shadow/man/subuid.5.xml
Bostjan Skufca 37e2a687e3 sub[ug]id manpages: add note about performance when using login names versus UIDs
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
2014-09-17 15:48:17 -05:00

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<?xml version="1.0" encoding="UTF-8"?>
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<!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='subuid.5'>
<refmeta>
<refentrytitle>subuid</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>subuid</refname>
<refpurpose>the subordinate uid file</refpurpose>
</refnamediv>
<refsect1 id='description'>
<title>DESCRIPTION</title>
<para>
Each line in <filename>/etc/subuid</filename> contains
a user name and a range of subordinate user 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 user ID</para>
</listitem>
<listitem>
<para>numerical subordinate user ID count</para>
</listitem>
</itemizedlist>
<para>
This file specifies the user IDs that ordinary users can use, with
the <command>newuidmap</command> command, to configure uid 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/subuid</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/subuid</filename></term>
<listitem>
<para>Per user subordinate user IDs.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><filename>/etc/subuid-</filename></term>
<listitem>
<para>Backup file for /etc/subuid.</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>1</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>subgid</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>