Confusion In run level...

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Operating Systems Solaris Confusion In run level...
# 1  
Old 02-16-2008
Confusion In run level...

Dear Friends..!!

i am quit confused about the SOLARIES RUN level that is 0 . 1 or s S ...
please let me know the diffirence between these run level ... 0,1 and s S...

have a great day
Uday naikwadi
# 2  
Old 02-16-2008
First s == S; init accepts either upper or lower case s. The meaning of s is built into the init program itself. If init comes up in level s, /etc/inittab is ignored. If init had been in a numeric run level, init will transition down to a point where /etc/inittab is ignored. This is the original and official single user mode. It is the only mode that works if /etc/inittab is missing. While init is in level S, init will ignore requests to reread /etc/inittab. In level S, init would originally connect a shell to the system console so that commands can be entered. Some versions of init, including Sun's, have a change to connect the login program to the console. This change makes the system more secure, but now booting up to single user requires /etc/passwd and /etc/shadow. Some versions of init can do either behavior depending on the security level of the OS. But all of this is built in to init and cannot be changed by modifying /etc/inittab.

The numeric run levels are under the control of the author of /etc/inittab. Sun uses:

0 = firmware mode...OS will die and you get the "ok" prompt
1 = "administrative" mode, Sun's replacement for single user mode with a very few things running
2 = multi-user mode, a lot of stuff running and people can sign on
3 = makes local resources available to other systems
4 = not used
5 = power down the system
6 = reboot the system

So "init 0" is very different... no OS at all will be running. Level s and Level S are different names for the same thing. Level S and 1 are very close in concept. The difference is that a few things will be running in level 1 and level 1 requires a good /etc/inittab.

Also Sun and everyone else cheat a little bit. If you are in a high level and enter level S, you do not really go all the way down to a "true" level S. They will leave a few things running. This leads the system admin's rule that a "true" level S is achieved only by rebooting and coming up directly to level S. This is partially because of intent and partially because some stuff just will not die.
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