Allow braceless variables to be expanded

[thirdparty/systemd.git] / man / os-release.xml

<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<!--
  This file is part of systemd.

  Copyright 2010 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->

<refentry id="os-release">
  <refentryinfo>
    <title>os-release</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Lennart</firstname>
        <surname>Poettering</surname>
        <email>lennart@poettering.net</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>os-release</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>os-release</refname>
    <refpurpose>Operating system identification</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>/etc/os-release</filename></para>
    <para><filename>/usr/lib/os-release</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>The <filename>/etc/os-release</filename> and
    <filename>/usr/lib/os-release</filename> files contain operating
    system identification data.</para>

    <para>The basic file format of <filename>os-release</filename> is
    a newline-separated list of environment-like shell-compatible
    variable assignments. It is possible to source the configuration
    from shell scripts, however, beyond mere variable assignments, no
    shell features are supported (this means variable expansion is
    explicitly not supported), allowing applications to read the file
    without implementing a shell compatible execution engine. Variable
    assignment values must be enclosed in double or single quotes if
    they include spaces, semicolons or other special characters
    outside of A–Z, a–z, 0–9. Shell special characters ("$", quotes,
    backslash, backtick) must be escaped with backslashes, following
    shell style. All strings should be in UTF-8 format, and
    non-printable characters should not be used. It is not supported
    to concatenate multiple individually quoted strings. Lines
    beginning with "#" shall be ignored as comments.</para>

    <para>The file <filename>/etc/os-release</filename> takes
    precedence over <filename>/usr/lib/os-release</filename>.
    Applications should check for the former, and exclusively use its
    data if it exists, and only fall back to
    <filename>/usr/lib/os-release</filename> if it is missing.
    Applications should not read data from both files at the same
    time. <filename>/usr/lib/os-release</filename> is the recommended
    place to store OS release information as part of vendor trees.
    <filename>/etc/os-release</filename> should be a relative symlink
    to <filename>/usr/lib/os-release</filename>, to provide
    compatibility with applications only looking at
    <filename>/etc</filename>. A relative symlink instead of an
    absolute symlink is necessary to avoid breaking the link in a
    chroot or initrd environment such as dracut.</para>

    <para><filename>os-release</filename> contains data that is
    defined by the operating system vendor and should generally not be
    changed by the administrator.</para>

    <para>As this file only encodes names and identifiers it should
    not be localized.</para>

    <para>The <filename>/etc/os-release</filename> and
    <filename>/usr/lib/os-release</filename> files might be symlinks
    to other files, but it is important that the file is available
    from earliest boot on, and hence must be located on the root file
    system.</para>

    <para>For a longer rationale for <filename>os-release</filename>
    please refer to the <ulink
    url="http://0pointer.de/blog/projects/os-release">Announcement of <filename>/etc/os-release</filename></ulink>.</para>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>The following OS identifications parameters may be set using
    <filename>os-release</filename>:</para>

    <variablelist>

      <varlistentry>
        <term><varname>NAME=</varname></term>

        <listitem><para>A string identifying the operating system,
        without a version component, and suitable for presentation to
        the user. If not set, defaults to
        <literal>NAME=Linux</literal>. Example:
        <literal>NAME=Fedora</literal> or <literal>NAME="Debian
        GNU/Linux"</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>VERSION=</varname></term>

        <listitem><para>A string identifying the operating system
        version, excluding any OS name information, possibly including
        a release code name, and suitable for presentation to the
        user. This field is optional. Example:
        <literal>VERSION=17</literal> or <literal>VERSION="17 (Beefy
        Miracle)"</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ID=</varname></term>

        <listitem><para>A lower-case string (no spaces or other
        characters outside of 0–9, a–z, ".", "_" and "-") identifying
        the operating system, excluding any version information and
        suitable for processing by scripts or usage in generated
        filenames. If not set, defaults to
        <literal>ID=linux</literal>. Example:
        <literal>ID=fedora</literal> or
        <literal>ID=debian</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ID_LIKE=</varname></term>

        <listitem><para>A space-separated list of operating system
        identifiers in the same syntax as the <varname>ID=</varname>
        setting. It should list identifiers of operating systems that
        are closely related to the local operating system in regards
        to packaging and programming interfaces, for example listing
        one or more OS identifiers the local OS is a derivative from.
        An OS should generally only list other OS identifiers it
        itself is a derivative of, and not any OSes that are derived
        from it, though symmetric relationships are possible. Build
        scripts and similar should check this variable if they need to
        identify the local operating system and the value of
        <varname>ID=</varname> is not recognized. Operating systems
        should be listed in order of how closely the local operating
        system relates to the listed ones, starting with the closest.
        This field is optional. Example: for an operating system with
        <literal>ID=centos</literal>, an assignment of
        <literal>ID_LIKE="rhel fedora"</literal> would be appropriate.
        For an operating system with <literal>ID=ubuntu</literal>, an
        assignment of <literal>ID_LIKE=debian</literal> is
        appropriate.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>VERSION_CODENAME=</varname></term>

        <listitem><para>
        A lower-case string (no spaces or other characters outside of
        0–9, a–z, ".", "_" and "-") identifying the operating system
        release code name, excluding any OS name information or
        release version, and suitable for processing by scripts or
        usage in generated filenames. This field is optional and may
        not be implemented on all systems.
        Examples:
        <literal>VERSION_CODENAME=buster</literal>,
        <literal>VERSION_CODENAME=xenial</literal>
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>VERSION_ID=</varname></term>

        <listitem><para>A lower-case string (mostly numeric, no spaces
        or other characters outside of 0–9, a–z, ".", "_" and "-")
        identifying the operating system version, excluding any OS
        name information or release code name, and suitable for
        processing by scripts or usage in generated filenames. This
        field is optional. Example: <literal>VERSION_ID=17</literal>
        or <literal>VERSION_ID=11.04</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>PRETTY_NAME=</varname></term>

        <listitem><para>A pretty operating system name in a format
        suitable for presentation to the user. May or may not contain
        a release code name or OS version of some kind, as suitable.
        If not set, defaults to
        <literal>PRETTY_NAME="Linux"</literal>. Example:
        <literal>PRETTY_NAME="Fedora 17 (Beefy
        Miracle)"</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ANSI_COLOR=</varname></term>

        <listitem><para>A suggested presentation color when showing
        the OS name on the console. This should be specified as string
        suitable for inclusion in the ESC [ m ANSI/ECMA-48 escape code
        for setting graphical rendition. This field is optional.
        Example: <literal>ANSI_COLOR="0;31"</literal> for red, or
        <literal>ANSI_COLOR="1;34"</literal> for light
        blue.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>CPE_NAME=</varname></term>

        <listitem><para>A CPE name for the operating system, in URI
        binding syntax, following the
        <ulink url="http://scap.nist.gov/specifications/cpe/">Common
        Platform Enumeration Specification</ulink> as proposed by the
        NIST. This field is optional. Example:
        <literal>CPE_NAME="cpe:/o:fedoraproject:fedora:17"</literal>
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>HOME_URL=</varname></term>
        <term><varname>SUPPORT_URL=</varname></term>
        <term><varname>BUG_REPORT_URL=</varname></term>
        <term><varname>PRIVACY_POLICY_URL=</varname></term>

        <listitem><para>Links to resources on the Internet related the
        operating system. <varname>HOME_URL=</varname> should refer to
        the homepage of the operating system, or alternatively some
        homepage of the specific version of the operating system.
        <varname>SUPPORT_URL=</varname> should refer to the main
        support page for the operating system, if there is any. This
        is primarily intended for operating systems which vendors
        provide support for. <varname>BUG_REPORT_URL=</varname> should
        refer to the main bug reporting page for the operating system,
        if there is any. This is primarily intended for operating
        systems that rely on community QA.
        <varname>PRIVACY_POLICY_URL=</varname> should refer to the
        main privacy policy page for the operation system, if there is
        any. These settings are optional, and providing only some of
        these settings is common. These URLs are intended to be
        exposed in "About this system" UIs behind links with captions
        such as "About this Operating System", "Obtain Support",
        "Report a Bug", or "Privacy Policy". The values should be in
        <ulink url="https://tools.ietf.org/html/rfc3986">RFC3986
        format</ulink>, and should be <literal>http:</literal> or
        <literal>https:</literal> URLs, and possibly
        <literal>mailto:</literal> or <literal>tel:</literal>. Only
        one URL shall be listed in each setting. If multiple resources
        need to be referenced, it is recommended to provide an online
        landing page linking all available resources. Examples:
        <literal>HOME_URL="https://fedoraproject.org/"</literal> and
        <literal>BUG_REPORT_URL="https://bugzilla.redhat.com/"</literal></para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>BUILD_ID=</varname></term>

        <listitem><para>A string uniquely identifying the system image
        used as the origin for a distribution (it is not updated with
        system updates). The field can be identical between different
        VERSION_IDs as BUILD_ID is an only a unique identifier to a
        specific version. Distributions that release each update as a
        new version would only need to use VERSION_ID as each build is
        already distinct based on the VERSION_ID. This field is
        optional. Example: <literal>BUILD_ID="2013-03-20.3"</literal>
        or <literal>BUILD_ID=201303203</literal>.

        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>VARIANT=</varname></term>

        <listitem><para>
        A string identifying a specific variant or edition of the
        operating system suitable for presentation to the user. This
        field may be used to inform the user that the configuration of
        this system is subject to a specific divergent set of rules or
        default configuration settings. This field is optional and may
        not be implemented on all systems.
        Examples:
        <literal>VARIANT="Server Edition"</literal>,
        <literal>VARIANT="Smart Refrigerator Edition"</literal>
        Note: this field is for display purposes only. The
        <varname>VARIANT_ID</varname> field should be used for making
        programmatic decisions.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>VARIANT_ID=</varname></term>

        <listitem><para>
        A lower-case string (no spaces or other characters outside of
        0–9, a–z, ".", "_" and "-"), identifying a specific variant or
        edition of the operating system. This may be interpreted by
        other packages in order to determine a divergent default
        configuration. This field is optional and may not be
        implemented on all systems.
        Examples:
        <literal>VARIANT_ID=server</literal>,
        <literal>VARIANT_ID=embedded</literal>
        </para></listitem>
      </varlistentry>

    </variablelist>

    <para>If you are reading this file from C code or a shell script
    to determine the OS or a specific version of it, use the
    <varname>ID</varname> and <varname>VERSION_ID</varname> fields,
    possibly with <varname>ID_LIKE</varname> as fallback for
    <varname>ID</varname>. When looking for an OS identification
    string for presentation to the user use the
    <varname>PRETTY_NAME</varname> field.</para>

    <para>Note that operating system vendors may choose not to provide
    version information, for example to accommodate for rolling
    releases. In this case, <varname>VERSION</varname> and
    <varname>VERSION_ID</varname> may be unset. Applications should
    not rely on these fields to be set.</para>

    <para>Operating system vendors may extend the file
    format and introduce new fields. It is highly
    recommended to prefix new fields with an OS specific
    name in order to avoid name clashes. Applications
    reading this file must ignore unknown fields. Example:
    <literal>DEBIAN_BTS="debbugs://bugs.debian.org/"</literal></para>
  </refsect1>

  <refsect1>
    <title>Example</title>

    <programlisting>NAME=Fedora
VERSION="17 (Beefy Miracle)"
ID=fedora
VERSION_ID=17
PRETTY_NAME="Fedora 17 (Beefy Miracle)"
ANSI_COLOR="0;34"
CPE_NAME="cpe:/o:fedoraproject:fedora:17"
HOME_URL="https://fedoraproject.org/"
BUG_REPORT_URL="https://bugzilla.redhat.com/"</programlisting>
  </refsect1>

  <refsect1>
      <title>See Also</title>
      <para>
        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
        <citerefentry project='die-net'><refentrytitle>lsb_release</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>
      </para>
  </refsect1>

</refentry>