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run levels
Authored by: forero on Feb 11, '02 09:13:41AM

Most UNIX-like systems utilize the concept of run levels. In my department we use run-level 3 as fully up and 0 as single user mode. In fact, run level 0 is universally single user mode. It's the other levels that change from system to system. There is nothing harmful in putting your system in run level 0.

What can cause damage is 'halting' your system. There is a good chance of file corruption if you halt your system. There are procedures for halting that will help prevent file corruption, but then why not just shutdown properly.

On most UNIX-like systems inittab manages the run levels, telling the system what to run at different run levels. Mac OS X seems to have two run levels and these are controlled by the rc.* files in /etc.
In short, if you want to restart but don’t want it to adversely affect your ‘up-time’, then going to run level 0 is a good option. Almost everything will be shutdown and restarted when you exit back into run level 1.



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run levels
Authored by: Anonymous on Feb 11, '02 12:49:47PM

Runlevels are a System V (Sys V, Linux, Solaris, SCO, etc) feature. BSD does not utilize this concept of runlevels.

A little background if you didn't know, there are basically two main lineages of UNIX: System V and BSD. There are actually several major differences between each style.



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run levels
Authored by: WillyT on Feb 12, '02 11:32:14AM
Found this in the FreeBSD Handbook p.148 quote 7.5.2 Single-User Mode ... It can Also be reached by calling shutdown without the reboot (-r) or halt (-h) options, from multi-user mode. ... 7.5.3 Multi-User Mode If init finds your filesystems to be in order, or once the user has finished in single-user mode, the system enters multi-user mode, in which it starts the resource configuration of the system. endquote There are also boot levels but these are NOT the same thing. There are hundreds of pages to this manual. The manual is available from The FreeBSD Project

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