[aclug-L] FW: System States
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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
* This week, Danny explains the meaning of system states and shows you
how to switch from one state to another.
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
* State 6 shuts down the system and reboots (note that state 0
shuts down the system without performing an automatic reboot
* 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
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:
Likewise, to shut the system down immediately, use the following
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
About system states
Run levels revisited
In the Beginning
An Introduction to the Linux Operating System Architecture
Linux Init run levels, and startup configuration
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