Solaris run levels

Solaris init states refer to the services provided by the system. The exact services and processes run at each init level are determined by the scripts in the /etc/rc#.d directories. The default service levels for each init state are:

• 0: The system is at the security monitor (>) prompt. It is safe to shut down the system when it is at this init state.
• 1, s or S: This state is known as "single-user" or "system administrator" mode. Root is the only user on the system, and only basic kernel functions are enabled. A limited number of filesystems (usually only root and /usr) are mounted. This init state is often used for sensitive functions (such as kernel libc patches) or while troubleshooting a problem that is keeping the system from booting into multiuser mode.
• 2: Multiple users can log in. Most system services (except for NFS server and printer resource sharing) are enabled.
• 3: Normal operating state. NFS and printer sharing is enabled, where appropriate.
• 4: Usually undefined.
• 5: Associated with the boot -a command. The system is taken to init 0 and an interactive boot is started.
• 6: Reboot. This state takes the system to init state 0 and then to the default init state (usually 3, but can be redefined in the /etc/inittab file).

To get to a desired run level n, each of the rc (run control) scripts from 1 to n is run. To get to run level 0, the K scripts are run in each rc#.d directory between the current run level and 0 in reverse numerical order.