CentOS 7 之前的版本是通過 /etc/inittab 文件來定義系統運行級別:
[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 版本不再使用該文件定義系統運行級別,相關運行級別設置無效:
[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: #無效 [sywu@c1-11r2-rac1 etc]$
新版本的運行級別都定義在 /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
可以針對不同需要設置不同的運行級別:
如設置命令行級別(init 3)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
設置窗口級別(init 5)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
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修改系統運行級別：
1、systemd使用比sysvinit的運行級更為自由的target替代。第3運行級用multi-user.target替代。第5運行級用graphical.target替代。runlevel3.target和runlevel5.target分別是指向 multi-user.target和graphical.target的符號鏈接。
可以使用下面的命令切換到“運行級別3 ”：
systemctl isolate multi-user.target或systemctl isolate runlevel3.target
可以使用下面的命令切換到“運行級別5 ”：
systemctl isolate graphical.target或systemctl isolate runlevel5.target
2、如何改變默認運行級別？
systemd使用鏈接來指向默認的運行級別。在創建新的鏈接前，可以通過下面命令刪除存在的鏈接： rm /etc/systemd/system/default.target
默認啟動運行級別3 ：
ln -sf /lib/systemd/system/multi-user.target /etc/systemd/system/default.target
默認啟動運行級別5 ：
ln -sf /lib/systemd/system/graphical.target/etc/systemd/system/default.target
systemd不使用/etc/inittab文件。
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如何查看當前運行級別？
舊的runlevel命令在systemd下仍然可以使用。可以繼續使用它，盡管systemd使用 ‘target’ 概念(多個的 ‘target’ 可以同時激活)替換了之前系統的runlevel。
等價的systemd命令是systemctl list-units –type=target