Solved : Comparing Run Levels in Linux and Solaris and precautions withthem

Many people get confused between run levels in Linux and Solaris. One major difference among these can be disastrous also.  In this post we will show you the different Run levels in both these OS and what precautions you should take while working on these.
Let’s first take a look at Run levels.
Linux Run Levels

ID	Name	Description
0	Halt	No activity, System can be safely shut down.
1	Single-user mode	For administrative tasks only. Rarely used.
2	Multi-user mode	Multiple users but no NFS (Network File System).
3	Multi-user mode with networking	Multiple user but command line mode only.
4	Not used/user-definable	For special purposes. User definable.
5	Start the system normally with appropriate display manager (with GUI)	It’s similar to run level 3 but with GUI display.
6	Reboot	Reboots the system.

Solaris Run levels

ID	Name	Description
0	Power-down state	Power down state(OBP level after POST). Will bring server to OK prompt for maintenance.
s or S	Single-user state	To run as a single user with all file systems mounted and accessible. Only root user is allowed login.
1	Single User – Administrative state	To access all available file systems with user logins allowed.
2	Multi-user mode	Multiple users but no NFS(Network File System). i.e. all daemons running except NFS daemon.
3	Multi-user mode with networking	All daemons running including NFS with GUI.
4	Not used/user-definable	For special purposes. User definable.
5	Power-off	Shutdown gracefully. Difference from Level 0 is that you won’t get any OBP (OK) prompt in Level 5
6	Reboot	Reboots the system.

Precaution
Not sure if you have noticed but there is major difference in Run Level 5 of both the OS. For Linux, run level 5 means multi user with GUI, all good. But for Solaris, run level 5 means power-off, ouch! . Many Linux admins who start working on Solaris makes the mistake of executing “init 5” on Solaris to get the GUI but, that actually brings down a Solaris server. Hope you never make this mistake on production box.
Check current run level

who -r

Above command will tell  you the current level of your system.