what are init 0 init 1 init 2 init 3 init 4 init 5 init 6 init s init S init metc

The best solution to know about these init levels is to understand the " man init " command output on Unix.

There are basically 8 runlevels in unix. I will briefly tell some thing about the different init levels and their use. 
Run Level:  At any given time, the system is in one  of  eight  possible run  levels.  A  run level is a software configuration under which only a selected group of processes  exists.  Processes spawned  by init for each of these run levels are defined in /etc/inittab. init can be in one of eight  run  levels,  0-6 and  S  or  s (S and s are identical). The run level changes when a privileged user runs /sbin/init.

init 0 :  Shutdown (goes thru the /etc/rc0.d/* scripts then halts)
init 1  :  Single user mode or emergency mode means no network no multitasking is present in this mode only root has access in this runlevel
init 2  :  No network but multitasking support is present .
init 3  :  Network is present multitasking is present but with out GUI .
init 4  :  It is similar to runlevel 3; It is reserved for other purposes in research.
init 5  :  Network is present multitasking and GUI is present with sound etc.
init 6  :  This runlevel is defined to system restart.
init s   : Tells the init command to enter the maintenance mode. When the
system enters maintenance mode from another run level, only the system console
is used as the terminal.
init S  : Same as init s.
init m : Same as init s and init S.
init M : Same as init s or init S or init m.

We can take it from above that 4 options(S,s,M,m) are synonymous.

16 comments to "what are init 0 init 1 init 2 init 3 init 4 init 5 init 6 init s init S init metc"

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Whoever writes Inappropriate/Vulgar comments to context, generally want to be anonymous …So I hope U r not the one like that?
For lazy logs, u can at least use Name/URL option which doesn’t even require any sign-in, The good thing is that it can accept your lovely nick name also and the URL is not mandatory too.
Thanks for your patience
~Krishna(I love "Transparency")

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