101 1.3 runlevels , shutdown, and reboot

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Text of 101 1.3 runlevels , shutdown, and reboot

  • 1. Junior Level Linux Certification

2. Exam Objectives Key Knowledge Areas Set the default runlevel. Change between run levels including single user mode. Shutdown and reboot from the command line. Alert users before switching runlevels or other major system event. Properly terminate processes. Objective 1: System Architecture Change runlevels and shutdown or reboot system Weight: 3 Terms and Utilities /etc/inittab shutdown init /etc/init.d telinit 2 3. Runlevels , shutdown, and reboot Runlevels 3 Runlevels define what tasks are accomplished in the current state (runlevel) of a Linux system. Every Linux system supports 3 basic runlevels, plus 1 or more runlevels for normal operation. Basic Linux runlevels Level Purpose 0 Shut down (or halt) the system 1 Single-user mode; usually aliased as s or S 6 Reboot the system Common Linux runlevels Level Purpose 2 Multiuser mode without networking 3 Multiuser mode with networking 5 Multiuser mode with networking and the X Window System - Slackware uses runlevel 4 for full system running X Window system. - Debian and Ubuntu, use a single runlevel for any multiuser mode, (runlevel 2) consult documentation for the distribution 4. Runlevels , shutdown, and reboot Default runlevel 4 When system starts, default runlevel is determined from id: entry in /etc/inittab. Ex: yourname@yourcomp~> grep "^id:" /etc/inittab id:5:initdefault: Entry for Fedora 8 or openSUSE 11.2, with runlevel 5 for the X Window System. 5. Runlevels , shutdown, and reboot Changing runlevels 5 To make a permanent change in runlevel, edit /etc/inittab and change the default level To make one boot in other runlevel (exemple: to edit the Linux System, or to install or build kernel modules). At boot time by editing the kernel cmdline in GRUB or add a parameter to LILO; Use a single digit to specify desired runlevel. each runlevel corresponds to scripts /etc/rc.d/rc?.d/S* (? for number 0 to 6). When theres change in runlevel, init runs a script which stops all extra processes in the current runlevel, and starts required processes from the new runlevel 6. Runlevels , shutdown, and reboot Changing runlevels 6 Ex 1: Changin runlevels at boot time - enter e command to edit. 7. Runlevels , shutdown, and reboot Changing runlevels 7 Ex 2: In menu with root, kernel, initrd - select kernel and press 'e' to edit 8. Runlevels , shutdown, and reboot Changing runlevels 8 Ex 3: In end of line - add space and digit runlevel '3'. Remove 'quiet' if you wish, or modify any other parameters if needed 9. Runlevels , shutdown, and reboot Changing runlevels 9 To change runlevel without rebooting the system. The command used is telinit. Use 1st the command runlevel to show previous runlevel and current one. If first output is 'N': the runlevel has not been changed since boot. Ex: yourname@yourcomp~> runlevel N 3 yourname@yourcomp~> telinit 4 Confirm the new runlevel after the change. Again with runlevel command Ex: yourname@yourcomp~> runlevel 3 4 10. Runlevels , shutdown, and reboot telinit and init 10 telinit is a symbolic link to init Since init runs as PID 1 at boot time the init executables know if the command invoked on prompt is the init or telinit and behaves accordingly. As a symbolic link: you may use init5 instead of telinit5 to switch to runlevel 5 or any other. Ex: yourname@yourcomp~> ls -l $(which telinit) lrwxrwxrwx 1 root root 4 2008-04-01 07:50 /sbin/telinit -> init 11. Runlevels , shutdown, and reboot Single-user mode 11 Single-user mode (runlevel 1)is selected to: Recover a filesystem or database, or install and test new hardware. System environment: shell with a minimal system; Usually without networking; Without daemons running (or very few); Goes straight into a shell prompt as root, or must log with authentication. Ex: yourname@yourcomp~> telinit 1 yourname@yourcomp~> telinit S Remember: telinit 1 or init switch to Single-user mode for admin will stop multiuser activity. Its a abrupt process - can cause users to lose work and processes to terminate abnormally. 12. Runlevels , shutdown, and reboot Clean shutdown 12 Preferred method to shut down or reboot the system is the shutdown command Process: 1.Sends warning message to all logged-in users and blocks any further logins. 2.Signals init to switch runlevels. 3. init process then sends all running processes a SIGTERM signal, giving them chance to save data and terminate properly. 4.After 5 sec, or another delay specified, init sends a SIGKILL signal to forcibly end each remaining process. By default, shutdown switches to runlevel 1 (single-user mode). Specify -h option to halt system, -r option to reboot. Standard message is issued in addition to any message you specify Shutdown time may be: Absolute in hh:mm format, Relative time in n (n=number minutes until shutdown) +0= Now Cancel delayed shutdown: press Ctrl-c or command shutdown -c. 13. Runlevels , shutdown, and reboot Clean shutdown 13 Ex: yourname@yourcomp~# shutdown 5 File system recovery needed Broadcast message from root (pts/1) (Tue Jan 4 08:05:24 2011): File system recovery needed The system is going DOWN to maintenance mode in 5 minutes! ^C Shutdown cancelled. yourname@yourcomp~# shutdown -r 10 Reloading updated kernel& [1] 18784 [yourname@yourcomp~# Broadcast message from root (pts/1) (Tue Jan 4 08:05:53 2011): Reloading updated kernel The system is going DOWN for reboot in 10 minutes! yourname@yourcomp~# fg shutdown -r 10 Reloading updated kernel ^C Shutdown cancelled. yourname@yourcomp~# shutdown -h 23:59& [1] 18788 [root@pinguino ~]# shutdown c Shutdown cancelled. [1]+ Done shutdown -h 23:59 14. Runlevels , shutdown, and reboot Clean shutdown 14 Ex: If time till shutdown exceeds 15 min., message is not sent until 15 minutes before the event. yourname@yourcomp~# date;shutdown -t60 17 Time to do backups& Tue Jan 4 08:12:55 EST 2011 [1] 18825 yourname@yourcomp~# date Tue Jan 4 08:14:13 EST 2011 yourname@yourcomp~# Broadcast message from root (pts/1) (Tue Jan 4 08:14:55 2011): Time to do backups The system is going DOWN to maintenance mode in 15 minutes! If shutdown is canceled, use wall command to send a warning to all users alerting them that the system is not going down. 15. Runlevels , shutdown, and reboot Halt, reboot, and poweroff 15 halt command: halts the system If any of these 3 commands are called when system is not in runlevel 0 or 6, then the corresponding shutdown command will be invoked instead. poweroff command: Is a symbolic link to halt command, which halts the system and attempts to power it off. reboot command: Is a symbolic link to halt command, which halts the system and then reboots it. 16. Runlevels , shutdown, and reboot inittab 16 When /sbin/init is started by kernel, it reads /etc/inittab for the startup sequence. The lines in /etc/inittab determine the startup behaviour of your system. Common inittab Actions Respawn Restart process whenever it terminates. Usually used for getty processes, that monitors logins. Wait Start process once when specified runlevel is entered and wait for its termination before init proceeds. once Start the process once when the specified runlevel is entered. Initdefault Specifies the runlevel to enter after system boot. ctrlaltdel Execute associated process when init receives the SIGINT signal. example: when someone on the system console presses CTRL-ALT-DEL. Common initab Format [id:runlevels:action:process] Id: unique identifier of one to four characters. Older versions limited to two characters. runlevels: lists runlevels for which action for this id should be taken. If no runlevels are listed, do action for all runlevels. action: describes which of several possible actions should be taken. process tells which process, if any, should be run when action on this line is performed. 17. Runlevels , shutdown, and reboot inittab 17 Ex: Part 1 ## inittab This file describes how the INIT process should set up # the system in a certain run-level. ## Author: Miquel van Smoorenburg, # Modified for RHS Linux by Marc Ewing and Donnie Barnes # # Default runlevel. The runlevels used by RHS are: # 0 - halt (Do NOT set initdefault to this) # 1 - Single user mode # 2 - Multiuser, without NFS (The same as 3, if you do not have networking) # 3 - Full multiuser mode # 4 - unused # 5 - X11 # 6 - reboot (Do NOT set initdefault to this) # id:5:initdefault: Before thinking runlevels, init runs the sysinit script. # System initialization. si::sysinit:/etc/rc.d/rc.sysinit 18. Runlevels , shutdown, and reboot inittab 18 Ex: Part 2 l0:0:wait:/etc/rc.d/rc 0 l1:1:wait:/etc/rc.d/rc 1 l2:2:wait:/etc/rc.d/rc 2 l3:3:wait:/etc/rc.d/rc 3 l4:4:wait:/etc/rc.d/rc 4 l5:5:wait:/etc/rc.d/rc 5 l6:6:wait:/etc/rc.d/rc 6 For actual runlevel chosen (before in id:5:initdefault), a script is run in this case /etc/rc.d/rc 5. Trap CTRL-ALT-DELETE ca::ctrlaltdel:/sbin/shutdown -t3 -r now Trapping Ctrl-Alt-Delete for keyboard system reboot. # Run gettys in standard runlevels 1:2345:respawn:/sbin/mingetty tty1 2:2345:respawn:/sbin/mingetty tty2 3:2345:respawn:/sbin/mingetty tty3 4:2345:respawn:/sbin/mingetty tty4 5:2345:respawn:/sbin/mingetty tty5 6:2345:respawn:/sbin/mingetty tty6 # Run xdm in runlevel 5 x:5:respawn:/etc/X11/prefdm -nodaemon In runlevel 2 ,3 , 4, 5, init verifies if the /etc/inittab as the following programs running: (mingetty handles terminal login, and mgetty handles modem dialin access) 19. Runlevels , shutdown, and reboot inittab 19 Ex: Part 3 # When our UPS tells us power has failed, assume we have a few minutes # of power left. Schedule a shutdown for 2 minutes from now. # This does, of course, assume you have powerd installed and your # UPS connected and working correctly. pf::powerfail:/sbin/shutdown -f -h +2 "Power Failure; System Shutting Down" # If power was restored before the shutdown kicked in, cancel it. pr:12345:powerokwait:/sbin/sh