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System Administration Guide, Volume I

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 Solaris software environment has eight run levels, which are described in Table 6-1. The default run level is specified in the /etc/inittab file as run level 3.

Table 6-1 Solaris Run Levels

Run Level 

Init State 

Type 

Use This Level ... 

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 all file systems mounted and accessible.  

1 

Administrative state 

Single-user 

To access all available file systems with user logins allowed.

2 

Multiuser state 

Multiuser 

For normal operations. Multiple users can access the system and the entire file system. All daemons are running except for the NFS server daemons.

3 

Multiuser with NFS resources shared

Multiuser 

For normal operations with NFS resource-sharing available.

4 

Alternative multiuser state 

 

This level is currently unavailable. 

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 turn off system 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 state (or whatever level is the default in the inittab file).

How to Determine a System's Run Level

Display run level information by using the who -r command to determine a system's run level.


$ who -r

Use the who -r command to determine a system's current run level for any level except run level 0.

Example--Determining a System's Run Level


$ who -r
 .       run-level 3  Jun 10 09:56     3      0  S
$

run level 3

Identifies the current run level. 

Jun 10 09:56

Identifies the date of last run level change. 

3

Is the current run level. 

0

Identifies the number of times at this run level since the last reboot. 

S

Identifies the previous run level.