Linux--系统运行级别
CentOS-6
| 级别 | 说明 |
|---|---|
| 0 | 关机 |
| 1 | 单用户模式(适用于root密码忘记，没有网络) |
| 2 | 多用户模式，但是没有NFS |
| 3 | 多用户模式，命令模式 |
| 4 | 没有使用 |
| 5 | 图形界面模式 |
| 6 | 重启 |
查看运行级别：
[root@localhost ~]# runlevel
N 3
修改运行级别：
- 临时切换：init 等级
- 永久切换：修改/etc/inittab文件
inittab文件内容：
[root@localhost ~]# cat /etc/inittab
# inittab is only used by upstart for the default runlevel.
#
# ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
#
# System initialization is started by /etc/init/rcS.conf
#
# Individual runlevels are started by /etc/init/rc.conf
#
# Ctrl-Alt-Delete is handled by /etc/init/control-alt-delete.conf
#
# Terminal gettys are handled by /etc/init/tty.conf and /etc/init/serial.conf,
# with configuration in /etc/sysconfig/init.
#
# For information on how to write upstart event handlers, or how
# upstart works, see init(5), init(8), and initctl(8).
#
# Default runlevel. The runlevels used 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:3:initdefault:
CentOS-7
inittab文件内容：
[root@localhost ~]# cat /etc/inittab
# inittab is no longer used when using systemd.
#
# ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
#
# Ctrl-Alt-Delete is handled by /usr/lib/systemd/system/ctrl-alt-del.target
#
# systemd uses 'targets' instead of runlevels. By default, there are two main targets:
#
# multi-user.target: analogous to runlevel 3
# graphical.target: analogous to runlevel 5
#
# To view current default target, run: # 查看运行级别可以运行:systemctl get-default命令
# systemctl get-default
#
# To set a default target, run: #设置运行级别可以使用:systemctl set-default TARGET.target命令
# systemctl set-default TARGET.target
#
查看所有运行级别的target：
[root@localhost ~]# ls -l /usr/lib/systemd/system/runlevel*target
lrwxrwxrwx. 1 root root 15 Oct 21 16:47 /usr/lib/systemd/system/runlevel0.target -> poweroff.target
lrwxrwxrwx. 1 root root 13 Oct 21 16:47 /usr/lib/systemd/system/runlevel1.target -> rescue.target
lrwxrwxrwx. 1 root root 17 Oct 21 16:47 /usr/lib/systemd/system/runlevel2.target -> multi-user.target
lrwxrwxrwx. 1 root root 17 Oct 21 16:47 /usr/lib/systemd/system/runlevel3.target -> multi-user.target
lrwxrwxrwx. 1 root root 17 Oct 21 16:47 /usr/lib/systemd/system/runlevel4.target -> multi-user.target
lrwxrwxrwx. 1 root root 16 Oct 21 16:47 /usr/lib/systemd/system/runlevel5.target -> graphical.target
lrwxrwxrwx. 1 root root 13 Oct 21 16:47 /usr/lib/systemd/system/runlevel6.target -> reboot.target
