mirror of https://github.com/tLDP/LDP
239 lines
7.8 KiB
XML
239 lines
7.8 KiB
XML
<chapter id="oper">
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<title>Basic operation</title>
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<abstract>
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<para>This chapter describes basic operations done during everyday
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system administrator work. This operations are not much different
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then in other Linux based systems hence we concentrate on the
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specific for PLD ones.</para>
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</abstract>
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<section id="restart-shutdown">
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<title>Restarting and shutting down</title>
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<para>
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Traditional way of shutting down the machine is via <command>shutdown</command>
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command, e.g.:
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<programlisting>shutdown -h now</programlisting></para>
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<para>
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But two simple commands can be used instead:
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<itemizedlist>
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<listitem>
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<para><command>halt</command> immediately runs shutdown procedure</para>
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</listitem>
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<listitem>
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<para><command>reboot</command> immediately runs reboot procedure</para>
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</listitem>
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</itemizedlist>
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On PC computers reboot can be also invoked by pressing Ctrl-Alt-Del sequence.
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</para>
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</section>
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<section id="subsystems">
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<title>Starting/stopping particular subsystems</title>
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<para>
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In every system there is a number of special tasks that needs
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to be performed (in proper order) at startup and shutdown.
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This usually involves setup (e.g. network setup, sound setup),
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as well as launching some services (e.g. http server, ssh server).
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The tasks that needs to be handled in that way are commonly referred to as
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subsystems or services.
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</para>
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<para>
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Running of particular subsystems/services can be easily
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controlled with system scripts. Each vital subsystem/service has its
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driver script
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available in <filename>/etc/rc.d/init.d/</filename> directory.
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If you run script without parameters, it displays short info, e.g.
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<emphasis>network</emphasis> subsystem script displays:
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<programlisting>
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# /etc/rc.d/init.d/network
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Usage: /etc/rc.d/init.d/network {start|stop|restart|status}
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</programlisting>
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Most scripts support <emphasis>start</emphasis>,
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<emphasis>stop</emphasis>, <emphasis>restart</emphasis>,
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and <emphasis>status</emphasis> argument:
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<variablelist>
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<varlistentry>
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<term>start</term>
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<listitem>
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<para>runs the subsystem/service</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>stop</term>
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<listitem>
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<para>stops the subsystem/service</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>restart</term>
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<listitem>
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<para>restarts the subsystem/service</para>
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<note>
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<para>
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Usually this is equivalent to <emphasis>start</emphasis>
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and <emphasis>stop</emphasis>, but in some cases
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it can be different.
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</para>
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</note>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>status</term>
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<listitem>
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<para>shows the status of the subsystem/service</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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<example>
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<title>Starting/stopping services</title>
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<para>
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This example sequence stops and starts network again
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(turning on/off existing interfaces, setting default routing, etc. See
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<xref linkend="network"/>)
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</para>
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<programlisting>
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[root@pldmachine root]# /etc/rc.d/init.d/network stop
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Shutting down interface eth0.......................................[ DONE ]
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Shutting down interface eth1.......................................[ DONE ]
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[root@pldmachine root]# /etc/rc.d/init.d/network start
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Setting network parameters.........................................[ DONE ]
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Bringing up interface eth0.........................................[ DONE ]
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Bringing up interface eth1.........................................[ DONE ]
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</programlisting>
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</example>
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<para>
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Every subsystem script contains information in what runlevels
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that subsystem should be started by default with line like this
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(example line from <filename>/etc/rc.d/init.d/syslog</filename> subsystem):
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<programlisting># chkconfig: 2345 30 70></programlisting>
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This tells rc-scripts to run the subsystem when entering runlevels
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2, 3, 4, 5 (and respectively, to stop subsystem when leaving one of these
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runlevels). Numbers 30 and 70 are priority levels for start/stop.
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See <citerefentry>
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<refentrytitle>chkconfig</refentrytitle>
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<manvolnum>8</manvolnum>
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</citerefentry> for details.
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</para>
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<para>
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Set of subsystems/services run in particular runlevel can be changed
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with <command>chkconfig</command> command.
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Some examples:
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<programlisting>
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] # list current status
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] # asterisks (***) means the service/subsys is started/stopped in runlevel
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]
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] chkconfig --list
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gpm 0:--- 1:--- 2:*** 3:*** 4:*** 5:*** 6:---
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network 0:--- 1:--- 2:*** 3:*** 4:*** 5:*** 6:---
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httpd 0:--- 1:--- 2:--- 3:*** 4:*** 5:*** 6:---
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random 0:--- 1:*** 2:*** 3:*** 4:*** 5:*** 6:---
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qmail 0:--- 1:--- 2:*** 3:*** 4:*** 5:*** 6:---
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single 0:--- 1:*** 2:--- 3:--- 4:--- 5:--- 6:---
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klogd 0:--- 1:--- 2:*** 3:*** 4:*** 5:*** 6:---
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console 0:--- 1:--- 2:--- 3:*** 4:*** 5:*** 6:---
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sshd 0:--- 1:--- 2:--- 3:*** 4:*** 5:*** 6:---
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nfsfs 0:--- 1:--- 2:--- 3:*** 4:*** 5:*** 6:---
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timezone 0:--- 1:--- 2:*** 3:*** 4:*** 5:*** 6:---
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syslog 0:--- 1:--- 2:*** 3:*** 4:*** 5:*** 6:---
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rc-inetd 0:--- 1:--- 2:--- 3:*** 4:*** 5:*** 6:---
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] # exclude sshd service from runlevels 345
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] chkconfig sshd off
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] # include sshd service in runlevels 345 again
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] chkconfig sshd on
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</programlisting>
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<note>
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<para>
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Removing/adding service to runlevel takes effect next time the
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runlevel is changed.
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It does not automatically start subsystem if one is not running,
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or stop it if it's already running.
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</para>
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</note>
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</para>
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</section>
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<section id="runlevels">
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<title>Changing runlevels</title>
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<para>
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PLD system can be run in several <emphasis>runlevels</emphasis>:
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</para>
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<variablelist>
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<varlistentry>
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<term>Runlevel 1</term>
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<listitem>
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<para>
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Single user mode. Used by administrator for rescue/emergency/system
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maintenance reasons.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Runlevel 2</term>
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<listitem>
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<para>
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Multiuser level, but without Network File System
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Runlevel 3</term>
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<listitem>
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<para>
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Normal multiuser level. This is most commonly used runlevel.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Runlevel 5</term>
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<listitem>
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<para>
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Normal multiuser level with X Window environment started by default.
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This is popular choice for workstations.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>
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There are two more runlevels: these are Runlevel 0 and Runlevel 6.
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First one is used to bring all subsystems/processes down before system halt,
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second is used to accomplish similar task before system reboot.
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</para>
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<para>
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System boots up in <emphasis>default runlevel</emphasis> that is
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defined in <filename>/etc/inittab</filename> (see <xref linkend="inittab"/>)
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which is usually 3 or 5.
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Current runlevel can be changed with <command>telinit</command> command.
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For example, if system is running level 3, issuing <command>telinit 2</command>
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brings it to level 2 (as a consequence, NFS subsystems will be stopped).
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</para>
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</section>
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&managing;
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</chapter>
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