running level

1. # 0 - halt (Do NOT set initdefault to this)

2. # 1 - Single user mode

3. # 2 - Multiuser, without NFS (The same as 3, if you do not have networking)

4. # 3 - Full multiuser mode

5. # 4 - unused

6. # 5 - X11

7. # 6 - reboot (Do NOT set initdefault to this)

init 0  #equal to halt
init 6  #equal to reboot

$cd /etc/rc.d
$ls
init.d  rc0.d  rc1.d  rc2.d  rc3.d  rc4.d  rc5.d  rc6.d  rc.local

Run a service(nginx) only in level 3 and 5

chkconfig nginx off
chkconfig --level 35 nginx on

Target vs RunLevel

Traditional runlevel      New target name     Symbolically linked to...

Runlevel 0           |    runlevel0.target -> poweroff.target
Runlevel 1           |    runlevel1.target -> rescue.target
Runlevel 2           |    runlevel2.target -> multi-user.target
Runlevel 3           |    runlevel3.target -> multi-user.target
Runlevel 4           |    runlevel4.target -> multi-user.target
Runlevel 5           |    runlevel5.target -> graphical.target
Runlevel 6           |    runlevel6.target -> reboot.target