CentOS 7 运行级别切换

  CentOS 7 之前的版本是通过 /etc/inittab 文件来定义系统运行级别:

[sywu@wusuyuan ~]$ cat /etc/centos-release 

CentOS release 6.4 (Final)

[sywu@wusuyuan ~]$ 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:

[sywu@wusuyuan ~]$ 

CentOS 7 版本不再使用该文件定义系统运行级别,相关运行级别设置无效:

[sywu@c1-11r2-rac1 etc]$ cat /etc/centos-release 

CentOS Linux release 7.0.1406 (Core) 

[sywu@c1-11r2-rac1 etc]$ 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 /etc/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 set a default target, run:

#

# ln -sf /lib/systemd/system/<target name>.target /etc/systemd/system/default.target

#

id:3:initdefault:  #无效 [sywu@c1-11r2-rac1 etc]$ 

新版本的运行级别都定义在 /lib/systemd/system下:

[sywu@c1-11r2-rac1 system]$ ls -ltr /lib/systemd/system/runlevel*

lrwxrwxrwx. 1 root root 13 7月  30 14:22 /lib/systemd/system/runlevel1.target -> rescue.target

lrwxrwxrwx. 1 root root 15 7月  30 14:22 /lib/systemd/system/runlevel0.target -> poweroff.target

lrwxrwxrwx. 1 root root 17 7月  30 14:22 /lib/systemd/system/runlevel2.target -> multi-user.target

lrwxrwxrwx. 1 root root 17 7月  30 14:22 /lib/systemd/system/runlevel3.target -> multi-user.target

lrwxrwxrwx. 1 root root 17 7月  30 14:22 /lib/systemd/system/runlevel4.target -> multi-user.target

lrwxrwxrwx. 1 root root 16 7月  30 14:22 /lib/systemd/system/runlevel5.target -> graphical.target

lrwxrwxrwx. 1 root root 13 7月  30 14:22 /lib/systemd/system/runlevel6.target -> reboot.target

可以针对不同需要设置不同的运行级别:
如设置命令行级别方法:

ln -sf /lib/systemd/system/runlevel3.target /etc/systemd/system/default.target
或
ln -sf /lib/systemd/system/multi-user.target /etc/systemd/system/default.target
或
systemctl set-default multi-user.target

设置窗口级别方法:

ln -sf /lib/systemd/system/runlevel5.target /etc/systemd/system/default.target

或

ln -sf /lib/systemd/system/graphical.target /etc/systemd/system/default.target
或
systemctl set-default graphical.target