Linux+ Unit 05

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Linux filesystem management Unit objectives  Explain the function of the Filesystem Hierarchy Standard  Find files and directories and link files  Modify file and directory ownership  Identify the default permissions and apply special file and directory permissions

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Topic A  Topic A: The Filesystem Hierarchy Standard  Topic B: Searching and linking files  Topic C: File and directory permissions  Topic D: Default and special permissions

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Filesystem Hierarchy Standard  Outlines standard locations for files and directories  Gives software developers a consistent context regardless of the distribution  Helps users of one system work on another

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Linux directories defined by FHS

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FHS: Linux directories

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Activity A-1

Discussing the FHS directory structure

Managing files and directories Course ILT

 mkdir command – Takes arguments specifying the absolute or relative pathnames of the directories to create

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Activity A-2

Creating new directories

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Managing files and directories  The mv command requires two arguments at a minimum: – Source file/directory – Target file/directory

continued

Managing files and directories, continued

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 cp command – Command used to create copies of files and directories

continued

Managing files and directories, continued

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 rm command – Takes a list of arguments specifying the absolute or relative pathname of files to remove

continued

Managing files and directories, continued

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 rmdir command – Command used to empty directories

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Activity A-3

Moving files by using the mv command

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Activity A-4

Copying files by using the cp command

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Activity A-5

Using the rm and rmdir commands

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Topic B  Topic A: The Filesystem Hierarchy Standard  Topic B: Searching and linking files  Topic C: File and directory permissions  Topic D: Default and special permissions

Finding files Course ILT

 locate command – Fastest method to search for files – A shortcut to the slocate (or secure locate) command

 find command – Used to find files using various criteria – Searches the directory tree recursively, starting from a certain directory, for files that meet criteria

which command and PATH variable

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 which command – Used to locate files within directories listed in the PATH variable

 PATH variable – Stores list of directories searched when commands are executed without an absolute or relative pathname

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Activity B-1

Using find, locate, and which commands

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Linking files  On a structural level, a filesystem has three main sections: – The superblock – The inode table – Data blocks

 Files can be linked two ways – Symbolic link or symlink, one file a pointer or a shortcut to another file – Hard link, two files share the same data

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Structure of hard linked files

In command Course ILT

 ln (link) command – Command used to create hard and symbolic links

 To create hard link use the ln command with two arguments: – The existing file to hard-link – The target file that will be created as a hard link to the existing file

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Structure of symbolically linked files

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Activity B-2

Making and viewing links to files and directories

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Topic C  Topic A: The Filesystem Hierarchy Standard  Topic B: Searching and linking files  Topic C: File and directory permissions  Topic D: Default and special permissions

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File and directory permissions  When a user creates a file or directory, that user’s name and primary group become the owner and group owner of the file  Primary group – Default group to which a user belongs

chown and chgrp commands Course ILT

 chown (change owner) command – Used to change the owner and group owner of a file or directory

 chgrp (change group) command – Change the group owner of a file or directory – Takes two arguments at a minimum:  The new group owner  The files or directories to change

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Activity C-1

Using chown and chgrp

Managing file and directory permissions

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 Mode – The section of the inode that stores permissions – Divided into three sections based on the user(s) that receive(s) the permission to that file or directory  User (owner) permissions  Group (group owner) permissions  Other (everyone on the Linux system) permissions

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Regular permissions  There are three regular permissions that you might assign to a user – Read – Write – Execute

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The structure of a mode

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Interpreting permissions

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chmod command  Used to change the mode (permissions) of a file or directory  Takes two arguments at a minimum: – The first specifies criteria used to change permissions – The remaining arguments indicate the filenames to change

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Criteria used: chmod command

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Mode: numeric representation

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Numeric representations: permissions

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Activity C-2

Applying and modifying access permissions

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Topic D  Topic A: The filesystem hierarchy standard  Topic B: Searching and linking  Topic C: File and directory permissions  Topic D: Default and special permissions

Default permissions Course ILT

 umask – Used to alter the permissions on all new files and directories – Takes select default file and directory permissions away – Applies only to newly created files and directories  Never used to modify existing files or directories

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umask 022 calculation

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umask 007 calculation

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Activity D-1

Using the umask variable

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Special permissions  Three special permissions that you can use on files and directories: – SUID (Set User ID) – SGID (Set Group ID) – Sticky bit

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Defining special permissions  The SUID has no special function when set on a directory – However, if the SUID is set on a file and that file is executed, then the person who executed the file temporarily becomes the owner of the file while it is executing

 The SUID can be applied only to binary compiled programs

continued

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Defining special permissions, continued

 The SGID has a function when applied to both files and directories  The SGID allows regular users to execute a binary compiled program and become a member of the group that is attached to the file during execution of the program  The sticky bit performs a useful function only on directories

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Setting special permissions  The mode of a file that is displayed using the ls –l command does not have a section for special permissions  Special permissions require execute – They mask the execute permission when displayed using the ls –l command

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Special permissions in the mode

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Absence of execute permissions

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Numeric representation

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Activity D-2

Viewing and setting special permissions

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Unit summary  Explained the function of the Filesystem Hierarchy Standard  Found files and directories and linked files  Modified file and directory ownership  Identified default permissions and applied special file and directory permissions