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+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+ Copyright (c) 2013 Eric W. Biederman
+ All rights reserved.
+
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted provided that the following conditions
+ are met:
+ 1. Redistributions of source code must retain the above copyright
+ notice, this list of conditions and the following disclaimer.
+ 2. Redistributions in binary form must reproduce the above copyright
+ notice, this list of conditions and the following disclaimer in the
+ documentation and/or other materials provided with the distribution.
+ 3. The name of the copyright holders or contributors may not be used to
+ endorse or promote products derived from this software without
+ specific prior written permission.
+
+ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+ PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
+<!-- SHADOW-CONFIG-HERE -->
+]>
+<refentry id='subgid.5'>
+ <refentryinfo>
+ <author>
+ <firstname>Eric</firstname>
+ <surname>Biederman</surname>
+ <contrib>Creation, 2013</contrib>
+ </author>
+ </refentryinfo>
+ <refmeta>
+ <refentrytitle>subgid</refentrytitle>
+ <manvolnum>5</manvolnum>
+ <refmiscinfo class="sectdesc">File Formats and Conversions</refmiscinfo>
+ <refmiscinfo class="source">shadow-utils</refmiscinfo>
+ <refmiscinfo class="version">&SHADOW_UTILS_VERSION;</refmiscinfo>
+ </refmeta>
+ <refnamediv id='name'>
+ <refname>subgid</refname>
+ <refpurpose>the subordinate gid file</refpurpose>
+ </refnamediv>
+
+ <refsect1 id='description'>
+ <title>DESCRIPTION</title>
+ <para>
+ Each line in <filename>/etc/subgid</filename> contains
+ a user name and a range of subordinate group ids that user
+ is allowed to use.
+
+ This is specified with three fields delimited by colons
+ (<quote>:</quote>).
+ These fields are:
+ </para>
+ <itemizedlist mark='bullet'>
+ <listitem>
+ <para>login name or UID</para>
+ </listitem>
+ <listitem>
+ <para>numerical subordinate group ID</para>
+ </listitem>
+ <listitem>
+ <para>numerical subordinate group ID count</para>
+ </listitem>
+ </itemizedlist>
+
+ <para>
+ This file specifies the group IDs that ordinary users can use, with
+ the <command>newgidmap</command> command, to configure gid mapping
+ in a user namespace.
+ </para>
+
+ <para>
+ Multiple ranges may be specified per user.
+ </para>
+
+ <para>
+ When large number of entries (10000-100000 or more) are defined in
+ <filename>/etc/subgid</filename>, parsing performance penalty will
+ become noticeable. In this case it is recommended to use UIDs
+ instead of login names. Benchmarks have shown speed-ups up to 20x.
+ </para>
+
+ </refsect1>
+
+ <refsect1 id='files'>
+ <title>FILES</title>
+ <variablelist>
+ <varlistentry>
+ <term><filename>/etc/subgid</filename></term>
+ <listitem>
+ <para>Per user subordinate group IDs.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>/etc/subgid-</filename></term>
+ <listitem>
+ <para>Backup file for /etc/subgid.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+
+ <refsect1 id='see_also'>
+ <title>SEE ALSO</title>
+ <para>
+ <citerefentry>
+ <refentrytitle>login.defs</refentrytitle><manvolnum>5</manvolnum>
+ </citerefentry>,
+ <citerefentry>
+ <refentrytitle>newgidmap</refentrytitle><manvolnum>1</manvolnum>
+ </citerefentry>,
+ <citerefentry>
+ <refentrytitle>newuidmap</refentrytitle><manvolnum>1</manvolnum>
+ </citerefentry>,
+ <citerefentry>
+ <refentrytitle>newusers</refentrytitle><manvolnum>8</manvolnum>
+ </citerefentry>,
+ <citerefentry>
+ <refentrytitle>subuid</refentrytitle><manvolnum>5</manvolnum>
+ </citerefentry>,
+ <citerefentry>
+ <refentrytitle>useradd</refentrytitle><manvolnum>8</manvolnum>
+ </citerefentry>,
+ <citerefentry>
+ <refentrytitle>userdel</refentrytitle><manvolnum>8</manvolnum>
+ </citerefentry>,
+ <citerefentry>
+ <refentrytitle>usermod</refentrytitle><manvolnum>8</manvolnum>
+ </citerefentry>,
+ <citerefentry>
+ <refentrytitle>user_namespaces</refentrytitle><manvolnum>7</manvolnum>
+ </citerefentry>.
+ </para>
+ </refsect1>
+</refentry>