despite the warnings.
5.2 Hardware Almost any hardware will do to run Linux on. Bear in mind that most Linux installs will delete any data on the PC, so do not install your main machine.
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Hardware that should be excluded with CentOS 5, the OS we will be using for this manual, is anything with an i586 architecture, as this is not supported. An example of this hardware would be a Via EPIA C3 processor. 10Gb is more than sufficient for the hard drive. 256Mb of RAM or more is recommended. Motherboards with onboard LAN may or may not be supported. It has been noted that Nvidia chipsets do have problems recognising the LAN, so it may be necessary to buy a network card to circumvent this problem. It will only be a matter of time before CentOS provides the drivers for more modern hardware. The advice is to research the motherboard on the internet to see if there are likely to be any compatibility problems.
5.3 PuTTY PuTTY is a windows program used to remote manage Linux machines from the command line. It gives a window onto the Linux machine, and any commands typed into the Putty window are executed on the remote machine. Putty is available from http://www.chiark.greenend.org.uk/~sgtatham/putty/ It is one executable file, so it can be run from a Windows desktop without needing to install it on the machine. It can be simply deleted afterwards if you are on a guest on some else’s machine. Putty is free of charge
5.4 WinSCP WinSCP is a program similar to Windows Explorer. It is a good program for those more used to Windows than they are to the command line. It allows drag and drop copying to and from the desktop, as well as changing permissions on files, editing files, and running non interactive commands. WinSCP is available from http://winscp.net/eng/index.php
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Note that this program is installed into Windows, so it may not be suitable for installing on a guest PC. WinSCP is free of charge 6
Installation of ISO One can download the ISO’s prepared by the various PBX aggregators such as PBX in a Flash, or CentOS can be downloaded from the CentOS website. There are ISO images on DVD and CD for many different computer architectures. The one we will most likely to be interested in is the i386 architecture. However, modern hardware and processors often support 64bit operating systems, so you may also wish to try the x86_64 download as well, which will make full use of the architecture and 64 bit capabilities. 64 bit machines can address far more memory. Typically, 32 bit architecture can only address up to 4Gb of memory, whereas 64 bit can address considerably more. Any more than 4Gb of memory on a 32 bit operating system is a waste of money, unless a special kernel is compiled.
6.1 Burning the ISO When the ISO has been downloaded e.g. pbxinaflash.iso it needs to be burnt to a CD. An ISO image is an image of the disk, which tells the CD burner where to put the relevant files and directories. It is not sufficient to simply copy the ISO onto the CD, it needs to be burnt properly. The usual, most popular tool to do this is Nero. This program is often bundled with PC’s from OEM distributors. Depending on the version, look for “Burn CD image” If Nero is not available, then there is a Windows power toy available from http://isorecorder.alexfeinman.com/isorecorder.htm which will burn an ISO image onto CD.
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Note that on virtual machines, it is not necessary to burn the ISO to a physical CD, as the VM image allows you to mount the ISO image as if it was a physical CD.
6.2 Installation preparation (Hardware) The first job is to make the machine bootable from the CDROM drive. Hardware varies, but in most cases it is necessary to enter the BIOS, often by pressing F2, or del during the initial boot up. Once the BIOS is open, then the boot order can be altered so it boots from CD first, and then the hard drive. In other cases, it may be necessary to press a key combination to enter the boot options, e.g. F12. This allows you to select the boot device. Chose CDROM. For machines without a CDROM, a USB CDROM drive may have to be purchased, and a modern PC should boot from a USB interface. This may not be the case with older machines. Ensure that all data that you want to keep has been backed up. To check that the CD is in good order, then at the boot of the CD, type linux mediacheck.
6.3 Installation (vmware) On a fresh virtual machine, there will be no requirement to do any preparation apart from to ensure that the ISO image is in the right place relative to the VM image. For VMware, open the .vmx file and find the line which points to the ISO e.g. ide0:1.fileName = "c:\ippbx\concordiax.iso" Ensure it points to the filename of the ISO image. In Microsoft VPC, simply check the properties and options. Future installations over the top of existing installs will require you to bring up the boot order menu. In VMware, press escape as the system boots. Be quick or you will miss it. 7
Webmin Webmin is the swiss army knife of Linux administration for the Linux Conversational. It simplifies changes to be made to the system. It allows the configuration of Linux though a web based UI, which runs separately in its own process.
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Webmin is a web based application. By default, it is installed on port 10,000 however that port is sometimes changed for security. E.g. PiaF puts Webmin on 9001. To access Webmin, type the URL of your server appended with “:10000” e.g. http://myserver.com:10000 or in some cases https://myserver.com:10000 If Webmin is installed after the operating system, the password is usually the same as the root password. However, if it is installed with the OS, then the password has to be set separately. 8
Linux for PBX systems
8.1 Concept of Linux Linux is based on Unix which is a very mature operating system. Linux is known to be very robust, and suits “always on” applications as it can be run for many years without needing a reboot. The stability is maintained by the mindset of most Linux developers. Most Linux programs only do one thing, but do it really well. The make up of most operating systems is based on a layered model, and programs and functions only talk to their direct neighbours. E.G. -
Hardware talks to the Kernel The Kernel talks to applications.
In this way the kernel knows all about the hardware in a machine, and does not allow applications to talk directly to the hardware, which may cause a conflict. Thus, whenever new hardware is added, it may be necessary to recompile the kernel, or compile the hardware drivers against the kernel so that they know how to interact with each other.
8.2 Why CentOS A quick Google will throw up a lot of Linux distributions which have their own positives and negatives. People are as loyal to their particular distribution as they are to their football team.
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There are advantages and disadvantages to them all, but, a choice as to be made, in this case, CentOS has been chosen. CentOS is Redhat Linux with all the branding taken out. RHEL is not usually available free of charge, and requires an annual support fee, and as such, has lots of paid developers working on the system. Not surprisingly, this allows it to spend more money on the development and support of hardware, and has been adopted as the defacto distribution for servers. Fedora Core is the hairy bleeding edge of RHEL. Older versions of Fedora Core cascade into RHEL, which in turn is released as CentOS. CentOS is distributed completely free of charge, and is licensed under the GPL. The reasons for choosing Centos, is that enjoys the same benefits of RHEL. RHEL updates are usually ported into CentOS within 72 hours of them becoming available. CentOS is maintained for seven years after release, so the current 5.1 release is set to be supported until 2014. A side benefit is that if you were to ever release a PBX where the customer wanted to have some guarantees about the stability, a PBX could easily be built using RHEL and Asterisk Business Edition. For more information on Centos, see www.centos.org
8.3 The Command Line With a PBX install, it is not usually necessary to spend too long at the command line. Only long enough to configure the hardware, software and network and do any trouble shooting that may be required. After this time, most configurations are done via web pages.
8.4 GUI – startx Graphical user interfaces (also known as X) can be installed to CentOS, and there are a few choices. However, GUI’s are rarely installed on Servers, as servers are rarely touched once installed. GUI’s use quite a lot OS system resources. If no one is looking at the GUI, then there is no point in one being present.
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Having said that, the amount of resources required to run a GUI on a modern server is only a small percentage of the available power. If a GUI has been installed, then it can be started with the command startx. When you have finished with the GUI, it can be stopped with the key combination CTRL-ALT-BACKSPACE.
8.5 Accessing the System The main method of accessing the server is via a protocol called SSH. Secure Shell. The commands and screen output is encrypted, so it is a secure method of connecting. SSH is a TCP connection on port 22. For a public server, this may need to be changed to a non standard port.
8.6 SSH and Putty To access the command line from Windows, PuTTY has to be launched. It will bring up a screen as below:-
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Simply fill in the IP address or hostname and click open.
You will then be prompted for the username - usually root, press enter, then type the password. As you are typing the password, there will be no screen output, so just keep typing and press enter. If authenticated properly, then you will end up in your home directory. In the case of root, you will be in the /root directory When first connecting to a Linux machine, you will get a prompt if you have never connected before. Accept this prompt. If you have connected to the machine before and you get this prompt, and then ensure that you have not been redirected to another machine. To copy a command from the Windows desktop, right click and copy the text, click in the Putty window and right click. This will paste the contents of the clipboard into the remote machine at the command prompt. To copy from the Putty window, simply highlight the text to be copied. This places the text on the windows clipboard. Right click to paste the text at the command prompt, or paste the contents into another Windows application
8.7 SSH and WinSCP WinSCP is a program which gives you a window onto the remote machine.
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WinSCP also comes with its own internal text editor.
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8.8 SSH It is possible to ssh from one Linux machine to another. Simply type ssh ipaddress or ssh root@ipaddress.
8.9 SCP Secure copy. Copy a file. Using the SCP protocol, copy files from one Linux machine to another.
9
Linux Filesystem The Linux file system has a number of partitions. At its most simple, it contains three partitions: -
-
The boot partition – this contains the mechanism to boot the system. The Swap partition – This is where stuff held in RAM is shifted to the hard drive, which pretends to be RAM, albeit, very much slower. The main file system – this contains the files and folders as well as applications.
There is no need to worry about this too much. For the moment, just go with the options offered to your doing the install.
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9.1 Linux File System Explained Original article by Mayank Sarup [email protected] Posted: (2001-01-03 10:08:44 EST http://www.freeos.com/articles/3102 )
The first thing that most new users shifting from Windows will find confusing is navigating the Linux file system. The Linux file system does things a lot more differently than the Windows file system. This article explains the differences and takes you through the layout of the Linux file system. For starters, there is only a single hierarchal directory structure. Everything starts from the root directory, represented by '/', and then expands into sub-directories. Where DOS/Windows had various partitions and then directories under those partitions, Linux places all the partitions under the root directory by 'mounting' them under specific directories. Closest to root under Windows would be c:. Under Windows, the various partitions are detected at boot and assigned a drive letter. Under Linux, unless you mount a partition or a device, the system does not know of the existence of that partition or device. This might not seem to be the easiest way to provide access to your partitions or devices but it offers great flexibility. This kind of layout, known as the unified file system, does offer several advantages over the approach that Windows uses. Let's take the example of the /usr directory. This directory off the root directory contains most of the system executables. With the Linux file system, you can choose to mount it off another partition or even off another machine over the network. The underlying system will not know the difference because /usr appears to be a local directory that is part of the local directory structure! How many times have you wished to move around executables and data under Windows, only to run into registry and system errors? Try moving c:/windows/system to another partition or drive. (No; Don't!!!) Another point likely to confuse new users is the use of the frontslash '/' instead of the backslash '' as in DOS/Windows. So c:\windows\system would be /c/windows/system. Well, Linux is not going against convention here. Unix has been around a lot longer than Windows and was the standard a lot before Windows was. Rather, DOS took the different path, using '/' for command-line options and “\” as the directory separator.
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To liven up matters even more, Linux also chooses to be case sensitive. What this means that the case, whether in capitals or not, of the characters becomes very important. So this is not the same as THIS or ThIs for that matter. This one feature probably causes the most problems for new users.
9.2 Directories We now move on to the layout or the directory structure of the Linux file system. Given below is the result of a 'ls -p' in the root directory. bin/ dev/ home/ lost+found/ proc/ sbin/ usr/ boot/ etc/ lib/ mnt/ root/ tmp/ var/ 9.2.1 /sbin This directory contains all the binaries that are essential to the working of the system. These include system administration as well as maintenance and hardware configuration programs. Find lilo, fdisk, init, ifconfig etc here. These are the essential programs that are required by all the users. Another directory that contains system binaries is /usr/sbin. This directory contains other binaries of use to the system administrator. This is where you will find the network daemons for your system along with other binaries that only the system administrator has access to, but which are not required for system maintenance, repair etc. 9.2.2 /bin In contrast to /sbin, the bin directory contains several useful commands that are used by both the system administrator as well as non-privileged users. This directory usually contains the shells like bash, csh etc. as well as much used commands like cp, mv, rm, cat, ls. There also is /usr/bin, which contains other user binaries. These binaries on the other hand are not essential for the user. The binaries in /bin however, a user cannot do without. 9.2.3 /boot This directory contains the system map file as well as the Linux kernel. Lilo places the boot sector backups in this directory. 9.2.4 /dev This is a very interesting directory that highlights one important characteristic of the Linux file system - everything is a file or a
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directory. Look through this directory and you should see hda1, hda2 etc, which represent the various partitions on the first master drive of the system. /dev/cdrom and /dev/fd0 represent your CDROM drive and your floppy drive. This may seem strange but it will make sense if you compare the characteristics of files to that of your hardware. Both can be read from and written to. Take /dev/dsp, for instance. This file represents your speaker device. So any data written to this file will be re-directed to your speaker. Try 'cat /etc/lilo.conf > /dev/dsp' and you should hear some sound on the speaker. That's the sound of your lilo.conf file! Similarly, sending data to and reading from /dev/ttyS0 ( COM 1 ) will allow you to communicate with a device attached there - your modem. 9.2.5 /etc This directory contains all the configuration files for your system. Your lilo.conf file lies in this directory as does hosts, resolv.conf and fstab. Under this directory will be X11 subdirectory which contains the configuration files for X. More importantly, the /etc/rc.d directory contains the system startup scripts. This is a good directory to backup often. It will definitely save you a lot of re-configuration later if you re-install or lose your current installation. 9.2.6 /home Linux is a multi-user environment so each user is also assigned a specific directory which is accessible only to them and the system administrator. These are the user home directories, which can be found under /home/username. This directory also contains the user specific settings for programs like IRC, X etc. 9.2.7 /lib This contains all the shared libraries that are required by system programs. Windows equivalent to a shared library would be a DLL file. 9.2.8 /lost+found Linux should always go through a proper shutdown. Sometimes your system might crash or a power failure might take the machine down. Either way, at the next boot, a lengthy file system check using fsck will be done. Fsck will go through the system and try to recover any corrupt files that it finds. The result of this recovery operation will be placed in this directory. The files recovered are not likely to be complete or make much
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sense but there always is a chance that something worthwhile is recovered. 9.2.9 /mnt This is a generic mount point under which you mount your file systems or devices. Mounting is the process by which you make a file system available to the system. After mounting your files will be accessible under the mount-point. This directory usually contains mount points or sub-directories where you mount your floppy and your CD. You can also create additional mountpoints here if you want. There is no limitation to creating a mount-point anywhere on your system but convention says that you do not litter your file system with mount-points. 9.2.10
/opt This directory contains all the software and add-on packages that are not part of the default installation. Generally you will find KDE and StarOffice here. Again, this directory is not used very often as it's mostly a standard in Unix installations.
9.2.11
/proc This is a special directory on your system that is a pseudo file system held in memory and tracks running processes on the machine. Most of the information is /proc is updated live to match the current state of the operating system.
9.2.12
/root We talked about user home directories earlier and well this one is the home directory of the user root. This is not to be confused with the system root, which is directory at the highest level in the file system.
9.2.13
/tmp This directory contains mostly files that are required temporarily. Many programs use this to create lock files and for temporary storage of data. On some systems, this directory is cleared out at boot or at shutdown.
9.2.14
/usr This is one of the most important directories in the system as it contains all the user binaries. X and its supporting libraries can be found here. User programs like telnet, ftp etc are also placed here. /usr/doc contains useful system documentation.
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/usr/src/linux contains the source code for the Linux kernel. If you are compiling programs from source such as Asterisk, you would put the source files under /usr/src 9.2.15
/var This directory contains spooling data like mail and also the output from the printer daemon. The system logs are also kept here in /var/log/messages. You will also find the database for BIND in /var/named and for NIS in /var/yp. This was a short and basic look at the Linux file system. You do need to have at least this basic knowledge of the layout of the file system to fully utilize its potential. One good place to read about the file system is this detailed document at www.pathname.com/fhs/1.2/fsstnd-toc.html that specifies the standard structure of the Linux file system.
10 Command Line Construction Most Linux commands are formed in the same way: Command – options Filename Below is a list of resources on the server to get information on a particular command.
10.1 Where to get help 10.1.1
--help or --h Typing a command followed with –help will generally give a quick aide memoire on the command
10.1.2
man <> man stands for Manual. Type man followed by the command line for a complete guide to how the command works, and what it does. Press “q” to exit man, space to page down, and enter to go one line at a time.
10.1.3
apropos <> If you cannot remember the command, apropos followed by a keyword will return all commands that have that keyword in the command on in its description.
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10.1.4
whatis <> Whatis is very similar to apropos. Before it can be used, run /usr/sbin/makewhatis
10.1.5
tab key The tab key will auto-complete either a command or a filename, pressing it twice in succession will return all options.
11 Filesystem Navigation and Commands There are a number of commands that are useful for navigating around the filesystem, and performing operations on the filesystem. There are usually a number of options with each command that change the output or behaviour of the command. Type <> -h for more information of the command or man <> to get a complete description.
11.1 # ls Like dir in Dos, it lists the current directory. It lists the contents of the current directory. With the –al switch, it displays the permissions and ownership of the files as well.
11.2 # cd Change Directory, type cd /path/to/directory cd / takes you to the root of the filesystem, while cd ~ takes you to your home directory. cd .. takes you up one directory level.
11.3 # pwd Tells you where you are in the directory system.
11.4 # cp copy, copies a file from one place to another, e.g cp file.txt ~ would copy the file.txt to your home directory. You can copy recursively, e.g the directory and all subdirectories using the –r switch
11.5 # mv Moves a file from one location to another. This is also a popular method of renaming a file. E.g. mv file.txt newfile.txt would rename file.txt to newfile.txt
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11.6 # mkdir mkdir <> make a new directory.
11.7 # find Find a file on the file system. This is memory intensive, so if the system is being used as a PBX, it may cause some voice quality issues. The usual syntax is find –name filename. Wildcards can be used such as * Note that the find command only looks in the current directory and all sub directories. So to search the complete file system, you need to either do cd / to get to the root of the file system,, or find / -name name* to find all files that begin with name.
11.8 # grep Searches the contents of the files for the word stated – e.g. grep -i tom would find all files with the word “tom” in them.
11.9 # rm Remove a file, Note that there is no undelete command, or recycle bin in Linux, so when a file is deleted, it is gone for ever. A tip to ensure that there are no mistakes is to try the command substituting ls for rm. E.g. to remove all files that end in txt you may want to type rm *.txt but try the command ls *.txt to ensure that it does what you think it is going to do. The –r switch deletes all subdirectories and their files. The –f forces the delete, and does not prompt, so if you have a large directory and subdirectory to delete, then a valid command would be rm –rf * which would delete everything in the current directory.
11.10 # touch Create an empty file. E.g. touch newfile.txt will create a new file called newfile.txt in the current directory.
11.11 Links / shortcuts The concept of shortcuts is available in Linux using the ln command. Make a link from a directory to a file or directory.
11.12 # wget Downloads a file from www.mysite.com/filename.txt
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12 Disk Usage
12.1 # du Shows the contents, directory and file sizes.
12.2 # df Shows the current disk usage. Note that if a hard drive becomes full. Linux will cease to work, and may become inaccessible to SSH. Where you are running an FTP site, it may be a good idea to put the FTP site on it’s own partition so that it’s becoming full does not cause problem with the operating system.
13 Editing and reading files
There are a large number of text editors available. We will cover Nano in this document, as it is easy for the beginner to use, with plenty of help. Note that files created in Windows applications such as Notepad or WordPad may not work on Linux systems because of the non standard way the Windows puts carriage returns and line breaks into files. Additionally, files that are moved via a Windows using the FTP ascii protocol may also be damaged because of this line feed issue. I would advise that all files are edited and moved within Linux. In most files, the “#” denotes that the following characters are simply comments. However, in Asterisk Dial plans, # means include the named file. Comments are denoted by a semi-colon “;” Other file types are commented differently // This is a PHP comment for a single phrase /* this comments out several lines in PHP code */
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13.1 Nano Nano is a GPL’d text editor for use at the Linux command line. To open or create a new file, type nano –w filename.txt The –w switch helps the system to read punctuation and make it more readable. When done editing type CTRL X Y Enter
13.2 WinSCP WinSCP can be used for editing files in a familiar Windows interface, simply right click on the file to edit, and click edit. Save when done.
13.3 # cat Cat lists the entire contents of a file in one go.
13.4 # less Lists the contents of a file one page at a time. Press q to exit. E.g. less myfile.txt
13.5 # tail Lists the last 10 lines of a file. There are switches to change this value. Tail –f logfilename shows the log in realtime.
13.6 # head Lists and displays the top 10 lines of a file.
14 File Ownership and permissions Every file is owned by one of the users on the system. Depending on the permissions assigned to that file depends on whether a file can be viewed, edited and executed.
14.1 The Basics Typing ls –al shows all the files and directories, with their ownership. There are 10 entries showing the permissions. For example: -rw-r--r-- 1 root root 23237 Feb 13 17:56 install.log
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drwxr-xr-x 2 root root
4096 Feb 14 00:08 centos-cd1
The first letter can be a:- = file - d = directory - l = link The next sections total 9 characters, and can be divided into three. -
1,2,3 = Owner permissions 4,5,6 = Group Permisions 7,8,9 = Others - Everyone else
Each section can have read, write and execute permissions. (r x and w)
14.2 Chmod (Parts reproduced from http://www.freeos.com/articles/3127/ By Mayank Sarup)
The command chmod modifies the permissions. It uses a system of numbers to apply the permissions. At its simplest, you can add execute permissions to a file simply by typing chmod +x somefile, which would add executable permissions to somefile. There is another way in which you can specify the file permissions. The permission bits r,w and x are assigned a number. -
r=4 w=2 x=1
Now you can use numbers, which are the sum of the various permission bits. E.g - rwx will be 4+3+1 = 7. rx becomes 4+1 = 5. The chmod command now becomes chmod xyz filename where x,y and z are numbers representing the permissions of user, group and others respectively. Each number is the sum of the permissions to be set and are calculated as given above. Chmod 644 somefile -
6 = 4 + 2 = rw 4=r 4=r
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As you can see, the permissions for somefile are being set to rwr--r--. This is a simpler and quicker way of setting the file permissions. Refer to the table below as a quick reference. -
0 - --1 - --x 2 - -w3 - -wx 4 - r— 5 - r-x 6 - rw7 – rwx
Tip: The easiest way to set the permissions is to right click on the file or directory in WinSCP, select properties. You can then tick the permission you want to allow.
14.3 Chown In addition to the file permission, you can also modify the owner and group of the file. The chown program is used here and its syntax is very simple. You need to be the owner of a file or root to do this. chown new-owner somefile Or to change the owner and the group recursively # chown –R Group:Owner /path/to/directory
14.4 chgrp To change group, user the chgrp command. Syntax is similar to chown. You will need to be the owner of the file and also belong to the same group as the file, or you should be root. chgrp new-grp somefile
15 Services Services on a Linux system are often known as Daemons. They typically run in the background and are launched at boot time.
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Typically, daemons end with a d as in sshd for the SSH service or Daemon. Services can be stopped, started, restarted and the status queried:Service <> status | start | stop |restart
15.1 # chkconfig To start services automatically at boot time, the chkconfig command is used. However, we need to know which run level is used. Normally this is three for our purposes. The run levels for CentOS are as follows: -
0 - Halt 1 - Single user 2 - Not used/User definable 3 - Full multi-user, console logins only 4 - Not used/User definable 5 - Full multi-user, with display manager as well as console logins 6 - Reboot
So if we want the SSH server to run in levels 3, 4 and 5 we would type: # chkconfig --level 345 sshd on to turn it off:# chkconfig --level 345 sshd off In order to discover what services are running type # chkconfig –list
15.2 /etc/rc.d/rc.local This file is like the windows startup folder. Processes and scripts can be launched from here at the end of the boot process.
15.3 Stopping services and processes. Usually an active session, such as a find, which is taking a long time can be stopped pressing CTRL C
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However sometimes, it is impossible to stop a service, so something more dramatic has to be used. This is the Linux equivalent of CTRL-ALT-DEL in Windows The first thing to discover is the process ID, or the PID.
15.4 # ps aux Shows a list of running processes, with the PID and some other metrics
15.5 # kill Kills the process. Kill 235 where 235 is the PID to kill
15.6 # kill -9 Force kills the process kill -9 235 force kills the PID
15.7 # top Shows the running processeswith the most processor intensive at the top. This displays in real-time.
16 Reboot and shutdown
16.1 # reboot Reboots the Server
16.2 # shutdown –h now Usage: message]
shutdown [-akrhHPfnc] [-t secs] time [warning -a: use /etc/shutdown.allow -k: don't really shutdown, only warn. -r: reboot after shutdown. -h: halt after shutdown. -P: halt action is to turn off power. -H: halt action is to just halt. -f: do a 'fast' reboot (skip fsck). -F: Force fsck on reboot. -n: do not go through "init" but go down real fast. -c: cancel a running shutdown. -t secs: delay between warning and kill signal. ** the "time" argument is mandatory! (try "now") **
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17 Pipe
17.1 # | The pipe command allows the output of one command to be piped into the input of another command.
17.2 Redirect Output The > symbol redirects output from a command to another destination such as a file so you can analyse the contents at your leisure. e.g. ls –al > list.txt willl send the output of ls –al to a the text file; list.txt
17.3 # > Appends to the end of an existing file.
17.4 ## >> Clears the file first. 18 Compression
In order to compress a file, or amalgamate a large number of files into one large file, the following commands can be used, or a directory or file can be compressed using the WinSCP utility. Strictly speaking, TAR, derived from tape archive is not really used for compression. The same extraction command will work. Note that unTAR’ing a TAR file extracts the files into the same directory tree in which they were stored beginning at the location from which the command is executed. Thus, if /var/myfile.txt is included in the archive, then extracting the archive from the root directory would place the file in /var while extracting the archive from /junk would place the file in /junk/var. There's another beauty and curse to tarballs. They preserve the ownership and permissions of the original files which are included in the archive. This includes the ownership and permissions of the original directory structure as well. If you are creating a tarball, be mindful of the consequences of creating a
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tarball with a directory structure with ownership and permissions which may differ from those on target systems. Creating a Tarball is a two stage process. First all the files are put into a TAR file, and then they are compressed using a compression utility such as Gzip or Bzip.
18.1 # tar Strictly speaking, TAR, derived from the words Tape ARchive is not really used for compression. It simply rolls a number of files into one big file (Tarball) The most popular command is tar –zxfv filename.tar.gz to extract the files from an existing archive. To archive and compress a file the following sequence is used: tar -cf filename.tar /etc/myfile.conf /var/lib/asterisk/agibin/somefile.php We can check that the tarfile is acceptable by executing tar -tf filename.tar Then we compress the tar file with: gzip filename.tar This returns a file called filename.tar.gz. .tar.gz and .tgz are used interchangeably Tip: For untarring a file, do it from the command line – tar zxfv filename.tar.gz. To tar and compress a file, it is easiest, and less prone to error if you do it from within WinSCP. Select the directories to be compressed, rightclick and select Tar.
18.2 # gzip As above
18.3 # bzip bzip –czvf filename.tar filename but using the bzip compression algorithm
18.4 # zip & unzip If a compressed file ends with the zip extension, use unzip to decompress.
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19 Networking In order to set up a machine on a network, you will need the following information. -
The IP address Netmask Gateway DNS server
Please note that the command netconfig has been deprecated, which is a fancy way of saying they’ve replaced it with something else.
19.1 # ifconfig Shows the current IP addresses of every interface, note that a physical interface can have more than one IP address.
19.2 # system-config-network A text based GUI to set the IP address of any interface. This utility writes to:/etc/sysconfig/network-scripts/ifcfg-eth0 in the case of network interface known as eth0. It can be manually edited if necessary. With a fixed IP address the file should look like this:DEVICE=eth0 ONBOOT=yes BOOTPROTO=static IPADDR=192.168.3.200 NETMASK=255.255.255.0 GATEWAY=192.168.3.254 Type service network restart to set the changes. Be careful you do not lock your self out with a typing error.
19.3 # resolv.conf The file containing the details of how to resolve an domain name to an IP address. To add a nameserver, type nano –w /etc/resolv.conf and add the line: Nameserver 1.2.3.4 Where 1.2.3.4 is the DNS server. Often, but not always, the gateway/router doubles up as the DNS Server
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Ping some internet domain names in order to check that DNS resolution is working.
19.4 # hostname Sets the name of the server.
19.5 # ifdown Stop the interface, e.g. ifdown eth0
19.6 # ifup Bring the interface back up again.
19.7 # ping Send a packet to a host and measure the time it takes to make the round trip. E.g. ping www.google.com
19.8 # traceroute Trace the route to a host. E.g. traceroute www.google.com
19.9 # mtr mtr is a very useful command combining ping and traceroute in the same command. It shows the live status of the path to a host. E.G. mtr www.google.com
20 Network Security There is no substitute for having a good firewall, but Linux contains IP tables that filter and manipulate packets. 20.1.1
Iptables IP tables are are found in /etc/sysconfig/iptables they can be managed by hand editing them, or it is much easier via Webmin. Open Webmin and navigate to Networking then Linux Firewall.
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21 Installing software There are a number of ways of getting software on the server, the following are methods are described below.
21.1 Compiling from source In many cases, programs can be compiled from source. That is to say that there is machine readable source code, and using development tools on the server, software can be compiled and installed. Generally, the software is untarred to /usr/src/<packagename>. Within the unzipped directory will be a readme file, or install.txt which should be read before proceeding to see if there is anything special that needs to be done. In general, the commands are as follows:21.1.1
# make clean Clean up any failed or previous installs. # ./configure
21.1.2
Checks and configures the package ready for compiling and installation, and ensures that all the dependencies are in place. If the there is hardware to be installed, there is a very good chance that you will need the kernel sources. (yum install kernel-devel) Watch the output for any errors. If there are dependencies missing, then these may have to be installed first, probably from the yum repositiory 21.1.3
# make Compile the program.
21.1.4
# make install Install the program
21.2 # yum Use the CentOS repository, and other repositories to install and update software. E.g.
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# Yum update updates the entire operating system. Note that if any hardware has been compiled against the kernel, ie.zaptel, then the package will have to recompiled as above. # yum search <package name> search for a package. # yum install <package name> # yum –y install <package name> ; installs programs without any further prompts.
21.3 # rpm Many programs, e.g. webmin come as an rpm, or a precompiled binary, so that the program does not have to be compiled on the machine. The usual command is rpm –iv <package name> If the package is available on the yum repository, it is usually better to install it from there. The RPM package may not be specific to your own Linux distribution.
22 Logs
There are a large number of logs on the system, which can give good information on any problems, who has accessed the machine, and what they have done with them. To view them, you can use less, tail, cat, and other similar commands as listed above. A few of the more important logs are below.
22.1 /var/log/messages Contains general system logging
22.2 /var/log/dmesg Contains hardware loading information
22.3 /var/log/asterisk/full Contains the Asterisk log file
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22.4 # logrotate Logs can get quite large, so it is important to do some housekeeping to ensure that the file system does not become full. This is usually done for you. But if not, read the man logrotate. 23 Crontab The crontab is a way of making timed events happen on a regular basis. They are also known as cron jobs. Cron jobs are easiest set up in Webmin. Crontabs can also be viewed and edited using crontab command at the command line. Once in crontab, the editing commands are the same as Vi editor, which is another text editor supplied with Linux, and is about as user friendly as a cornered rat. So I would urge you to use webmin for adding and editing. 24 Users and Groups
24.1 Users Users are people, and processes that have access to things on the system
24.2 Groups A group is a collection of users to make administration easier.
24.3 # sudo It is not necessarily desirable to have root as the main access to system. If hackers get access to the system, they can go everywhere. Additionally, it is possible to make a mistake on the system. By being a non root user, some of these mistakes can be mitigated. To set up a sudo user:# adduser myusername # passwd myusername <password>
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To edit the sudoers file to run sudfo commands, nano /etc/sudoers and add the following line: myusername ALL=(ALL) ALL Now simply execute commands as the root user by typing sudo… Alternatively, you can log on as root type “sudo –“ then enter the password. # sudo –i gives you complete root access without needing to prefix commands with sudo.
25 Network Services The server runs a few of the following services.
25.1 NTP A time server. Linux can get its time from the internet, and act as a time server for devices on your network. For this to happen, ntpd must be running (service ntpd status) and port 123 udp must be open on the firewall To force the computer to set the right time. # service ntpd stop # ntpdate 1.pool.ntp.org # service ntpd start Tip: Before commencing the installation of Linux, check that the hardware clock in BIOS is set to the right time and date, otherwise installation of packages may fail.
25.2 DNS Domain Name resolution. Linux can be a domain name server. The easiest way to set this up is in webmin. Click on servers, then Bind.DNS Server, and set it up with the default values offered by Webmin. Port 53 must be open to allow DNS queries
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25.3 DHCP DHCP, Dynamic Domain Name Server. Port 67 UDP must be open to deliver IP addresses to it clients. This can be set up and started in Webmin easily. If you wish to run a DHCP server on your machine, ensure that you start it as a service. Refer to chkconfig instructions above.
25.4 TFTP A TFTP server is what a phone and other devices use to get their configuration. Run these commands to get it running: # yum -y install tftp-server # /sbin/chkconfig --level 345 xinetd on # /sbin/chkconfig --level 345 tftp on # service xinetd restart To check it is running: netstat -nulp|grep 69
You should see a result that includes a line that looks similar to the following: udp 0 0 0.0.0.0:69 0.0.0.0:* 25.4.1
Option 66 Option 66 in the DHCP configuration is the setting that tells TFTP enabled devices where to find the TFTP server.
25.5 Sendmail / Postfix These programs are both popular programs for sending mail. To set them up the way you want them. Webmin is the best option for those with Conversational Linux
25.6 Apache The web server, that delivers web pages. The Daemon is called httpd. To restart apache, type httpd –k restart In general, the /var/www/html.
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25.7 PHP PHP is a language that when combined with Apache and MySQL allows interactivity with the web page. Adding, removing and displaying records from a database.
25.8 MySQL MySQL is one of the most popular database systems. It can handle many millions of records. If you have Apache and PHP installed, the database can be viewed via phpMyAdmin. See www.phpmyadmin.net. Do however note the licensing of MySQL. It is undergoing change due to a commercial buyout. 26 Hardware
26.1 # lspci Show the interrupts on the system, add –v for more information
26.2 # cat /proc/interrupts As above, but from a different source 27 SSH Tunnelling SSH has the ability to tunnel connections from your PC to any other IP address that the CentOS server has access to. This can be useful for reconfiguring routers or phones on the remote network. In putty, open a connection to the remote server. Once connected, click on the little icon in the top left hand corner of putty and select “Change Settings” In the left hand side bar, select Connection, SSH, Tunnels And you should end up with a screen like this: -
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27.1 Example One Assume that we want to connect to the router which is on 192.168.3.254 using port 80. Fill in the boxes as follows: •
Source port = 80
•
Destination port = 192.168.3.254:80
•
Leave Local and Auto as the defaults
Click add, then apply On your local browser, Firefox or Internet Explorer, type http://localhost and the router will appear in your web page.
27.2 Example Two You wish to connect to a number of phones on the network, that are on 192.168.3.201, 202, 203 etc, to match the extension numbers, 201, 202, 203 etc. You can add a number of tunnels, so to connect to 192.168.3.201 •
Source Port = 201
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•
Destination – 192.168.3.201:80
•
Click add, then add the next phone
•
Source Port = 202
•
Destination = 192.168.3.202:80
Click Add, and continue in this manner. When you have added all your phones, click Apply. •
To access extension 201, type http://localhost:201
•
To access extension 202, type http://localhost:202
Ports 201 and 202 were only chosen to make it easy to remember where to find the phones. Any source port can be chosen
28 Conclusion Now you have read this document, you should have enough information and tools to be able to do basic Linux installs, configuration and maintenance, as well as search for further information should you need to. The purpose of the above is not to give you a complete overview of Linux, but just enough to get you started, and carry out basic commands with an understanding of what you are doing in the context of installing a PBX.
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Copyright Jonathan Roper [email protected]
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1
About the Author Joe Roper Has had a commercial and operational background in the transport industry before moving into IT in the mid nineties, and into communications in the late nineties. Joe is one of the three lead developers with PBX in a Flash together with Ward Mundy and Tom King, both of whom have contributed to this document. Joe is also the Commercial Director or A2Billing. www.a2billing.net. A2Billing, licensed under the GPL, when combined with Asterisk is a physical Telecom Platform and Soft-Switch providing a wide range of telecoms services using either traditional telephone technology or VoIP. It contains a real-time billing engine which rates and bills and invoices calls, and contains a payment gateway. Joe is available for consultancy, Googling on "joe roper"+voip or "joe roper"+wireless will show some of the projects that Joe has been involved in, which may help establish his credentials. This document is offered in the hope that it may be useful, but no warranty for the accuracy of the document is either implied or given. Please pass on errors and suggestions for improvement on to [email protected] This document is released under the creative commons license – Attribution share. See http://creativecommons.org/licenses/by-sa/3.0/legalcode This license lets you remix, tweak, and build upon this work even for commercial reasons, as long as you credit Joe Roper and license your new creations under the identical terms. This license is often compared to open source software licenses. All new works based on yours will need to carry the same license, so any derivatives will also allow commercial use.
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2
Table of Contents
1
About the Author...........................................................................................................................................2
2
Table of Contents...........................................................................................................................................3
3
Introduction....................................................................................................................................................7
4
Open Source ...................................................................................................................................................7
5
4.1
What is Open Source ..............................................................................................................................8
4.2
Can I modify the software?.....................................................................................................................8
4.3
I want to make a Business and sell OSS based products. .....................................................................8
4.4
Can I Sell a Modified Version? ..............................................................................................................9
4.5
I’ve written a killer App for the product; do I need to give it away?....................................................9
4.6
So how do I make money? ....................................................................................................................10
Preparation...................................................................................................................................................10 5.1 Virtual Machine ....................................................................................................................................10 5.1.1 VMware........................................................................................................................................10 5.1.2 Microsoft Virtual PC....................................................................................................................11
6
5.2
Hardware ..............................................................................................................................................11
5.3
PuTTY....................................................................................................................................................12
5.4
WinSCP .................................................................................................................................................12
Installation of ISO .......................................................................................................................................13 6.1
Burning the ISO ....................................................................................................................................13
6.2
Installation preparation (Hardware)...................................................................................................14
6.3
Installation (vmware)............................................................................................................................14
7
Webmin.........................................................................................................................................................14
8
Linux for PBX systems ...............................................................................................................................15
9
8.1
Concept of Linux...................................................................................................................................15
8.2
Why CentOS ..........................................................................................................................................15
8.3
The Command Line...............................................................................................................................16
8.4
GUI – startx...........................................................................................................................................16
8.5
Accessing the System ............................................................................................................................17
8.6
SSH and Putty .......................................................................................................................................17
8.7
SSH and WinSCP..................................................................................................................................18
8.8
SSH ........................................................................................................................................................20
8.9
SCP ........................................................................................................................................................20
Linux Filesystem..........................................................................................................................................20 9.1
Linux File System Explained ................................................................................................................21
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9.2 Directories.............................................................................................................................................22 9.2.1 /sbin...............................................................................................................................................22 9.2.2 /bin ................................................................................................................................................22 9.2.3 /boot ..............................................................................................................................................22 9.2.4 /dev................................................................................................................................................22 9.2.5 /etc.................................................................................................................................................23 9.2.6 /home ............................................................................................................................................23 9.2.7 /lib .................................................................................................................................................23 9.2.8 /lost+found....................................................................................................................................23 9.2.9 /mnt ...............................................................................................................................................24 9.2.10 /opt ................................................................................................................................................24 9.2.11 /proc ..............................................................................................................................................24 9.2.12 /root...............................................................................................................................................24 9.2.13 /tmp ...............................................................................................................................................24 9.2.14 /usr.................................................................................................................................................24 9.2.15 /var ................................................................................................................................................25 10
Command Line Construction................................................................................................................25 10.1 Where to get help ..................................................................................................................................25 10.1.1 --help or --h...................................................................................................................................25 10.1.2 man <
11
Filesystem Navigation and Commands................................................................................................26 11.1
# ls..........................................................................................................................................................26
11.2
# cd.........................................................................................................................................................26
11.3
# pwd .....................................................................................................................................................26
11.4
# cp.........................................................................................................................................................26
11.5
# mv........................................................................................................................................................26
11.6
# mkdir...................................................................................................................................................27
11.7
# find......................................................................................................................................................27
11.8
# grep.....................................................................................................................................................27
11.9
# rm........................................................................................................................................................27
11.10
# touch...............................................................................................................................................27
11.11
Links / shortcuts................................................................................................................................27
11.12
# wget ................................................................................................................................................27
12
Disk Usage ................................................................................................................................................28 12.1
# du ........................................................................................................................................................28
12.2
# df .........................................................................................................................................................28
13
Editing and reading files ........................................................................................................................28 13.1
Nano ......................................................................................................................................................29
13.2
WinSCP .................................................................................................................................................29
13.3
# cat .......................................................................................................................................................29
13.4
# less ......................................................................................................................................................29
13.5
# tail.......................................................................................................................................................29
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13.6 14
# head ....................................................................................................................................................29 File Ownership and permissions...........................................................................................................29
14.1
The Basics .............................................................................................................................................29
14.2
Chmod ...................................................................................................................................................30
14.3
Chown....................................................................................................................................................31
14.4
chgrp......................................................................................................................................................31
15
Services .....................................................................................................................................................31 15.1
# chkconfig ............................................................................................................................................32
15.2
/etc/rc.d/rc.local ....................................................................................................................................32
15.3
Stopping services and processes. .........................................................................................................32
15.4
# ps aux..................................................................................................................................................33
15.5
# kill .......................................................................................................................................................33
15.6
# kill -9...................................................................................................................................................33
15.7
# top .......................................................................................................................................................33
16
Reboot and shutdown.............................................................................................................................33 16.1
# reboot..................................................................................................................................................33
16.2
# shutdown –h now ...............................................................................................................................33
17
Pipe............................................................................................................................................................34 17.1
# | ...........................................................................................................................................................34
17.2
Redirect Output.....................................................................................................................................34
17.3
# >..........................................................................................................................................................34
17.4
## >>.....................................................................................................................................................34
18
Compression ............................................................................................................................................34 18.1
# tar........................................................................................................................................................35
18.2
# gzip......................................................................................................................................................35
18.3
# bzip......................................................................................................................................................35
18.4
# zip & unzip .........................................................................................................................................35
19
Networking...............................................................................................................................................36 19.1
# ifconfig................................................................................................................................................36
19.2
# system-config-network.......................................................................................................................36
19.3
# resolv.conf ..........................................................................................................................................36
19.4
# hostname.............................................................................................................................................37
19.5
# ifdown .................................................................................................................................................37
19.6
# ifup......................................................................................................................................................37
19.7
# ping .....................................................................................................................................................37
19.8
# traceroute ...........................................................................................................................................37
19.9
# mtr.......................................................................................................................................................37
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20
Network Security.....................................................................................................................................37 20.1.1
21
Iptables..........................................................................................................................................37
Installing software...................................................................................................................................38 21.1 Compiling from source .........................................................................................................................38 21.1.1 # make clean.................................................................................................................................38 21.1.2 # ./configure..................................................................................................................................38 21.1.3 # make...........................................................................................................................................38 21.1.4 # make install................................................................................................................................38 21.2
# yum .....................................................................................................................................................38
21.3
# rpm......................................................................................................................................................39
22
Logs ...........................................................................................................................................................39 22.1
/var/log/messages..................................................................................................................................39
22.2
/var/log/dmesg.......................................................................................................................................39
22.3
/var/log/asterisk/full ..............................................................................................................................39
22.4
# logrotate .............................................................................................................................................40
23
Crontab.....................................................................................................................................................40
24
Users and Groups....................................................................................................................................40 24.1
Users......................................................................................................................................................40
24.2
Groups...................................................................................................................................................40
24.3
# sudo.....................................................................................................................................................40
25
Network Services.....................................................................................................................................41 25.1
NTP........................................................................................................................................................41
25.2
DNS........................................................................................................................................................41
25.3
DHCP ....................................................................................................................................................42
25.4 TFTP......................................................................................................................................................42 25.4.1 Option 66......................................................................................................................................42 25.5
Sendmail / Postfix..................................................................................................................................42
25.6
Apache...................................................................................................................................................42
25.7
PHP .......................................................................................................................................................43
25.8
MySQL...................................................................................................................................................43
26
Hardware..................................................................................................................................................43 26.1
# lspci....................................................................................................................................................43
26.2
# cat /proc/interrupts ............................................................................................................................43
27
28
SSH Tunnelling........................................................................................................................................43 27.1
Example One.........................................................................................................................................44
27.2
Example Two.........................................................................................................................................44 Conclusion................................................................................................................................................45
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3
Introduction The purpose of the manual is to explain some basic commands for Linux to the Windows user, to give them confidence to use Linux. Linux, in the PBX environment does not usually have a graphical user interface. However even if it did, it would be more complicated to explain that then to simply use the command line interface. Linux differs from Windows in that a range of windows Managers and graphical user interfaces can be used, the most popular of which are Gnome and KDE. The following sections should give some techniques that the user, more familiar with Windows, can use to manage and configure their PBX system. This manual concentrates on the CentOS (Community Enterprise Operating System) as this is one of the most widely used in PBX deployments. It is based on Red Hat Enterprise Linux (RHEL) and is supported for seven years after release. By the time you have practiced the commands in this manual, you should have “Conversational Linux”
4
Open Source There has been an explosion and growth of open source software in the last few years, especially in the telecoms market. Open Source software in many cases is every bit as good as the commercial equivalent. The first thing to understand is that Open Source Licensing is in no way anti-commercial. OSS software is, and always has been commercial. What it is, is Anti Lock in. For your customers, OSS is a huge selling point. They will always be able to get support for their product, even if they do not buy it from you. If you do a good job, then of course they will have no reason to move.
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4.1 What is Open Source Open Source software is software that is released under a license that allows you to modify the program to suit yourself. Open Source is generally but not always free of charge. Open Source software used to be called Free Software. The Free in the name DID NOT refer to the price, but to the Freedom to modify and alter the program. One of the most popular licenses is GPL v2 – http://www.gnu.org/licenses/old-licenses/gpl-2.0.html. There is a GPL v3, but this has not been widely adopted as yet. The idea with OSS software is that you can contribute to the development of the product, and enjoy the fruits of your labour. The code can be inspected by your peers, and commented about publicly. This concentrates the mind to do it properly. A worthwhile read is the Beekeeper analogy http://wiki.pentaho.org/display/BEEKEEPER/The+Beekeeper The advice below is based opinion, and before making commercial decisions based on this advice, you would be advised to do your own research.
4.2 Can I modify the software? If the software is for your own use, you can do whatever you want with it. There are no restrictions of any note. However, if you are going to re-distribute or sell your software, read on. It is a good idea to return your modifications back to the community for inclusion in future releases. In this way, when a new feature is added, you may not have to re-apply your modifications, and the product gets ever better. Remember that the copyright is still held by the original developer, so if you take a script, copy it, and pass it off as your own, and place your own copyright on it, that is illegal, and morally wrong.
4.3 I want to make a Business and sell OSS based products. You may redistribute GPL software, and indeed you may make a charge for the software. You must give the same rights to your customers as you have received from the original distributor of the OSS software. So given that you have the right to modify the
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software, so does your customer. They also have the right to redistribute the software as well. You can make more money by adding other elements to the sale, such as hardware, guarantees, training, and support
4.4 Can I Sell a Modified Version? Yes, you can make modifications to the software. However, any changes that you make to the software must be clearly marked and commented. If you make a mistake and break something, the reputations of the original developers should not be affected.(Section 2a of the GPL) Additionally, under the terms of the GPL, you must make your modifications freely (as in make no charge) available to any and all third parties, e.g. post a link to it on your website. (Section 2b of the GPL) So you can re-brand as your own? The basic tenant of Copyright law is that it gives the copyright holder the right to be credited for the work. In order to be sure, you would need to take legal advice, or simply ask permission of the copyright holder. The copyright law is nothing to do with the GPL. However, it is good manners, and a good strategy to talk to the original developers to get them to provide or give permissions fort a re-branded system, for which they make a charge which goes to support the project, and of course, updates and changes to the original code are unlikely to break your customised copy, and of course you stay in the development loop.
4.5 I’ve written a killer App for the product; do I need to give it away? You may write an application or modification to the product, but do not want to release the code as it gives you a competitive advantage. The answer to this is a little more grey, and to a great degree, depends on your moral radar’ A suggested guideline is that if you have to modify the original released code in order to make your application work, then your work will have to fall under the GPL. If you do not release the code to the GPL, then you could be in breach of the license, and lose the right to use the product. (Section 4 of the GPL) If the code communicates at arms length from the original code, then that is acceptable. (Read Section 2c carefully)
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4.6 So how do I make money? Providers of OSS software want you to make money from their work. That’s the point. Of course they would also like money and receive help as well. There are a number of ways that both the provider of the OSS software and the reseller can make money from OSS. 1. If the code is an original work, licensed under the GPL, then the developers and project owners may make a charge for the software. The purchaser of the software can resell the software if they wish, or indeed give it away if they so desire. After all, they still own the copyright. 2. Sell installation services, support and guarantees with the product, See Digium as an example of this. 3. Provide other Value Add Services, e.g. minutes and DID for PBX services. 4. Provide and sell documentation for the project. 5. Provide a service for updating and fixing the product. 5
Preparation To work through the exercises below, a test machine is required, virtual or real, as well as some useful tools to be downloaded from the internet. An internet connection is also required.
5.1 Virtual Machine A virtual machine is a program that allows operating systems to run in a window on a Windows, Linux or Mac PC. For the purposes of this manual, we will be concentrating on Windows. Note that it is not generally possible to run a production PBX on a virtual PC or server. Installing a virtual machine on a PC will not affect any existing data on the server. 5.1.1 VMware VMware from, www.vmware.com is one of the most popular virtual environments, as it supports all the major operating systems.
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In our case we only need VMware player, which will play an existing VMware image. VMware player is free of charge, but you do have to register to download it. You will need a VMware hard disk, and the .vmx configuration file. The .vmx file controls the attributes of the virtual machine, such as the memory, presence of network interfaces, the CDRom etc. It is a text file can be edited with notepad or wordpad. There is a blank hard disk and basic configuration file available from: http://www.pbxinaflash.com/downloads/pbxinaflash.zip
Alternatively, you can upgrade to VMware server, which has a cost, to create your own VMware disks. There is also a free open source program called VMX Builder, which will allow you to create your own hard disks and machine configurations. This can be found at: http://petruska.stardock.net/software/VMware.html 5.1.2 Microsoft Virtual PC There is another virtual machine program available to you called Virtual PC, which is a free download from Microsoft. This is available from:http://www.microsoft.com/windows/products/winfamily/virtu alpc/default.mspx For server grade hardware, Microsoft Virtual Server is also available. During the installation of Microsoft Virtual PC, there may be warnings about the operating system not being compatible. This is the case with Windows XP home edition. Note the warnings and continue with the install. There seem to be no side effects to installing VPC with Windows XP, despite the warnings.
5.2 Hardware Almost any hardware will do to run Linux on. Bear in mind that most Linux installs will delete any data on the PC, so do not install your main machine.
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Hardware that should be excluded with CentOS 5, the OS we will be using for this manual, is anything with an i586 architecture, as this is not supported. An example of this hardware would be a Via EPIA C3 processor. 10Gb is more than sufficient for the hard drive. 256Mb of RAM or more is recommended. Motherboards with onboard LAN may or may not be supported. It has been noted that Nvidia chipsets do have problems recognising the LAN, so it may be necessary to buy a network card to circumvent this problem. It will only be a matter of time before CentOS provides the drivers for more modern hardware. The advice is to research the motherboard on the internet to see if there are likely to be any compatibility problems.
5.3 PuTTY PuTTY is a windows program used to remote manage Linux machines from the command line. It gives a window onto the Linux machine, and any commands typed into the Putty window are executed on the remote machine. Putty is available from http://www.chiark.greenend.org.uk/~sgtatham/putty/ It is one executable file, so it can be run from a Windows desktop without needing to install it on the machine. It can be simply deleted afterwards if you are on a guest on some else’s machine. Putty is free of charge
5.4 WinSCP WinSCP is a program similar to Windows Explorer. It is a good program for those more used to Windows than they are to the command line. It allows drag and drop copying to and from the desktop, as well as changing permissions on files, editing files, and running non interactive commands. WinSCP is available from http://winscp.net/eng/index.php
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Note that this program is installed into Windows, so it may not be suitable for installing on a guest PC. WinSCP is free of charge 6
Installation of ISO One can download the ISO’s prepared by the various PBX aggregators such as PBX in a Flash, or CentOS can be downloaded from the CentOS website. There are ISO images on DVD and CD for many different computer architectures. The one we will most likely to be interested in is the i386 architecture. However, modern hardware and processors often support 64bit operating systems, so you may also wish to try the x86_64 download as well, which will make full use of the architecture and 64 bit capabilities. 64 bit machines can address far more memory. Typically, 32 bit architecture can only address up to 4Gb of memory, whereas 64 bit can address considerably more. Any more than 4Gb of memory on a 32 bit operating system is a waste of money, unless a special kernel is compiled.
6.1 Burning the ISO When the ISO has been downloaded e.g. pbxinaflash.iso it needs to be burnt to a CD. An ISO image is an image of the disk, which tells the CD burner where to put the relevant files and directories. It is not sufficient to simply copy the ISO onto the CD, it needs to be burnt properly. The usual, most popular tool to do this is Nero. This program is often bundled with PC’s from OEM distributors. Depending on the version, look for “Burn CD image” If Nero is not available, then there is a Windows power toy available from http://isorecorder.alexfeinman.com/isorecorder.htm which will burn an ISO image onto CD.
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Note that on virtual machines, it is not necessary to burn the ISO to a physical CD, as the VM image allows you to mount the ISO image as if it was a physical CD.
6.2 Installation preparation (Hardware) The first job is to make the machine bootable from the CDROM drive. Hardware varies, but in most cases it is necessary to enter the BIOS, often by pressing F2, or del during the initial boot up. Once the BIOS is open, then the boot order can be altered so it boots from CD first, and then the hard drive. In other cases, it may be necessary to press a key combination to enter the boot options, e.g. F12. This allows you to select the boot device. Chose CDROM. For machines without a CDROM, a USB CDROM drive may have to be purchased, and a modern PC should boot from a USB interface. This may not be the case with older machines. Ensure that all data that you want to keep has been backed up. To check that the CD is in good order, then at the boot of the CD, type linux mediacheck.
6.3 Installation (vmware) On a fresh virtual machine, there will be no requirement to do any preparation apart from to ensure that the ISO image is in the right place relative to the VM image. For VMware, open the .vmx file and find the line which points to the ISO e.g. ide0:1.fileName = "c:\ippbx\concordiax.iso" Ensure it points to the filename of the ISO image. In Microsoft VPC, simply check the properties and options. Future installations over the top of existing installs will require you to bring up the boot order menu. In VMware, press escape as the system boots. Be quick or you will miss it. 7
Webmin Webmin is the swiss army knife of Linux administration for the Linux Conversational. It simplifies changes to be made to the system. It allows the configuration of Linux though a web based UI, which runs separately in its own process.
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Webmin is a web based application. By default, it is installed on port 10,000 however that port is sometimes changed for security. E.g. PiaF puts Webmin on 9001. To access Webmin, type the URL of your server appended with “:10000” e.g. http://myserver.com:10000 or in some cases https://myserver.com:10000 If Webmin is installed after the operating system, the password is usually the same as the root password. However, if it is installed with the OS, then the password has to be set separately. 8
Linux for PBX systems
8.1 Concept of Linux Linux is based on Unix which is a very mature operating system. Linux is known to be very robust, and suits “always on” applications as it can be run for many years without needing a reboot. The stability is maintained by the mindset of most Linux developers. Most Linux programs only do one thing, but do it really well. The make up of most operating systems is based on a layered model, and programs and functions only talk to their direct neighbours. E.G. -
Hardware talks to the Kernel The Kernel talks to applications.
In this way the kernel knows all about the hardware in a machine, and does not allow applications to talk directly to the hardware, which may cause a conflict. Thus, whenever new hardware is added, it may be necessary to recompile the kernel, or compile the hardware drivers against the kernel so that they know how to interact with each other.
8.2 Why CentOS A quick Google will throw up a lot of Linux distributions which have their own positives and negatives. People are as loyal to their particular distribution as they are to their football team.
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There are advantages and disadvantages to them all, but, a choice as to be made, in this case, CentOS has been chosen. CentOS is Redhat Linux with all the branding taken out. RHEL is not usually available free of charge, and requires an annual support fee, and as such, has lots of paid developers working on the system. Not surprisingly, this allows it to spend more money on the development and support of hardware, and has been adopted as the defacto distribution for servers. Fedora Core is the hairy bleeding edge of RHEL. Older versions of Fedora Core cascade into RHEL, which in turn is released as CentOS. CentOS is distributed completely free of charge, and is licensed under the GPL. The reasons for choosing Centos, is that enjoys the same benefits of RHEL. RHEL updates are usually ported into CentOS within 72 hours of them becoming available. CentOS is maintained for seven years after release, so the current 5.1 release is set to be supported until 2014. A side benefit is that if you were to ever release a PBX where the customer wanted to have some guarantees about the stability, a PBX could easily be built using RHEL and Asterisk Business Edition. For more information on Centos, see www.centos.org
8.3 The Command Line With a PBX install, it is not usually necessary to spend too long at the command line. Only long enough to configure the hardware, software and network and do any trouble shooting that may be required. After this time, most configurations are done via web pages.
8.4 GUI – startx Graphical user interfaces (also known as X) can be installed to CentOS, and there are a few choices. However, GUI’s are rarely installed on Servers, as servers are rarely touched once installed. GUI’s use quite a lot OS system resources. If no one is looking at the GUI, then there is no point in one being present.
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Having said that, the amount of resources required to run a GUI on a modern server is only a small percentage of the available power. If a GUI has been installed, then it can be started with the command startx. When you have finished with the GUI, it can be stopped with the key combination CTRL-ALT-BACKSPACE.
8.5 Accessing the System The main method of accessing the server is via a protocol called SSH. Secure Shell. The commands and screen output is encrypted, so it is a secure method of connecting. SSH is a TCP connection on port 22. For a public server, this may need to be changed to a non standard port.
8.6 SSH and Putty To access the command line from Windows, PuTTY has to be launched. It will bring up a screen as below:-
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Simply fill in the IP address or hostname and click open.
You will then be prompted for the username - usually root, press enter, then type the password. As you are typing the password, there will be no screen output, so just keep typing and press enter. If authenticated properly, then you will end up in your home directory. In the case of root, you will be in the /root directory When first connecting to a Linux machine, you will get a prompt if you have never connected before. Accept this prompt. If you have connected to the machine before and you get this prompt, and then ensure that you have not been redirected to another machine. To copy a command from the Windows desktop, right click and copy the text, click in the Putty window and right click. This will paste the contents of the clipboard into the remote machine at the command prompt. To copy from the Putty window, simply highlight the text to be copied. This places the text on the windows clipboard. Right click to paste the text at the command prompt, or paste the contents into another Windows application
8.7 SSH and WinSCP WinSCP is a program which gives you a window onto the remote machine.
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WinSCP also comes with its own internal text editor.
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8.8 SSH It is possible to ssh from one Linux machine to another. Simply type ssh ipaddress or ssh root@ipaddress.
8.9 SCP Secure copy. Copy a file. Using the SCP protocol, copy files from one Linux machine to another.
9
Linux Filesystem The Linux file system has a number of partitions. At its most simple, it contains three partitions: -
-
The boot partition – this contains the mechanism to boot the system. The Swap partition – This is where stuff held in RAM is shifted to the hard drive, which pretends to be RAM, albeit, very much slower. The main file system – this contains the files and folders as well as applications.
There is no need to worry about this too much. For the moment, just go with the options offered to your doing the install.
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9.1 Linux File System Explained Original article by Mayank Sarup [email protected] Posted: (2001-01-03 10:08:44 EST http://www.freeos.com/articles/3102 )
The first thing that most new users shifting from Windows will find confusing is navigating the Linux file system. The Linux file system does things a lot more differently than the Windows file system. This article explains the differences and takes you through the layout of the Linux file system. For starters, there is only a single hierarchal directory structure. Everything starts from the root directory, represented by '/', and then expands into sub-directories. Where DOS/Windows had various partitions and then directories under those partitions, Linux places all the partitions under the root directory by 'mounting' them under specific directories. Closest to root under Windows would be c:. Under Windows, the various partitions are detected at boot and assigned a drive letter. Under Linux, unless you mount a partition or a device, the system does not know of the existence of that partition or device. This might not seem to be the easiest way to provide access to your partitions or devices but it offers great flexibility. This kind of layout, known as the unified file system, does offer several advantages over the approach that Windows uses. Let's take the example of the /usr directory. This directory off the root directory contains most of the system executables. With the Linux file system, you can choose to mount it off another partition or even off another machine over the network. The underlying system will not know the difference because /usr appears to be a local directory that is part of the local directory structure! How many times have you wished to move around executables and data under Windows, only to run into registry and system errors? Try moving c:/windows/system to another partition or drive. (No; Don't!!!) Another point likely to confuse new users is the use of the frontslash '/' instead of the backslash '' as in DOS/Windows. So c:\windows\system would be /c/windows/system. Well, Linux is not going against convention here. Unix has been around a lot longer than Windows and was the standard a lot before Windows was. Rather, DOS took the different path, using '/' for command-line options and “\” as the directory separator.
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To liven up matters even more, Linux also chooses to be case sensitive. What this means that the case, whether in capitals or not, of the characters becomes very important. So this is not the same as THIS or ThIs for that matter. This one feature probably causes the most problems for new users.
9.2 Directories We now move on to the layout or the directory structure of the Linux file system. Given below is the result of a 'ls -p' in the root directory. bin/ dev/ home/ lost+found/ proc/ sbin/ usr/ boot/ etc/ lib/ mnt/ root/ tmp/ var/ 9.2.1 /sbin This directory contains all the binaries that are essential to the working of the system. These include system administration as well as maintenance and hardware configuration programs. Find lilo, fdisk, init, ifconfig etc here. These are the essential programs that are required by all the users. Another directory that contains system binaries is /usr/sbin. This directory contains other binaries of use to the system administrator. This is where you will find the network daemons for your system along with other binaries that only the system administrator has access to, but which are not required for system maintenance, repair etc. 9.2.2 /bin In contrast to /sbin, the bin directory contains several useful commands that are used by both the system administrator as well as non-privileged users. This directory usually contains the shells like bash, csh etc. as well as much used commands like cp, mv, rm, cat, ls. There also is /usr/bin, which contains other user binaries. These binaries on the other hand are not essential for the user. The binaries in /bin however, a user cannot do without. 9.2.3 /boot This directory contains the system map file as well as the Linux kernel. Lilo places the boot sector backups in this directory. 9.2.4 /dev This is a very interesting directory that highlights one important characteristic of the Linux file system - everything is a file or a
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directory. Look through this directory and you should see hda1, hda2 etc, which represent the various partitions on the first master drive of the system. /dev/cdrom and /dev/fd0 represent your CDROM drive and your floppy drive. This may seem strange but it will make sense if you compare the characteristics of files to that of your hardware. Both can be read from and written to. Take /dev/dsp, for instance. This file represents your speaker device. So any data written to this file will be re-directed to your speaker. Try 'cat /etc/lilo.conf > /dev/dsp' and you should hear some sound on the speaker. That's the sound of your lilo.conf file! Similarly, sending data to and reading from /dev/ttyS0 ( COM 1 ) will allow you to communicate with a device attached there - your modem. 9.2.5 /etc This directory contains all the configuration files for your system. Your lilo.conf file lies in this directory as does hosts, resolv.conf and fstab. Under this directory will be X11 subdirectory which contains the configuration files for X. More importantly, the /etc/rc.d directory contains the system startup scripts. This is a good directory to backup often. It will definitely save you a lot of re-configuration later if you re-install or lose your current installation. 9.2.6 /home Linux is a multi-user environment so each user is also assigned a specific directory which is accessible only to them and the system administrator. These are the user home directories, which can be found under /home/username. This directory also contains the user specific settings for programs like IRC, X etc. 9.2.7 /lib This contains all the shared libraries that are required by system programs. Windows equivalent to a shared library would be a DLL file. 9.2.8 /lost+found Linux should always go through a proper shutdown. Sometimes your system might crash or a power failure might take the machine down. Either way, at the next boot, a lengthy file system check using fsck will be done. Fsck will go through the system and try to recover any corrupt files that it finds. The result of this recovery operation will be placed in this directory. The files recovered are not likely to be complete or make much
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sense but there always is a chance that something worthwhile is recovered. 9.2.9 /mnt This is a generic mount point under which you mount your file systems or devices. Mounting is the process by which you make a file system available to the system. After mounting your files will be accessible under the mount-point. This directory usually contains mount points or sub-directories where you mount your floppy and your CD. You can also create additional mountpoints here if you want. There is no limitation to creating a mount-point anywhere on your system but convention says that you do not litter your file system with mount-points. 9.2.10
/opt This directory contains all the software and add-on packages that are not part of the default installation. Generally you will find KDE and StarOffice here. Again, this directory is not used very often as it's mostly a standard in Unix installations.
9.2.11
/proc This is a special directory on your system that is a pseudo file system held in memory and tracks running processes on the machine. Most of the information is /proc is updated live to match the current state of the operating system.
9.2.12
/root We talked about user home directories earlier and well this one is the home directory of the user root. This is not to be confused with the system root, which is directory at the highest level in the file system.
9.2.13
/tmp This directory contains mostly files that are required temporarily. Many programs use this to create lock files and for temporary storage of data. On some systems, this directory is cleared out at boot or at shutdown.
9.2.14
/usr This is one of the most important directories in the system as it contains all the user binaries. X and its supporting libraries can be found here. User programs like telnet, ftp etc are also placed here. /usr/doc contains useful system documentation.
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/usr/src/linux contains the source code for the Linux kernel. If you are compiling programs from source such as Asterisk, you would put the source files under /usr/src 9.2.15
/var This directory contains spooling data like mail and also the output from the printer daemon. The system logs are also kept here in /var/log/messages. You will also find the database for BIND in /var/named and for NIS in /var/yp. This was a short and basic look at the Linux file system. You do need to have at least this basic knowledge of the layout of the file system to fully utilize its potential. One good place to read about the file system is this detailed document at www.pathname.com/fhs/1.2/fsstnd-toc.html that specifies the standard structure of the Linux file system.
10 Command Line Construction Most Linux commands are formed in the same way: Command – options Filename Below is a list of resources on the server to get information on a particular command.
10.1 Where to get help 10.1.1
--help or --h Typing a command followed with –help will generally give a quick aide memoire on the command
10.1.2
man <
10.1.3
apropos <
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10.1.4
whatis <
10.1.5
tab key The tab key will auto-complete either a command or a filename, pressing it twice in succession will return all options.
11 Filesystem Navigation and Commands There are a number of commands that are useful for navigating around the filesystem, and performing operations on the filesystem. There are usually a number of options with each command that change the output or behaviour of the command. Type <
11.1 # ls Like dir in Dos, it lists the current directory. It lists the contents of the current directory. With the –al switch, it displays the permissions and ownership of the files as well.
11.2 # cd Change Directory, type cd /path/to/directory cd / takes you to the root of the filesystem, while cd ~ takes you to your home directory. cd .. takes you up one directory level.
11.3 # pwd Tells you where you are in the directory system.
11.4 # cp copy, copies a file from one place to another, e.g cp file.txt ~ would copy the file.txt to your home directory. You can copy recursively, e.g the directory and all subdirectories using the –r switch
11.5 # mv Moves a file from one location to another. This is also a popular method of renaming a file. E.g. mv file.txt newfile.txt would rename file.txt to newfile.txt
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11.6 # mkdir mkdir <
11.7 # find Find a file on the file system. This is memory intensive, so if the system is being used as a PBX, it may cause some voice quality issues. The usual syntax is find –name filename. Wildcards can be used such as * Note that the find command only looks in the current directory and all sub directories. So to search the complete file system, you need to either do cd / to get to the root of the file system,, or find / -name name* to find all files that begin with name.
11.8 # grep Searches the contents of the files for the word stated – e.g. grep -i tom would find all files with the word “tom” in them.
11.9 # rm Remove a file, Note that there is no undelete command, or recycle bin in Linux, so when a file is deleted, it is gone for ever. A tip to ensure that there are no mistakes is to try the command substituting ls for rm. E.g. to remove all files that end in txt you may want to type rm *.txt but try the command ls *.txt to ensure that it does what you think it is going to do. The –r switch deletes all subdirectories and their files. The –f forces the delete, and does not prompt, so if you have a large directory and subdirectory to delete, then a valid command would be rm –rf * which would delete everything in the current directory.
11.10 # touch Create an empty file. E.g. touch newfile.txt will create a new file called newfile.txt in the current directory.
11.11 Links / shortcuts The concept of shortcuts is available in Linux using the ln command. Make a link from a directory to a file or directory.
11.12 # wget Downloads a file from www.mysite.com/filename.txt
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12 Disk Usage
12.1 # du Shows the contents, directory and file sizes.
12.2 # df Shows the current disk usage. Note that if a hard drive becomes full. Linux will cease to work, and may become inaccessible to SSH. Where you are running an FTP site, it may be a good idea to put the FTP site on it’s own partition so that it’s becoming full does not cause problem with the operating system.
13 Editing and reading files
There are a large number of text editors available. We will cover Nano in this document, as it is easy for the beginner to use, with plenty of help. Note that files created in Windows applications such as Notepad or WordPad may not work on Linux systems because of the non standard way the Windows puts carriage returns and line breaks into files. Additionally, files that are moved via a Windows using the FTP ascii protocol may also be damaged because of this line feed issue. I would advise that all files are edited and moved within Linux. In most files, the “#” denotes that the following characters are simply comments. However, in Asterisk Dial plans, # means include the named file. Comments are denoted by a semi-colon “;” Other file types are commented differently // This is a PHP comment for a single phrase /* this comments out several lines in PHP code */
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13.1 Nano Nano is a GPL’d text editor for use at the Linux command line. To open or create a new file, type nano –w filename.txt The –w switch helps the system to read punctuation and make it more readable. When done editing type CTRL X Y Enter
13.2 WinSCP WinSCP can be used for editing files in a familiar Windows interface, simply right click on the file to edit, and click edit. Save when done.
13.3 # cat Cat lists the entire contents of a file in one go.
13.4 # less Lists the contents of a file one page at a time. Press q to exit. E.g. less myfile.txt
13.5 # tail Lists the last 10 lines of a file. There are switches to change this value. Tail –f logfilename shows the log in realtime.
13.6 # head Lists and displays the top 10 lines of a file.
14 File Ownership and permissions Every file is owned by one of the users on the system. Depending on the permissions assigned to that file depends on whether a file can be viewed, edited and executed.
14.1 The Basics Typing ls –al shows all the files and directories, with their ownership. There are 10 entries showing the permissions. For example: -rw-r--r-- 1 root root 23237 Feb 13 17:56 install.log
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drwxr-xr-x 2 root root
4096 Feb 14 00:08 centos-cd1
The first letter can be a:- = file - d = directory - l = link The next sections total 9 characters, and can be divided into three. -
1,2,3 = Owner permissions 4,5,6 = Group Permisions 7,8,9 = Others - Everyone else
Each section can have read, write and execute permissions. (r x and w)
14.2 Chmod (Parts reproduced from http://www.freeos.com/articles/3127/ By Mayank Sarup)
The command chmod modifies the permissions. It uses a system of numbers to apply the permissions. At its simplest, you can add execute permissions to a file simply by typing chmod +x somefile, which would add executable permissions to somefile. There is another way in which you can specify the file permissions. The permission bits r,w and x are assigned a number. -
r=4 w=2 x=1
Now you can use numbers, which are the sum of the various permission bits. E.g - rwx will be 4+3+1 = 7. rx becomes 4+1 = 5. The chmod command now becomes chmod xyz filename where x,y and z are numbers representing the permissions of user, group and others respectively. Each number is the sum of the permissions to be set and are calculated as given above. Chmod 644 somefile -
6 = 4 + 2 = rw 4=r 4=r
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As you can see, the permissions for somefile are being set to rwr--r--. This is a simpler and quicker way of setting the file permissions. Refer to the table below as a quick reference. -
0 - --1 - --x 2 - -w3 - -wx 4 - r— 5 - r-x 6 - rw7 – rwx
Tip: The easiest way to set the permissions is to right click on the file or directory in WinSCP, select properties. You can then tick the permission you want to allow.
14.3 Chown In addition to the file permission, you can also modify the owner and group of the file. The chown program is used here and its syntax is very simple. You need to be the owner of a file or root to do this. chown new-owner somefile Or to change the owner and the group recursively # chown –R Group:Owner /path/to/directory
14.4 chgrp To change group, user the chgrp command. Syntax is similar to chown. You will need to be the owner of the file and also belong to the same group as the file, or you should be root. chgrp new-grp somefile
15 Services Services on a Linux system are often known as Daemons. They typically run in the background and are launched at boot time.
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Typically, daemons end with a d as in sshd for the SSH service or Daemon. Services can be stopped, started, restarted and the status queried:Service <
15.1 # chkconfig To start services automatically at boot time, the chkconfig command is used. However, we need to know which run level is used. Normally this is three for our purposes. The run levels for CentOS are as follows: -
0 - Halt 1 - Single user 2 - Not used/User definable 3 - Full multi-user, console logins only 4 - Not used/User definable 5 - Full multi-user, with display manager as well as console logins 6 - Reboot
So if we want the SSH server to run in levels 3, 4 and 5 we would type: # chkconfig --level 345 sshd on to turn it off:# chkconfig --level 345 sshd off In order to discover what services are running type # chkconfig –list
15.2 /etc/rc.d/rc.local This file is like the windows startup folder. Processes and scripts can be launched from here at the end of the boot process.
15.3 Stopping services and processes. Usually an active session, such as a find, which is taking a long time can be stopped pressing CTRL C
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However sometimes, it is impossible to stop a service, so something more dramatic has to be used. This is the Linux equivalent of CTRL-ALT-DEL in Windows The first thing to discover is the process ID, or the PID.
15.4 # ps aux Shows a list of running processes, with the PID and some other metrics
15.5 # kill Kills the process. Kill 235 where 235 is the PID to kill
15.6 # kill -9 Force kills the process kill -9 235 force kills the PID
15.7 # top Shows the running processeswith the most processor intensive at the top. This displays in real-time.
16 Reboot and shutdown
16.1 # reboot Reboots the Server
16.2 # shutdown –h now Usage: message]
shutdown [-akrhHPfnc] [-t secs] time [warning -a: use /etc/shutdown.allow -k: don't really shutdown, only warn. -r: reboot after shutdown. -h: halt after shutdown. -P: halt action is to turn off power. -H: halt action is to just halt. -f: do a 'fast' reboot (skip fsck). -F: Force fsck on reboot. -n: do not go through "init" but go down real fast. -c: cancel a running shutdown. -t secs: delay between warning and kill signal. ** the "time" argument is mandatory! (try "now") **
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17 Pipe
17.1 # | The pipe command allows the output of one command to be piped into the input of another command.
17.2 Redirect Output The > symbol redirects output from a command to another destination such as a file so you can analyse the contents at your leisure. e.g. ls –al > list.txt willl send the output of ls –al to a the text file; list.txt
17.3 # > Appends to the end of an existing file.
17.4 ## >> Clears the file first. 18 Compression
In order to compress a file, or amalgamate a large number of files into one large file, the following commands can be used, or a directory or file can be compressed using the WinSCP utility. Strictly speaking, TAR, derived from tape archive is not really used for compression. The same extraction command will work. Note that unTAR’ing a TAR file extracts the files into the same directory tree in which they were stored beginning at the location from which the command is executed. Thus, if /var/myfile.txt is included in the archive, then extracting the archive from the root directory would place the file in /var while extracting the archive from /junk would place the file in /junk/var. There's another beauty and curse to tarballs. They preserve the ownership and permissions of the original files which are included in the archive. This includes the ownership and permissions of the original directory structure as well. If you are creating a tarball, be mindful of the consequences of creating a
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tarball with a directory structure with ownership and permissions which may differ from those on target systems. Creating a Tarball is a two stage process. First all the files are put into a TAR file, and then they are compressed using a compression utility such as Gzip or Bzip.
18.1 # tar Strictly speaking, TAR, derived from the words Tape ARchive is not really used for compression. It simply rolls a number of files into one big file (Tarball) The most popular command is tar –zxfv filename.tar.gz to extract the files from an existing archive. To archive and compress a file the following sequence is used: tar -cf filename.tar /etc/myfile.conf /var/lib/asterisk/agibin/somefile.php We can check that the tarfile is acceptable by executing tar -tf filename.tar Then we compress the tar file with: gzip filename.tar This returns a file called filename.tar.gz. .tar.gz and .tgz are used interchangeably Tip: For untarring a file, do it from the command line – tar zxfv filename.tar.gz. To tar and compress a file, it is easiest, and less prone to error if you do it from within WinSCP. Select the directories to be compressed, rightclick and select Tar.
18.2 # gzip As above
18.3 # bzip bzip –czvf filename.tar filename but using the bzip compression algorithm
18.4 # zip & unzip If a compressed file ends with the zip extension, use unzip to decompress.
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19 Networking In order to set up a machine on a network, you will need the following information. -
The IP address Netmask Gateway DNS server
Please note that the command netconfig has been deprecated, which is a fancy way of saying they’ve replaced it with something else.
19.1 # ifconfig Shows the current IP addresses of every interface, note that a physical interface can have more than one IP address.
19.2 # system-config-network A text based GUI to set the IP address of any interface. This utility writes to:/etc/sysconfig/network-scripts/ifcfg-eth0 in the case of network interface known as eth0. It can be manually edited if necessary. With a fixed IP address the file should look like this:DEVICE=eth0 ONBOOT=yes BOOTPROTO=static IPADDR=192.168.3.200 NETMASK=255.255.255.0 GATEWAY=192.168.3.254 Type service network restart to set the changes. Be careful you do not lock your self out with a typing error.
19.3 # resolv.conf The file containing the details of how to resolve an domain name to an IP address. To add a nameserver, type nano –w /etc/resolv.conf and add the line: Nameserver 1.2.3.4 Where 1.2.3.4 is the DNS server. Often, but not always, the gateway/router doubles up as the DNS Server
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Ping some internet domain names in order to check that DNS resolution is working.
19.4 # hostname Sets the name of the server.
19.5 # ifdown Stop the interface, e.g. ifdown eth0
19.6 # ifup Bring the interface back up again.
19.7 # ping Send a packet to a host and measure the time it takes to make the round trip. E.g. ping www.google.com
19.8 # traceroute Trace the route to a host. E.g. traceroute www.google.com
19.9 # mtr mtr is a very useful command combining ping and traceroute in the same command. It shows the live status of the path to a host. E.G. mtr www.google.com
20 Network Security There is no substitute for having a good firewall, but Linux contains IP tables that filter and manipulate packets. 20.1.1
Iptables IP tables are are found in /etc/sysconfig/iptables they can be managed by hand editing them, or it is much easier via Webmin. Open Webmin and navigate to Networking then Linux Firewall.
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21 Installing software There are a number of ways of getting software on the server, the following are methods are described below.
21.1 Compiling from source In many cases, programs can be compiled from source. That is to say that there is machine readable source code, and using development tools on the server, software can be compiled and installed. Generally, the software is untarred to /usr/src/<packagename>. Within the unzipped directory will be a readme file, or install.txt which should be read before proceeding to see if there is anything special that needs to be done. In general, the commands are as follows:21.1.1
# make clean Clean up any failed or previous installs. # ./configure
21.1.2
Checks and configures the package ready for compiling and installation, and ensures that all the dependencies are in place. If the there is hardware to be installed, there is a very good chance that you will need the kernel sources. (yum install kernel-devel) Watch the output for any errors. If there are dependencies missing, then these may have to be installed first, probably from the yum repositiory 21.1.3
# make Compile the program.
21.1.4
# make install Install the program
21.2 # yum Use the CentOS repository, and other repositories to install and update software. E.g.
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# Yum update updates the entire operating system. Note that if any hardware has been compiled against the kernel, ie.zaptel, then the package will have to recompiled as above. # yum search <package name> search for a package. # yum install <package name> # yum –y install <package name> ; installs programs without any further prompts.
21.3 # rpm Many programs, e.g. webmin come as an rpm, or a precompiled binary, so that the program does not have to be compiled on the machine. The usual command is rpm –iv <package name> If the package is available on the yum repository, it is usually better to install it from there. The RPM package may not be specific to your own Linux distribution.
22 Logs
There are a large number of logs on the system, which can give good information on any problems, who has accessed the machine, and what they have done with them. To view them, you can use less, tail, cat, and other similar commands as listed above. A few of the more important logs are below.
22.1 /var/log/messages Contains general system logging
22.2 /var/log/dmesg Contains hardware loading information
22.3 /var/log/asterisk/full Contains the Asterisk log file
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22.4 # logrotate Logs can get quite large, so it is important to do some housekeeping to ensure that the file system does not become full. This is usually done for you. But if not, read the man logrotate. 23 Crontab The crontab is a way of making timed events happen on a regular basis. They are also known as cron jobs. Cron jobs are easiest set up in Webmin. Crontabs can also be viewed and edited using crontab command at the command line. Once in crontab, the editing commands are the same as Vi editor, which is another text editor supplied with Linux, and is about as user friendly as a cornered rat. So I would urge you to use webmin for adding and editing. 24 Users and Groups
24.1 Users Users are people, and processes that have access to things on the system
24.2 Groups A group is a collection of users to make administration easier.
24.3 # sudo It is not necessarily desirable to have root as the main access to system. If hackers get access to the system, they can go everywhere. Additionally, it is possible to make a mistake on the system. By being a non root user, some of these mistakes can be mitigated. To set up a sudo user:# adduser myusername # passwd myusername <password>
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To edit the sudoers file to run sudfo commands, nano /etc/sudoers and add the following line: myusername ALL=(ALL) ALL Now simply execute commands as the root user by typing sudo
25 Network Services The server runs a few of the following services.
25.1 NTP A time server. Linux can get its time from the internet, and act as a time server for devices on your network. For this to happen, ntpd must be running (service ntpd status) and port 123 udp must be open on the firewall To force the computer to set the right time. # service ntpd stop # ntpdate 1.pool.ntp.org # service ntpd start Tip: Before commencing the installation of Linux, check that the hardware clock in BIOS is set to the right time and date, otherwise installation of packages may fail.
25.2 DNS Domain Name resolution. Linux can be a domain name server. The easiest way to set this up is in webmin. Click on servers, then Bind.DNS Server, and set it up with the default values offered by Webmin. Port 53 must be open to allow DNS queries
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25.3 DHCP DHCP, Dynamic Domain Name Server. Port 67 UDP must be open to deliver IP addresses to it clients. This can be set up and started in Webmin easily. If you wish to run a DHCP server on your machine, ensure that you start it as a service. Refer to chkconfig instructions above.
25.4 TFTP A TFTP server is what a phone and other devices use to get their configuration. Run these commands to get it running: # yum -y install tftp-server # /sbin/chkconfig --level 345 xinetd on # /sbin/chkconfig --level 345 tftp on # service xinetd restart To check it is running: netstat -nulp|grep 69
You should see a result that includes a line that looks similar to the following: udp 0 0 0.0.0.0:69 0.0.0.0:* 25.4.1
Option 66 Option 66 in the DHCP configuration is the setting that tells TFTP enabled devices where to find the TFTP server.
25.5 Sendmail / Postfix These programs are both popular programs for sending mail. To set them up the way you want them. Webmin is the best option for those with Conversational Linux
25.6 Apache The web server, that delivers web pages. The Daemon is called httpd. To restart apache, type httpd –k restart In general, the /var/www/html.
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25.7 PHP PHP is a language that when combined with Apache and MySQL allows interactivity with the web page. Adding, removing and displaying records from a database.
25.8 MySQL MySQL is one of the most popular database systems. It can handle many millions of records. If you have Apache and PHP installed, the database can be viewed via phpMyAdmin. See www.phpmyadmin.net. Do however note the licensing of MySQL. It is undergoing change due to a commercial buyout. 26 Hardware
26.1 # lspci Show the interrupts on the system, add –v for more information
26.2 # cat /proc/interrupts As above, but from a different source 27 SSH Tunnelling SSH has the ability to tunnel connections from your PC to any other IP address that the CentOS server has access to. This can be useful for reconfiguring routers or phones on the remote network. In putty, open a connection to the remote server. Once connected, click on the little icon in the top left hand corner of putty and select “Change Settings” In the left hand side bar, select Connection, SSH, Tunnels And you should end up with a screen like this: -
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27.1 Example One Assume that we want to connect to the router which is on 192.168.3.254 using port 80. Fill in the boxes as follows: •
Source port = 80
•
Destination port = 192.168.3.254:80
•
Leave Local and Auto as the defaults
Click add, then apply On your local browser, Firefox or Internet Explorer, type http://localhost and the router will appear in your web page.
27.2 Example Two You wish to connect to a number of phones on the network, that are on 192.168.3.201, 202, 203 etc, to match the extension numbers, 201, 202, 203 etc. You can add a number of tunnels, so to connect to 192.168.3.201 •
Source Port = 201
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•
Destination – 192.168.3.201:80
•
Click add, then add the next phone
•
Source Port = 202
•
Destination = 192.168.3.202:80
Click Add, and continue in this manner. When you have added all your phones, click Apply. •
To access extension 201, type http://localhost:201
•
To access extension 202, type http://localhost:202
Ports 201 and 202 were only chosen to make it easy to remember where to find the phones. Any source port can be chosen
28 Conclusion Now you have read this document, you should have enough information and tools to be able to do basic Linux installs, configuration and maintenance, as well as search for further information should you need to. The purpose of the above is not to give you a complete overview of Linux, but just enough to get you started, and carry out basic commands with an understanding of what you are doing in the context of installing a PBX.
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