Boot Process Tech

The Booting & Shutdown Process

Booting Phases • Boot strapping is the process a computer follows to load and execute the bootable operating system. • The boot process goes through the following phases: Boot PROM phase. Boot program phase. Kernel Inialialization phase. Init phase.

Boot PROM Phase • After you turn on power to the system, the PROM displays system identification information and runs self-test diagnostics to verify the system’s hardware and memory. • It then loads the primary boot program, called bootblk

Boot Program Phase • The bootblk program finds and executes the secondary boot program (called ufsboot) from the ufs file system and loads it into memory. • After the ufsboot program is loaded, it loads the kernel.

Kernel Initialization Phase •The kernel initializes itself and begins loading modules, using ufsboot to read the files. •When the kernel has loaded enough modules to mount the root file system, it unmaps the ufsboot program and continues, using its own resources. • The kernel starts the UNIX operating system, mounts the necessary file systems, and runs /sbin/init to bring the system to the “initdefault” state specified in /etc/inittab.

Init Phase • The Kernel creates a user process and starts the /sbin/init process, which starts other processes by reading the /etc/inittab file. • The /sbin/init process starts the run control (rc) scripts, which execute a series of other scripts. These scripts (/sbin/rc* check mount file systems, start various processes, and perform system maintenance tasks

Boot Command Options # boot -(one of the following options) -a An interactive boot -r A reconfiguration boot -s Boots into a single-user state -v Boots in verbose mode

System Run States Run state 0 Halt Run state S,s Single User (without users) Run state 1 Single User (with users) Run state 2 Multi User (without NFS) Run state 3 Multi User (with NFS) Run state 4 N/A Run state 5 Poweroff to SPARC Run state 6 Reboot

Run State 0 • Stops system services and daemons. • Terminates all running processes. • Unmounts all file systems.

Run state S,s • Single-user (system administrator) state. • Only root is allowed to log in at the console, and any users logged in are logged out when entering this run level. • All file systems previously mounted remain mounted and accessible. • All services except the most basic OS services are shut down in an orderly manner.

Run state 1 • Single-User (system administrator) state. • All file systems are still available, and any logged-in users can remain logged in. • All services except the most basic OS services are shut down in an orderly manner.

Run state 2 • • • • • • • • •

Normal multiuser operation without NFS file systems shared. Sets the time zone variable. Mounts the /usr file system. Cleans up the /tmp and /var/tmp directories. Loads the network interfaces and starts processes. Starts the cron daemon. Cleans up the uucp tmp files. Starts the lp system. Starts the sendmail daemon

Run state 3 • Normal multiuser operation of a file server with NFS systems shared. • Completes all the tasks in run level 2. • Starts the NFS system daemons.

Run state 4 • Alternative multiuser state (currently not used)

Run state 5 • Power-down state. • Shuts down the system so that it is safe to turn off power to the system. • If possible, automatically turns off system power on systems that support this feature.

Run state 6 •

Reboots

INIT Phase • The /sbin/init command generates processes to set up the system based on the directories in /etc/inittab. • The init process is the parent of all other processes. • It examines the contents of the /etc/initab file. id:runlevel:action:process id A unique identifier runlevel The run level action How the process is to be run. process The name of the command to execute

Inittab Action Fields powerfail wait Respawn

The system has received a powerfail signal Waits for the command to be completed. Restarts the command

System Shutdown /usr/sbin/shutdown /sbin/init /usr/sbin/halt /usr/sbin/reboot /usr/sbin/poweroff

/usr/sbin/shutdown • The shutdown command sends a warning message to all users who are logged in, waits for 60 seconds (the default), and then shuts down the system to single-user state. shutdown -i -g -y i Brings the system to an init state different from the default of S. The choices are 0,1,2,5, and 6. -g Indicates a time (in seconds) before the system is shut down. The default is 60 seconds. -y Continues to shut down the system without intervention; otherwise, you are prompted to continue the shutdown process after 60 seconds.

/sbin/init • Init command can be used to shutdown a single-user system or to change its run level. init

/usr/sbin/halt • The halt command shuts down the system without any delay. • It does not warn any other users on the system of the shutdown.

/usr/sbin/reboot • Reboot command can be used to shut down a single-user system and bring it into multiuser state. • Reboot does not warn other users on the system of the shutdown.

/usr/sbin/poweroff •

The poweroff command is equivalent to the init 5 command