CST8177 - Linux II
booting, services, SysVinit 
Todd Kelley 
kelleyt@algonquincollege.com 

CST8177- Todd Kelley 

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.midterm 

.more booting 

.SysVinit 

.services     


 
     

2 
Today's Topics





.Power button pressed 

.BIOS 

.POST 

.MBR  : contains grub stage 1 

.grub stage 1 : to find grub stage 2 

.grub stage 2 : to launch kernel 

.kernel running 

.init process (PID 1) : consults inittab 

./etc/inittab 

./etc/init.d/rc.sysinit 

./etc/rc.d/rc 3   :  assuming default runlevel 3  



Booting Sequence (CentOS)
CST8177 - Todd Kelley 

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./etc/inittab contains records of the form 

.id:runlevels:action:process 

.id: identifies an entry 

.runlevels: the runlevels in which the action should be taken 

.action: the action that should be taken 

.process: the process to be executed 




/etc/inittab
CST8177 - Todd Kelley 
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.Some of the possible Actions: 

.respawn: process to be restarted whenever it terminates 

.wait: process to be started once, and init will wait for its termination 

.once: process executed once upon entering runlevel 

.boot: executed during system boot (runlevels ignored) 

.bootwait: executed during system boot, and init waits for its termination (runlevels ignored) 

.initdefault: runlevel to be entered on system boot (process ignored) 

.sysinit: executed before any boot or bootwait (runlevels ignored) 




/etc/inittab (cont'd)
CST8177 - Todd Kelley 

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.id:3:initdefault: 

.si::sysinit:/etc/rc.d/rc.sysinit 

.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  



CentOS /etc/inittab
CST8177 - Todd Kelley 
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.# consoles: virtual consoles CTRL-ALT-F(1-6) 

.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 

.# the X display manager (GUI) 

.x:5:respawn:/etc/X11/prefdm -nodaemon  



gettys and xdm
CST8177 - Todd Kelley 

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.# default runlevel 3 

./etc/init.d/rc.sysinit 

./etc/init.d/rc 3 



When booting
CST8177 - Todd Kelley 
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./etc/init.d/* 

.these are scripts for starting, stopping, restarting services 


./etc/rc.d/rc.N.d/*    #where N is a runlevel 

.these are symbolic links to service's script 

.begins with K means service should not be running in that runlevel: call it with "stop" argument 

.begins with S means service should be running in that runlevel: call it with "start" argument 


.chkconfig maintains these scripts 



SysVinit scripts
CST8177 - Todd Kelley 

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.all /etc/init.d/* scripts manageable by chkconfig have two or more commented lines 

.first tells chkconfig what runlevels, and start and stop priority 

.runlevels is "-" if by default should not be started in any runlevel 

.second is a description 

.For example: /etc/init.d/ntpd 

.# chkconfig: - 58 74 

.# description: ntpd is the NTPv4 daemon. \ 

.# The Network ....  



chkconfig
CST8177 - Todd Kelley 
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.The /etc/rc.d/rcN.d/ (N=0,1,2,3,4,5,6) directories contain symbolic links to scripts in /etc/init.d 

.These links are maintained by chkconfig 

.Upon entering runlevel 3 (for example): 

.each /etc/rc3.d/K* script is called with "stop" (if that service is running) 

.each /etc/rc3.d/S* script is called with "start" (if that service is not running) 

.The ordering of the scripts is given by the chkconfig priority, which is a number in the symlink name, that orders the scripts 




/etc/rc.d/rcN.d/*
CST8177 - Todd Kelley 

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.example /etc/rc3.d/S03vmware-tools 

.vmware-tools is configured to run in runlevel 3 

.otherwise, there would be a K99-vmware-tools script there instead 


.03 is the priority of starting vmware-tools service when entering that run level 


.This is a symlink to /etc/init.d/vmware-tools 



/etc/rc.d/rcN.d/*  (cont'd)
CST8177 - Todd Kelley 
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.service SCRIPT COMMAND [OPTIONS] 

.SCRIPT is /etc/init.d/SCRIPT 

.COMMAND is an argument to the script 

.start 

.stop 

.restart 

.etc 

.start and stop must be recognized by SCRIPT 


.Example: service ntpd start 

.same effect as /etc/init.d/ntpd start 


.Example: service ntpd stop 

.same effect as /etc/init.d/ntpd stop   




service - run a System V init script
CST8177 - Todd Kelley 

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