CentOS 7 RunLevel Switch

Versions prior to CentOS 7 are defined by the/etc/inittab file to define the system RunLevel:

[Email protected] ~]$ cat/etc/centos-Release CentOS release6.4 (Final) [[email protected]~]$ cat/etc/Inittab#Inittab is a used by upstart for the default runlevel.##ADDING other CONFIGURATION, here would have the NO EFFECT on YOUR SYSTEM.##System initialization is started by/etc/init/rcs.conf##individual runlevels is started by/etc/init/rc.conf##Ctrl-alt-delete is handled by/etc/init/control-alt-delete.conf##Terminal Gettys is 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 is:#0-halt (do not set Initdefault to this)#1-single User Mode#2-multiuser, without NFS (the same as 3, if you don't have networking)#3-full Multiuser Mode#4-unused#5-x11#6-reboot (do not set Initdefault to this)#Id:3:initdefault:[[Email protected]~]$

The CentOS 7 version no longer uses this file to define the system RunLevel, and the associated run-level settings are invalid:

[Email protected] etc]$ cat/etc/centos-release CentOS Linux release7.0.1406(Core) [[email protected]-11r2-rac1 etc]$ cat/etc/Inittab # Inittab isNo longer used whenusingsystemd.## ADDING CONFIGURATION here would have NO EFFECT on YOUR system.## Ctrl-alt-delete isHandled by/etc/systemd/system/ctrl-alt-del.target## Systemd uses'Targets'Instead of Runlevels. Bydefault, there is the main targets:## multi-user.target:analogous to RunLevel3# graphical.target:analogous to RunLevel5# # toSetAdefaultTarget, run:## ln-sf/lib/systemd/system/<target name>.target/etc/systemd/system/default. Target#id:3: Initdefault: #无效 [[email protected]-11r2-rac1 etc]$

The new version of the runlevel is defined under/lib/systemd/system:

[Email protected] system]$ ls-ltr/lib/systemd/system/runlevel*lrwxrwxrwx.1Root root -July -  -: A/lib/systemd/system/runlevel1.targetrescue.targetlrwxrwxrwx.1Root root theJuly -  -: A/lib/systemd/system/runlevel0.targetpoweroff.targetlrwxrwxrwx.1Root root -July -  -: A/lib/systemd/system/runlevel2.target-multi-user.targetlrwxrwxrwx.1Root root -July -  -: A/lib/systemd/system/runlevel3.target-multi-user.targetlrwxrwxrwx.1Root root -July -  -: A/lib/systemd/system/runlevel4.target-multi-user.targetlrwxrwxrwx.1Root root -July -  -: A/lib/systemd/system/runlevel5.targetgraphical.targetlrwxrwxrwx.1Root root -July -  -: A/lib/systemd/system/runlevel6.target-Reboot.target

You can set different runlevel for different needs:

If you set the command line level (init 3) Method:

ln-sf/lib/systemd/system/runlevel3.target/etc/systemd/system/default-sf/lib/systemd/system/ multi-user.target/etc/systemd/system/defaultset-default multi-user.target

To set the window level (init 5) Method:

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

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To modify the system operating level:
1. SYSTEMD uses a more free target replacement than the Sysvinit run level. The 3rd run level is replaced with Multi-user.target. The 5th run level is replaced with Graphical.target. Runlevel3.target and Runlevel5.target are symbolic links that point to Multi-user.target and Graphical.target, respectively.
You can use the following command to switch to run Level 3:
Systemctl isolate Multi-user.target or Systemctl isolate Runlevel3.target

You can use the following command to switch to run Level 5:
Systemctl isolate Graphical.target or Systemctl isolate Runlevel5.target
2. How do I change the default runlevel?
SYSTEMD uses links to point to the default runlevel. Before creating a new link, you can delete the existing link by following the command: Rm/etc/systemd/system/default.target
Default startup Run Level 3:
Ln-sf/lib/systemd/system/multi-user.target/etc/systemd/system/default.target

Default startup Run Level 5:
Ln-sf/lib/systemd/system/graphical.target/etc/systemd/system/default.target

SYSTEMD does not use/etc/inittab files.

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How do I see the current runlevel?
The old RunLevel command can still be used under SYSTEMD. You can continue to use it, although SYSTEMD replaces the previous system's runlevel with the ' target ' concept (multiple ' target ' can be activated simultaneously).
The equivalent SYSTEMD command is Systemctl list-units–type=target

CentOS 7 RunLevel Switch