[aclug-L] FW: System States

["Dale W Hodge" <dwh@xxxxxxxxxxxxxxxx>]

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From: Linux_Tips_and_Tricks@xxxxxxxxxxxxxxx
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Sent: Friday, January 25, 2002 12:30 AM


LINUX TIPS AND TRICKS --- January 25, 2002
Published by ITworld.com -- changing the way you view IT
http://www.itworld.com/newsletters
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HIGHLIGHTS

* This week, Danny explains the meaning of system states and shows you
  how to switch from one state to another.

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System States
By Danny Kalev

Systems States and their Meanings
A Linux system may run in one of seven possible states numbered from 0
to 6, as well as the single-user state that the letters s or S
represent. Here is a description of all these states:

    * State 0 is the halt state. When you switch a system to state 0,
      it will shutdown immediately.
    * State 1, known as the administrative state, allows access only to
      a super-user. Using this state, a system administrator can
      perform various maintenance operations and installations without
      interference from other users.
    * State 2 is the partial multiple user state. It allows multiple
      users to login but it disables remote file sharing.
    * State 3 is the multiple user state. It allows multiple users to
      login and enables remote file sharing. This is the default state
      for the command line interface.
    * State 4 is unused.
    * State 5 is the default state for graphical logins that use
      display managers such as gdm and xdm. If you choose to use
      graphical logins during the installation process, this will be
      your default state instead of state 3, which would be the default
      otherwise.
    * State 6 shuts down the system and reboots (note that state 0
      shuts down the system without performing an automatic reboot
      afterwards).
    * State s or S is the single-user state. It restricts the number of
      logged in users to one.

Detecting and Setting the System's State
To detect the state in which your system is currently running, use the
runlevel command (the term 'runlevel' is a synonym for 'state'). For
example:

     #runlevel
      N 3

On startup, Linux enters the default state. The system's default state
is stored in a file called /etc/inittab. You may override it by
changing the value of the init default entry. To change the current
system state, use the init command. For example, to switch to a single-
user mode, type the following command:

     #init s

Likewise, to shut the system down immediately, use the following
command:

    #init 0

Note, however, that, in general, you should use the 'shutdown' command.
It allows you to include a warning message that is sent to all the
users that are currently logged in or specify a delay.

About the author(s)
-------------------
Danny Kalev is a system analyst and software engineer with more than 10
years of experience, specializing in C++ and object-oriented analysis
and design on various platforms including VMS, DOS, Windows, Unix, and
Linux. His technical interests involve code optimization, networking,
and distributed computing. He is also a member of the ANSI C++
standardization committee and the author of ANSI/ISO C++ Professional
Programmer's Handbook (Que, 1999). Danny can be reached at
linuxnl@xxxxxxxxxx.
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ADDITIONAL RESOURCES

About system states
http://itw.itworld.com/GoNow/a14724a51177a76028222a3

Run levels revisited
http://itw.itworld.com/GoNow/a14724a51177a76028222a0

In the Beginning
http://itw.itworld.com/GoNow/a14724a51177a76028222a4

An Introduction to the Linux Operating System Architecture
http://itw.itworld.com/GoNow/a14724a51177a76028222a2

Linux Init run levels, and startup configuration
http://itw.itworld.com/GoNow/a14724a51177a76028222a1
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ITWORLD.COM NEWSLETTER ARCHIVE

Index of Linux Tips and Tricks
http://www.itworld.com/nl/lnx_tip/

The dl Library
http://www.itworld.com/nl/lnx_tip/05112001/

Memory Locking
http://www.itworld.com/nl/lnx_tip/05182001/
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