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systemd/man/sysusers.d.xml
Zbigniew Jędrzejewski-Szmek fc706b4816 man: fix quickhelp listing in sysusers.d(5) 
Fixes #16958.
2020-09-08 17:30:42 +02:00

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<?xml version="1.0"?>
<!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<refentry id="sysusers.d" conditional='ENABLE_SYSUSERS'
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sysusers.d</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sysusers.d</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>sysusers.d</refname>
<refpurpose>Declarative allocation of system users and groups</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>/etc/sysusers.d/*.conf</filename></para>
<para><filename>/run/sysusers.d/*.conf</filename></para>
<para><filename>/usr/lib/sysusers.d/*.conf</filename></para>
<programlisting>
#Type Name ID GECOS Home directory Shell
u user_name uid "User Description" /home/dir /path/to/shell
u user_name uid:gid "User Description" /home/dir /path/to/shell
u user_name /file/owned/by/user "User Description" /home/dir /path/to/shell
g group_name gid
g group_name /file/owned/by/group
m user_name group_name
r - lowest-highest</programlisting>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><command>systemd-sysusers</command> uses the files from
<filename>sysusers.d</filename> directory to create system users and groups and
to add users to groups, at package installation or boot time. This tool may be
used to allocate system users and groups only, it is not useful for creating
non-system (i.e. regular, "human") users and groups, as it accesses
<filename>/etc/passwd</filename> and <filename>/etc/group</filename> directly,
bypassing any more complex user databases, for example any database involving NIS
or LDAP.</para>
</refsect1>
<refsect1>
<title>Configuration Directories and Precedence</title>
<para>Each configuration file shall be named in the style of
<filename><replaceable>package</replaceable>.conf</filename> or
<filename><replaceable>package</replaceable>-<replaceable>part</replaceable>.conf</filename>.
The second variant should be used when it is desirable to make it
easy to override just this part of configuration.</para>
<para>Files in <filename>/etc/sysusers.d</filename> override files
with the same name in <filename>/usr/lib/sysusers.d</filename> and
<filename>/run/sysusers.d</filename>. Files in
<filename>/run/sysusers.d</filename> override files with the same
name in <filename>/usr/lib/sysusers.d</filename>. Packages should
install their configuration files in
<filename>/usr/lib/sysusers.d</filename>. Files in
<filename>/etc/sysusers.d</filename> are reserved for the local
administrator, who may use this logic to override the
configuration files installed by vendor packages. All
configuration files are sorted by their filename in lexicographic
order, regardless of which of the directories they reside in. If
multiple files specify the same path, the entry in the file with
the lexicographically earliest name will be applied. All later
entries for the same user and group names will be logged as warnings.
</para>
<para>If the administrator wants to disable a configuration file
supplied by the vendor, the recommended way is to place a symlink
to <filename>/dev/null</filename> in
<filename>/etc/sysusers.d/</filename> bearing the same filename.
</para>
</refsect1>
<refsect1>
<title>Configuration File Format</title>
<para>The file format is one line per user or group containing name, ID, GECOS
field description, home directory, and login shell:</para>
<programlisting>#Type Name ID GECOS Home directory Shell
u httpd 404 "HTTP User"
u _authd /usr/bin/authd "Authorization user"
u postgres - "Postgresql Database" /var/lib/pgsql /usr/libexec/postgresdb
g input - -
m _authd input
u root 0 "Superuser" /root /bin/zsh
r - 500-900
</programlisting>
<para>Empty lines and lines beginning with the <literal>#</literal> character are ignored, and may be used for
commenting.</para>
<refsect2>
<title>Type</title>
<para>The type consists of a single letter. The following line
types are understood:</para>
<variablelist>
<varlistentry>
<term><varname>u</varname></term>
<listitem><para>Create a system user and group of the specified name should
they not exist yet. The user's primary group will be set to the group
bearing the same name unless the ID field specifies it. The account will be
created disabled, so that logins are not allowed.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>g</varname></term>
<listitem><para>Create a system group of the specified name
should it not exist yet. Note that <varname>u</varname>
implicitly creates a matching group. The group will be
created with no password set.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>m</varname></term>
<listitem><para>Add a user to a group. If the user or group
do not exist yet, they will be implicitly
created.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>r</varname></term>
<listitem><para>Add a range of numeric UIDs/GIDs to the pool
to allocate new UIDs and GIDs from. If no line of this type
is specified, the range of UIDs/GIDs is set to some
compiled-in default. Note that both UIDs and GIDs are
allocated from the same pool, in order to ensure that users
and groups of the same name are likely to carry the same
numeric UID and GID.</para></listitem>
</varlistentry>
</variablelist>
</refsect2>
<refsect2>
<title>Name</title>
<para>The name field specifies the user or group name. The specified name must consist only of the characters a-z,
A-Z, 0-9, <literal>_</literal> and <literal>-</literal>, except for the first character which must be one of a-z,
A-Z or <literal>_</literal> (i.e. numbers and <literal>-</literal> are not permitted as first character). The
user/group name must have at least one character, and at most 31.</para>
<para>For further details about the syntax of user/group names, see <ulink
url="https://systemd.io/USER_NAMES">User/Group Name Syntax</ulink>.</para>
<para>It is strongly recommended to pick user and group names that are unlikely to clash with normal users
created by the administrator. A good scheme to guarantee this is by prefixing all system and group names with the
underscore, and avoiding too generic names.</para>
<para>For <varname>m</varname> lines, this field should contain
the user name to add to a group.</para>
<para>For lines of type <varname>r</varname>, this field should
be set to <literal>-</literal>.</para>
</refsect2>
<refsect2>
<title>ID</title>
<para>For <varname>u</varname> and <varname>g</varname>, the
numeric 32-bit UID or GID of the user/group. Do not use IDs 65535
or 4294967295, as they have special placeholder meanings.
Specify <literal>-</literal> for automatic UID/GID allocation
for the user or group (this is strongly recommended unless it is strictly
necessary to use a specific UID or GID). Alternatively, specify an absolute path
in the file system. In this case, the UID/GID is read from the
path's owner/group. This is useful to create users whose UID/GID
match the owners of pre-existing files (such as SUID or SGID
binaries).
The syntaxes <literal><replaceable>uid</replaceable>:<replaceable>gid</replaceable></literal> and
<literal><replaceable>uid</replaceable>:<replaceable>groupname</replaceable></literal> are supported to
allow creating users with specific primary groups. The given group must be created explicitly, or it
must already exist. Specifying <literal>-</literal> for the UID in these syntaxes is also supported.
</para>
<para>For <varname>m</varname> lines, this field should contain
the group name to add to a user to.</para>
<para>For lines of type <varname>r</varname>, this field should
be set to a UID/GID range in the format
<literal>FROM-TO</literal>, where both values are formatted as
decimal ASCII numbers. Alternatively, a single UID/GID may be
specified formatted as decimal ASCII numbers.</para>
</refsect2>
<refsect2>
<title>GECOS</title>
<para>A short, descriptive string for users to be created, enclosed in
quotation marks. Note that this field may not contain colons.</para>
<para>Only applies to lines of type <varname>u</varname> and should otherwise
be left unset (or <literal>-</literal>).</para>
</refsect2>
<refsect2>
<title>Home Directory</title>
<para>The home directory for a new system user. If omitted, defaults to the
root directory.</para>
<para>Only applies to lines of type <varname>u</varname> and should otherwise
be left unset (or <literal>-</literal>). It is recommended to omit this, unless
software strictly requires a home directory to be set.</para>
</refsect2>
<refsect2>
<title>Shell</title>
<para>The login shell of the user. If not specified, this will be set to
<filename>/usr/sbin/nologin</filename>, except if the UID of the user is 0, in
which case <filename>/bin/sh</filename> will be used.</para>
<para>Only applies to lines of type <varname>u</varname> and should otherwise
be left unset (or <literal>-</literal>). It is recommended to omit this, unless
a shell different <filename>/usr/sbin/nologin</filename> must be used.</para>
</refsect2>
</refsect1>
<refsect1>
<title>Specifiers</title>
<para>Specifiers can be used in the <literal>Name</literal>, <literal>ID</literal>,
<literal>GECOS</literal>, <literal>Home directory</literal>, and <literal>Shell</literal> fields. An
unknown or unresolvable specifier is treated as invalid configuration. The following expansions are
understood:</para>
<table class='specifiers'>
<title>Specifiers available</title>
<tgroup cols='3' align='left' colsep='1' rowsep='1'>
<colspec colname="spec" />
<colspec colname="mean" />
<colspec colname="detail" />
<thead>
<row>
<entry>Specifier</entry>
<entry>Meaning</entry>
<entry>Details</entry>
</row>
</thead>
<tbody>
<xi:include href="standard-specifiers.xml" xpointer="a"/>
<xi:include href="standard-specifiers.xml" xpointer="b"/>
<xi:include href="standard-specifiers.xml" xpointer="B"/>
<xi:include href="standard-specifiers.xml" xpointer="H"/>
<xi:include href="standard-specifiers.xml" xpointer="l"/>
<xi:include href="standard-specifiers.xml" xpointer="m"/>
<xi:include href="standard-specifiers.xml" xpointer="o"/>
<row>
<entry><literal>%T</literal></entry>
<entry>Directory for temporary files</entry>
<entry>This is either <filename>/tmp</filename> or the path <literal>$TMPDIR</literal>, <literal>$TEMP</literal> or <literal>$TMP</literal> are set to.</entry>
</row>
<xi:include href="standard-specifiers.xml" xpointer="v"/>
<row>
<entry><literal>%V</literal></entry>
<entry>Directory for larger and persistent temporary files</entry>
<entry>This is either <filename>/var/tmp</filename> or the path <literal>$TMPDIR</literal>, <literal>$TEMP</literal> or <literal>$TMP</literal> are set to.</entry>
</row>
<xi:include href="standard-specifiers.xml" xpointer="w"/>
<xi:include href="standard-specifiers.xml" xpointer="W"/>
<xi:include href="standard-specifiers.xml" xpointer="percent"/>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1>
<title>Idempotence</title>
<para>Note that <command>systemd-sysusers</command> will do nothing if the
specified users or groups already exist or the users are members of specified
groups, so normally there is no reason to override
<filename>sysusers.d</filename> vendor configuration, except to block certain
users or groups from being created.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-sysusers</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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