System States

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.

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