shadow/man/limits.5.xml

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<refentry id='limits.5'>
  <!-- $Id$ -->
  <refentryinfo>
    <author>
      <firstname>Luca</firstname>
      <surname>Berra</surname>
      <contrib>Creation, 1997</contrib>
    </author>
    <author>
      <firstname>Thomas</firstname>
      <surname>Kłoczko</surname>
      <email>kloczek@pld.org.pl</email>
      <contrib>shadow-utils maintainer, 2000 - 2007</contrib>
    </author>
    <author>
      <firstname>Nicolas</firstname>
      <surname>François</surname>
      <email>nicolas.francois@centraliens.net</email>
      <contrib>shadow-utils maintainer, 2007 - now</contrib>
    </author>
  </refentryinfo>
  <refmeta>
    <refentrytitle>limits</refentrytitle>
    <manvolnum>5</manvolnum>
    <refmiscinfo class="sectdesc">File Formats and Configuration Files</refmiscinfo>
    <refmiscinfo class="source">shadow-utils</refmiscinfo>
    <refmiscinfo class="version">&SHADOW_UTILS_VERSION;</refmiscinfo>
  </refmeta>
  <refnamediv id='name'>
    <refname>limits</refname>
    <refpurpose>resource limits definition</refpurpose>
  </refnamediv>
  <!-- body begins here -->

  <refsect1 id='description'>
    <title>DESCRIPTION</title>
    <para>
      The <emphasis remap='I'>limits</emphasis> file 
      (<filename>/etc/limits</filename> by default
      or LIMITS_FILE defined <filename>config.h</filename>) describes 
      the resource limits you wish to impose. It should be owned by 
      root and readable by root account only.
    </para>

    <para>
      By default no quota is imposed on 'root'. In fact, there is no way to
      impose limits via this procedure to root-equiv accounts (accounts with
      UID 0).
    </para>

    <para>Each line describes a limit for a user in the form:</para>

    <para>
      <emphasis remap='I'>user LIMITS_STRING</emphasis>
    </para>

    <para>or in the form:</para>

    <para>
      <emphasis remap='I'>@group LIMITS_STRING</emphasis>
    </para>

    <para>
      The <emphasis>LIMITS_STRING</emphasis> is a string of a concatenated
      list of resource limits. Each limit consists of a letter identifier
      followed by a numerical limit.
    </para>

    <para>The valid identifiers are:</para>

    <itemizedlist>
      <listitem><para>A: max address space (KB)</para></listitem>
      <listitem><para>C: max core file size (KB)</para></listitem>
      <listitem><para>D: max data size (KB)</para></listitem>
      <listitem><para>F: maximum file size (KB)</para></listitem>
      <listitem><para>K: file creation mask, set by
	<citerefentry>
	  <refentrytitle>umask</refentrytitle><manvolnum>2</manvolnum>
	</citerefentry>.</para>
      </listitem>
      <listitem><para>I: max nice value (0..39 which translates to
      20..-19)</para></listitem>
      <listitem><para>L: max number of logins for this user</para></listitem>
      <listitem><para>M: max locked-in-memory address space (KB)</para></listitem>
      <listitem><para>N: max number of open files</para></listitem>
      <listitem><para>O: max real time priority</para></listitem>
      <listitem><para>P: process priority, set by
	<citerefentry>
	  <refentrytitle>setpriority</refentrytitle><manvolnum>2</manvolnum>
	</citerefentry>.</para>
      </listitem>
      <listitem><para>R: max resident set size (KB)</para></listitem>
      <listitem><para>S: max stack size (KB)</para></listitem>
      <listitem><para>T: max CPU time (MIN)</para></listitem>
      <listitem><para>U: max number of processes</para></listitem>
    </itemizedlist>

    <para>
      For example, <emphasis remap='I'>L2D2048N5</emphasis> is a valid
      <emphasis>LIMITS_STRING</emphasis>. For reading convenience, the
      following entries are equivalent:
    </para>

    <programlisting>
      username L2D2048N5
      username L2 D2048 N5
    </programlisting>

    <para>
      Be aware that after <emphasis remap='I'>username</emphasis> the rest
      of the line is considered a limit string, thus comments are not
      allowed. An invalid limits string will be rejected (not considered) by
      the <command>login</command> program.
    </para>

    <para>
      The default entry is denoted by username "<emphasis>*</emphasis>". If
      you have multiple <emphasis remap='I'>default</emphasis> entries in
      your <emphasis>LIMITS_FILE</emphasis>, then the last one will be used
      as the default entry.
    </para>

    <para>
      The limits specified in the form "<replaceable>@group</replaceable>"
      apply to the members of the specified
      <replaceable>group</replaceable>.
    </para>

    <para>
      If more than one line with limits for a user exist, only the first line for
      this user will be considered.
    </para>

    <para>
      If no lines are specified for a user, the last
      <replaceable>@group</replaceable> line matching a group whose the
      user is a member of will be considered, or the last line with
      default limits if no groups contain the user.
    </para>

    <para>
      To completely disable limits for a user, a single dash
      "<emphasis>-</emphasis>" will do.
    </para>

    <para>
      To disable a limit for a user, a single dash
      "<replaceable>-</replaceable>" can be used instead of the numerical
      value for this limit.
    </para>

    <para>
      Also, please note that all limit settings are set PER LOGIN. They are
      not global, nor are they permanent. Perhaps global limits will come,
      but for now this will have to do ;)
    </para>
  </refsect1>

  <refsect1 id='files'>
    <title>FILES</title>
    <variablelist>
      <varlistentry>
	<term><filename>/etc/limits</filename></term>
	<listitem><para></para></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1 id='see_also'>
    <title>SEE ALSO</title>
    <para>
      <citerefentry>
	<refentrytitle>login</refentrytitle><manvolnum>1</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>setpriority</refentrytitle><manvolnum>2</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>setrlimit</refentrytitle><manvolnum>2</manvolnum>
      </citerefentry>.
    </para>
  </refsect1>
</refentry>