『Linux』/etc/inittab
作者：互联网
文章目录
inittab文件简介
/etc/inittab文件是Linux初始化系统使用的配置文件，在不同发行版Linux的位置不同，本文使用RedHat 9研究
#
# inittab This file describes how the INIT process should set up
# the system in a certain run-level.
#
# Author: Miquel van Smoorenburg, <miquels@drinkel.nl.mugnet.org>
# 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
inittab控制着系统boot和更改runlevel时所执行的代码。在我们按下电源键时，此文件就会指导系统工作
inittab文件内容
该文件定义了以下三项：
- default runlevel
- what processes to start, monitor, and restart if they terminate
- what actions to take when the system enters a new runlevel
简而言之：该文件定义了默认运行等级、每个运行等级下的操作，以及进程启动、监视、重启。
一旦inittab文件中关于运行等级的所有操作执行完成，便代表了boot完成，之后就引导进入登录界面，用户可以使用账户密码登陆进入系统
配置文件中的各项操作以id:runlevel:action:process构成
- id: 识别功能
- runlevel: 适用的运行等级
- action: 指挥init如何处理操作，可选
initdefault, sysinit, boot, bootwait, wait, respawn - process: 定义了要执行的命令或脚本
Default Runlevel
以下是linux默认运行等级及其解释：
# 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:
- 关机
- 单用户模式
- 多用户模式（无NFS）
- 完全多用户模式
- 保留未使用
- X11多用户模式（GUI）
- 重启
注释特别说明：请勿将默认启动等级设置为0和6，这将会无法引导boot启动！
之后是当前系统的默认运行状态，当前设置为XWindows模式，启动将会进入GUI
System Initialization
接下来一行定义了无论哪个等级启动，初始化系统都会执行/etc/rc.d/rc.sysinit
si::sysinit:/etc/rc.d/rc.sysinit
一旦系统运行了rc.sysinit，它将从下面的选择默认运行等级对应的代码行，并运行/etc/rc.d/rc脚本
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
process指定了运行的脚本都是/etc/rc.d/rc，唯一区别就在传参是对应的runlevel
runlevel作为参数传入rc，rc执行/etc/rcN.d，N是runlevel
for i in /etc/rc$runlevel.d/S* ; do
查看当前选中的/etc/rc.d/rc5.d目录，发现全是各种启动服务的脚本：
[root@localhost root]# ls /etc/rc5.d
K05innd K20rwhod K46radvd K74ntpd S08ipchains S56xinetd
K05saslauthd K24irda K50netdump K74ups S08iptables S57vmware-tools-thinprint
K09privoxy K25squid K50snmpd K74ypserv S09isdn S59hpoj
K10psacct K28amd K50snmptrapd K74ypxfrd S10network S80sendmail
K12mailman K34dhcrelay K50tux K84bgpd S12syslog S80spamassassin
K12mysqld K34yppasswdd K50vsftpd K84ospf6d S13irqbalance S85gpm
K15httpd K35atalk K54pxe K84ospfd S13portmap S90canna
K15postgresql K35dhcpd K55routed K84ripd S14nfslock S90crond
K16rarpd K35smb K61ldap K84ripngd S17keytable S90cups
K20bootparamd K35vncserver K65identd K85zebra S20random S90FreeWnn
K20iscsi K35winbind K65kadmin K90isicom S24pcmcia S90xfs
K20netdump-server K36lisa K65kprop K95firstboot S25netfs S95anacron
K20nfs K40mars-nwe K65krb524 S00microcode_ctl S26apmd S95atd
K20rstatd K45arpwatch K65krb5kdc S03vmware-tools S28autofs S97rhnsd
K20rusersd K45named K70aep1000 S05kudzu S55sshd S99local
K20rwalld K45smartd K70bcm5820 S08ip6tables S56rawdevices S99mdmonitor
- 以K开头代表kill
- 以S开头代表start
系统会运行K开头的脚本以杀死指定进程服务，然后运行S开头的脚本试图启动可能被关闭了的进程服务
Trap CTRL-ALT-DELETE
这个字段定义了快捷键CTRL+ALT+DELETE用以关机
ca::ctrlaltdel:/sbin/shutdown -t3 -r now
Powerfail Condition
以下是处理电源故障的代码：
# 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"
# 当UPS通知电源已经失效时，假设还有几分钟的电量储备，准备从现在开始的2分钟内关机。
# 当然，这是在假定已经安装了powerd，并且UPS已经连接并正常工作。
# 如果在关机之前电源已经恢复了，那就取消关机操作。
正如注释所示，这一段代码是用于处理UPS电源故障
Run Gettys
以下代码用以生成6个mingetty进程，且这六个进程被kill后还会respawn
# 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
只有关键进程被设置成这种方式，以保证它们不受系统中其他事情的影响。
下面代码保证了在runlevel-5启动时，保护X display manager无法被kill
# Run xdm in runlevel 5
x:5:respawn:/etc/X11/prefdm -nodaemon
因此：可以通过修改rcN.d来做到客制化kill和start，以满足用户的需求
init 0/6 与 shutdown/reoot
在Terminal可以使用init 0与init 6来关机和重启，那么和shutdown now、reboot有区别吗?
先看看这两个runlevel具体运行了什么脚本
[root@localhost root]# ls /etc/rc0.d
K03rhnsd K16rarpd K35atalk K50vsftpd K74ups K91isdn
K05anacron K20bootparamd K35dhcpd K50xinetd K74ypserv K92ip6tables
K05atd K20iscsi K35smb K54pxe K74ypxfrd K92ipchains
K05innd K20netdump-server K35vncserver K55routed K75netfs K92iptables
K05keytable K20nfs K35winbind K60crond K80random K95firstboot
K05saslauthd K20rstatd K36lisa K61hpoj K84bgpd K95kudzu
K09privoxy K20rusersd K40mars-nwe K61ldap K84ospf6d K96pcmcia
K10cups K20rwalld K43vmware-tools-thinprint K65identd K84ospfd K99mdmonitor
K10psacct K20rwhod K44rawdevices K65kadmin K84ripd K99microcode_ctl
K10xfs K24irda K45arpwatch K65kprop K84ripngd K99vmware-tools
K12canna K25squid K45named K65krb524 K85zebra S00killall
K12FreeWnn K25sshd K45smartd K65krb5kdc K86nfslock S01halt
K12mailman K28amd K46radvd K70aep1000 K87irqbalance
K12mysqld K30sendmail K50netdump K70bcm5820 K87portmap
K15gpm K30spamassassin K50snmpd K72autofs K88syslog
K15httpd K34dhcrelay K50snmptrapd K74apmd K90isicom
K15postgresql K34yppasswdd K50tux K74ntpd K90network
[root@localhost root]# ls /etc/rc6.d
K03rhnsd K16rarpd K35atalk K50vsftpd K74ups K91isdn
K05anacron K20bootparamd K35dhcpd K50xinetd K74ypserv K92ip6tables
K05atd K20iscsi K35smb K54pxe K74ypxfrd K92ipchains
K05innd K20netdump-server K35vncserver K55routed K75netfs K92iptables
K05keytable K20nfs K35winbind K60crond K80random K95firstboot
K05saslauthd K20rstatd K36lisa K61hpoj K84bgpd K95kudzu
K09privoxy K20rusersd K40mars-nwe K61ldap K84ospf6d K96pcmcia
K10cups K20rwalld K43vmware-tools-thinprint K65identd K84ospfd K99mdmonitor
K10psacct K20rwhod K44rawdevices K65kadmin K84ripd K99microcode_ctl
K10xfs K24irda K45arpwatch K65kprop K84ripngd K99vmware-tools
K12canna K25squid K45named K65krb524 K85zebra S00killall
K12FreeWnn K25sshd K45smartd K65krb5kdc K86nfslock S01reboot
K12mailman K28amd K46radvd K70aep1000 K87irqbalance
K12mysqld K30sendmail K50netdump K70bcm5820 K87portmap
K15gpm K30spamassassin K50snmpd K72autofs K88syslog
K15httpd K34dhcrelay K50snmptrapd K74apmd K90isicom
K15postgresql K34yppasswdd K50tux K74ntpd K90network
可以发现这两个脚本都是在最后的基础上提前kill了进程，因此二者的效果与shutdown now、reboot是相同的
参考
From:
networkworld: unix-how-to-the-linux-etc-inittab-file
geek-university: etc-inittab
serverfault: what-is-the-difference-between-init-6-and-reboot-on-red-hat-rhel-centos
完
标签：sbin,respawn,Linux,inittab,etc,rc,runlevel,wait 来源： https://blog.csdn.net/Xxy605/article/details/117291423