Solaris run levels

Solaris system state or init states refer to the level of services provided by the system on that specific run-level.Normally SVR4 systems has 7 run levels and Solaris too has that.

(S)tart files, (K)ill files:

In unix ,runlevel will define what are the process need to start in OS startup according to which run level defined in the /etc/inittab file.For example, in initab if the run-level mentioned as 3 then the system will start all the start scrips under rc1.d,rc2.d,rc3.d during the system boot.The files which are staring with “S” will start the process .When system is going down it will execute “K” scripts according to which init command you have used it.

Run Levels-Solaris

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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 server daemons.
3	Multiuser level with NFS resources shared	Multiuser	For normal operations with NFS resources shared. This is the default run level.
4	Alternative multiuser state		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 resources shared (or whatever level is the default in theinittab file).

Thanks to http://docs.oracle.com

To check current run level in Solaris type the below command.

bash-3.00# who -r

. run-level 3 Jul 16 01:44 3 0 S

run-level 3 – Identifies the current run level
Jul 16 01:44 – 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

Like everything else in a Solaris system, run levels are defined by files in the filesystem. All the run level files are found in the /etc directory according to the following table:
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Directoy and runlevels
/etc/rc0.d Run level 0
/etc/rc1.d Run level 1
/etc/rc2.d Run level 2
/etc/rc3.d Run level 3
/etc/rc4.d Run level 4
/etc/rc5.d Run level 5
/etc/rc6.d Run level 6

From Solaris 10 onwards,
The /etc/inittab file controls the configuration of init; for more information refer to init and inittab. It is no longer necessary to edit inittab directly; administrators should use the
Solaris Service Management Facility (SMF) to define services instead. Refer to smf and the System Administration Guide for more information on SMF.

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.

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

From oracle documentation. http://docs.oracle.com

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