UNIX/LINUX 系統啟動方式INIT

UNIX/LINUX 系統啟動方式INIT簡單介紹

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init [option] [runlevel]
System administration command.
Option
-t seconds
When changing runlevels, send SIGKILL seconds after SIGTERM.
Default is 20.
Files
init is the first process run by any Unix machine at boot time. It verifies the
integrity of all filesystems and then creates other processes, using fork and
exec, as specified by /etc/inittab. Which processes may be run are controlled by
runlevel. All process terminations are recorded in /var/run/utmp and
/var/log/wtmp. When the runlevel changes, init sends SIGTERM and then, after
20 seconds, SIGKILL to all processes that cannot be run in the new runlevel.
Runlevels
The current runlevel may be changed by telinit, which is often just a link to
init. The default runlevels vary from distribution to distribution, but these are
standard:
0
Halt the system.
1, s, S
Single-user mode.
6
Reboot the system.
q, Q

Reread /etc/inittab.
Check the /etc/inittab file for runlevels on your system

[root@app ~]# more /etc/inittab
#
# 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:

# System initialization.
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

# Trap CTRL-ALT-DELETE
ca::ctrlaltdel:/sbin/shutdown -t3 -r now

# 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/shutdown -c "Power Restored; Shutdown Cancelled"

# 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