PLD system can be run in several runlevels:
Runlevel 1 |
Single user mode. Used by administrator for rescue/emergency/system maintenance reasons. |
Runlevel 2 |
Multiuser level, but without Network File System |
Runlevel 3 |
Normal multiuser level. This is most commonly used runlevel. |
Runlevel 5 |
Normal multiuser level with X Window environment started by default. This is popular choice for workstations. |
Single |
Single user mode - used in emergency situations. It runs less services than runlevel 1. |
There are two more runlevels: these are Runlevel 0 and Runlevel 6. First one is used to bring all subsystems/processes down before system halt, second is used to accomplish similar task before system reboot.
System boots up in default runlevel that is defined in /etc/inittab which is usually 3 or 5. Current runlevel can be changed with telinit command. For example, if system is running level 3, issuing telinit 2 brings it to level 2 (as a consequence, NFS subsystems will be stopped).