Runlevel
 

Dear All
Pls tell why different run levels are required.


Prasanta

They are used to make the system run in different levels of operation. You're best bet is some background reading really - http://en.wikipedia.org/wiki/Runlevel

Rats...
 

And here I was going to answer:
NO. That information is secret!


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Some runlevels are specific to system shutdown or special states, but the available ones can specify a different set of programs, processes, or services to run. Boot to runlevel 2 and you have a web server and router sans desktop, runlevel 3 you have an XWindows desktop with XFCE and media players in your menu, runlevel 5 and you find yourself running GNOME with OpenOffice and business applications in your menus: all without multi-os boot, virtualization, or jumping through hoops -- just the magic of Unix style runlevels!

And some people want to retire that system. Are they Crazy? [NOTE: rhetorical question, not to be answered rudely please. ;) ]
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And after all that: What made you think that they are all "required"?
Your reading (See post by Acid*) will teach you which are required under system that use runlevels.