sysvinit runlevels
Halt (shutdown)
0
sysvinit runlevels
single user
1
sysvinit runlevels
multi-user (no n/w or remote file services)
2
sysvinit runlevels
full multi-user with n/w
3
sysvinit runlevels
unused
4
sysvinit runlevels
X11 graphical desktop mode
5
sysvinit runlevels
reboot
6