Linux has 7 different run levels (or operating modes):
- 0 - System Halted
- 1 - Single User Mode
- 2 - Single User Mode with Networking
- 3 - Multi-User Mode - boot up in text mode
- 4 - Not yet Defined
- 5 - Multi-User Mode - boot up in X Windows
- 6 - Shutdown & Reboot
chkconfig is used to list all the registered services and display thier status at each different run level.
The runlevel command:
runlevel prints the previous and current SysV runlevel if they are known. The two runlevel characters are separated by a single space character. If a runlevel cannot be determined, N is printed instead. If neither can be determined, the word "unknown" is printed. Unless overridden in the environment, this will check the utmp database for recent runlevel changes. This is a legacy command available for compatibility only. It should not be used anymore, as the concept of runlevels is obsolete.
See also systemd(1), systemctl(1)