Run Levels

A system's run level (also known as an init state) defines what services and resources are available to users. A system can be in only one run level at a time.

The release has eight run levels, which are described in the following table. The default run level is specified in the /etc/inittab file as run level 3.

Table 1-2 Oracle Solaris Run Levels

Run Level	Init State	Type	Purpose
0	Power-down state	Power-down	To shut down the operating system so that it is safe to turn off power to the system.
s or S	Single-user state	Single-user	To run as a single user with some file systems mounted and accessible.
1	Administrative state	Single-user	To access all available file systems. User logins are disabled.
2	Multiuser state	Multiuser	For normal operations. Multiple users can access the system and all file system. All daemons are running except for the NFS and SMB server daemons.
3	Multiuser level with NFS resources shared	Multiuser	For normal operations with NFS and SMB resources shared. This is the default run level.
4	Alternative multiuser state	Multiuser	Not configured by default, but available for customer use.
5	Power-down state	Power-down	To shut down the operating system so that it is safe to turn off power to the system. If possible, automatically turns off power on systems that support this feature.
6	Reboot state	Reboot	To shut down the system to run level 0, and then reboot to multiuser level with NFS and SMB resources shared (or whatever level is the default in the `inittab` file).

In addition, the svcadm command can be used to change the run level of a system, by selecting a milestone at which to run. The following table shows which run level corresponds to each milestone.

Table 1-3 Run Levels and SMF Milestones

Run Level	SMF Milestone FMRI
S	`milestone/single-user:default`
2	`milestone/multi-user:default`
3	`milestone/multi-user-server:default`

When to Use Run Levels or Milestones

In general, changing milestones or run levels is an uncommon procedure. If it is necessary, using the init command to change to a run level will change the milestone as well and is the appropriate command to use. The init command is also useful for shutting down a system.

However, booting a system by using the none milestone can be very useful when you are debugging startup problems. There is no equivalent run level to the none milestone. See How to Boot Without Starting Any Services for specific instructions.

Determining a System's Run Level

Display run level information by using the who -r command.

$ who -r

Use the who -r command to determine a system's current run level for any level.

Example 1-1 Determining a System's Run Level

This example displays information about a system's current run level and previous run levels.

$ who -r
 .    run-level 3  Dec 13 10:10  3  0 S
$

Output of `who` `-r` command	Description
`run-level 3`	Identifies the current run level
`Dec 13 10:10`	Identifies the date of last run level change
`3`	Also identifies the current run level
`0`	Identifies the number of times the system has been at this run level since the last reboot
`S`	Identifies the previous run level

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