man/os-release.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   5
   6 <refentry id="os-release" xmlns:xi="http://www.w3.org/2001/XInclude">
   7   <refentryinfo>
   8     <title>os-release</title>
   9     <productname>systemd</productname>
  10   </refentryinfo>
  11
  12   <refmeta>
  13     <refentrytitle>os-release</refentrytitle>
  14     <manvolnum>5</manvolnum>
  15   </refmeta>
  16
  17   <refnamediv>
  18     <refname>os-release</refname>
  19     <refname>initrd-release</refname>
  20     <refname>extension-release</refname>
  21     <refpurpose>Operating system identification</refpurpose>
  22   </refnamediv>
  23
  24   <refsynopsisdiv>
  25     <para><filename>/etc/os-release</filename></para>
  26     <para><filename>/usr/lib/os-release</filename></para>
  27     <para><filename>/etc/initrd-release</filename></para>
  28     <para><filename>/usr/lib/extension-release.d/extension-release.<replaceable>IMAGE</replaceable></filename></para>
  29   </refsynopsisdiv>
  30
  31   <refsect1>
  32     <title>Description</title>
  33
  34     <para>The <filename>/etc/os-release</filename> and
  35     <filename>/usr/lib/os-release</filename> files contain operating
  36     system identification data.</para>
  37
  38     <para>The format of <filename>os-release</filename> is a newline-separated list of
  39     environment-like shell-compatible variable assignments. It is possible to source the configuration from
  40     Bourne shell scripts, however, beyond mere variable assignments, no shell features are supported (this
  41     means variable expansion is explicitly not supported), allowing applications to read the file without
  42     implementing a shell compatible execution engine. Variable assignment values must be enclosed in double
  43     or single quotes if they include spaces, semicolons or other special characters outside of A–Z, a–z,
  44     0–9. (Assignments that do not include these special characters may be enclosed in quotes too, but this is
  45     optional.) Shell special characters ("$", quotes, backslash, backtick) must be escaped with backslashes,
  46     following shell style. All strings should be in UTF-8 encoding, and non-printable characters should not
  47     be used. Concatenation of multiple individually quoted strings is not supported. Lines beginning with "#"
  48     are treated as comments. Blank lines are permitted and ignored.</para>
  49
  50     <para>The file <filename>/etc/os-release</filename> takes
  51     precedence over <filename>/usr/lib/os-release</filename>.
  52     Applications should check for the former, and exclusively use its
  53     data if it exists, and only fall back to
  54     <filename>/usr/lib/os-release</filename> if it is missing.
  55     Applications should not read data from both files at the same
  56     time. <filename>/usr/lib/os-release</filename> is the recommended
  57     place to store OS release information as part of vendor trees.
  58     <filename>/etc/os-release</filename> should be a relative symlink
  59     to <filename>/usr/lib/os-release</filename>, to provide
  60     compatibility with applications only looking at
  61     <filename>/etc/</filename>. A relative symlink instead of an
  62     absolute symlink is necessary to avoid breaking the link in a
  63     chroot or initrd environment such as dracut.</para>
  64
  65     <para><filename>os-release</filename> contains data that is
  66     defined by the operating system vendor and should generally not be
  67     changed by the administrator.</para>
  68
  69     <para>As this file only encodes names and identifiers it should
  70     not be localized.</para>
  71
  72     <para>The <filename>/etc/os-release</filename> and
  73     <filename>/usr/lib/os-release</filename> files might be symlinks
  74     to other files, but it is important that the file is available
  75     from earliest boot on, and hence must be located on the root file
  76     system.</para>
  77
  78     <para><filename>os-release</filename> must not contain repeating keys. Nevertheless, readers should pick
  79     the entries later in the file in case of repeats, similarly to how a shell sourcing the file would. A
  80     reader may warn about repeating entries.</para>
  81
  82     <para>For a longer rationale for <filename>os-release</filename>
  83     please refer to the <ulink
  84     url="https://0pointer.de/blog/projects/os-release">Announcement of <filename>/etc/os-release</filename></ulink>.</para>
  85
  86     <refsect2>
  87       <title><filename>/etc/initrd-release</filename></title>
  88
  89       <para>In the <ulink
  90       url="https://docs.kernel.org/admin-guide/initrd.html">initrd</ulink>,
  91       <filename>/etc/initrd-release</filename> plays the same role as <filename>os-release</filename> in the
  92       main system. Additionally, the presence of that file means that the system is in the initrd phase.
  93       <filename>/etc/os-release</filename> should be symlinked to <filename>/etc/initrd-release</filename>
  94       (or vice versa), so programs that only look for <filename>/etc/os-release</filename> (as described
  95       above) work correctly.</para>
  96
  97       <para>The rest of this document that talks about <filename>os-release</filename> should be understood
  98       to apply to <filename>initrd-release</filename> too.</para>
  99     </refsect2>
 100
 101     <refsect2>
 102       <title><filename>/usr/lib/extension-release.d/extension-release.<replaceable>IMAGE</replaceable></filename></title>
 103
 104       <para><filename>/usr/lib/extension-release.d/extension-release.<replaceable>IMAGE</replaceable></filename>
 105       plays the same role for extension images as <filename>os-release</filename> for the main system, and
 106       follows the syntax and rules as described in the <ulink
 107       url="https://systemd.io/PORTABLE_SERVICES">Portable Services Documentation</ulink>. The purpose of this
 108       file is to identify the extension and to allow the operating system to verify that the extension image
 109       matches the base OS. This is typically implemented by checking that the <varname>ID=</varname> options
 110       match, and either <varname>SYSEXT_LEVEL=</varname> exists and matches too, or if it is not present,
 111       <varname>VERSION_ID=</varname> exists and matches. This ensures ABI/API compatibility between the
 112       layers and prevents merging of an incompatible image in an overlay.</para>
 113
 114       <para>In order to identify the extension image itself, the same fields defined below can be added to the
 115       <filename>extension-release</filename> file with a <varname>SYSEXT_</varname> prefix (to disambiguate
 116       from fields used to match on the base image). E.g.: <varname>SYSEXT_ID=myext</varname>,
 117       <varname>SYSEXT_VERSION_ID=1.2.3</varname>.</para>
 118
 119       <para>In the <filename>extension-release.<replaceable>IMAGE</replaceable></filename> filename, the
 120       <replaceable>IMAGE</replaceable> part must exactly match the file name of the containing image with the
 121       suffix removed. In case it is not possible to guarantee that an image file name is stable and doesn't
 122       change between the build and the deployment phases, it is possible to relax this check: if exactly one
 123       file whose name matches <literal><filename>extension-release.*</filename></literal> is present in this
 124       directory, and the file is tagged with a <varname>user.extension-release.strict</varname>
 125       <citerefentry project='man-pages'><refentrytitle>xattr</refentrytitle><manvolnum>7</manvolnum></citerefentry> set to the
 126       string <literal>0</literal>, it will be used instead.</para>
 127
 128       <para>The rest of this document that talks about <filename>os-release</filename> should be understood
 129       to apply to <filename>extension-release</filename> too.</para>
 130     </refsect2>
 131   </refsect1>
 132
 133   <refsect1>
 134     <title>Options</title>
 135
 136     <para>The following OS identifications parameters may be set using
 137     <filename>os-release</filename>:</para>
 138
 139     <refsect2>
 140       <title>General information identifying the operating system</title>
 141
 142       <variablelist class='environment-variables'>
 143         <varlistentry>
 144           <term><varname>NAME=</varname></term>
 145
 146           <listitem><para>A string identifying the operating system, without a version component, and
 147           suitable for presentation to the user. If not set, a default of <literal>NAME=Linux</literal> may
 148           be used.</para>
 149
 150           <para>Examples: <literal>NAME=Fedora</literal>, <literal>NAME="Debian GNU/Linux"</literal>.
 151           </para></listitem>
 152         </varlistentry>
 153
 154         <varlistentry>
 155           <term><varname>ID=</varname></term>
 156
 157           <listitem><para>A lower-case string (no spaces or other characters outside of 0–9, a–z, ".", "_"
 158           and "-") identifying the operating system, excluding any version information and suitable for
 159           processing by scripts or usage in generated filenames. If not set, a default of
 160           <literal>ID=linux</literal> may be used. Note that even though this string may not include
 161           characters that require shell quoting, quoting may nevertheless be used.</para>
 162
 163           <para>Examples: <literal>ID=fedora</literal>, <literal>ID=debian</literal>.</para></listitem>
 164         </varlistentry>
 165
 166         <varlistentry>
 167           <term><varname>ID_LIKE=</varname></term>
 168
 169           <listitem><para>A space-separated list of operating system identifiers in the same syntax as the
 170           <varname>ID=</varname> setting. It should list identifiers of operating systems that are closely
 171           related to the local operating system in regards to packaging and programming interfaces, for
 172           example listing one or more OS identifiers the local OS is a derivative from.  An OS should
 173           generally only list other OS identifiers it itself is a derivative of, and not any OSes that are
 174           derived from it, though symmetric relationships are possible. Build scripts and similar should
 175           check this variable if they need to identify the local operating system and the value of
 176           <varname>ID=</varname> is not recognized. Operating systems should be listed in order of how
 177           closely the local operating system relates to the listed ones, starting with the closest. This
 178           field is optional.</para>
 179
 180           <para>Examples: for an operating system with <literal>ID=centos</literal>, an assignment of
 181           <literal>ID_LIKE="rhel fedora"</literal> would be appropriate. For an operating system with
 182           <literal>ID=ubuntu</literal>, an assignment of <literal>ID_LIKE=debian</literal> is appropriate.
 183           </para></listitem>
 184         </varlistentry>
 185
 186         <varlistentry>
 187           <term><varname>PRETTY_NAME=</varname></term>
 188
 189           <listitem><para>A pretty operating system name in a format suitable for presentation to the
 190           user. May or may not contain a release code name or OS version of some kind, as suitable. If not
 191           set, a default of <literal>PRETTY_NAME="Linux"</literal> may be used</para>
 192
 193           <para>Example: <literal>PRETTY_NAME="Fedora 17 (Beefy Miracle)"</literal>.</para></listitem>
 194         </varlistentry>
 195
 196         <varlistentry>
 197           <term><varname>CPE_NAME=</varname></term>
 198
 199           <listitem><para>A CPE name for the operating system, in URI binding syntax, following the <ulink
 200           url="http://scap.nist.gov/specifications/cpe/">Common Platform Enumeration Specification</ulink> as
 201           proposed by the NIST. This field is optional.</para>
 202
 203           <para>Example: <literal>CPE_NAME="cpe:/o:fedoraproject:fedora:17"</literal></para></listitem>
 204         </varlistentry>
 205
 206         <varlistentry>
 207           <term><varname>VARIANT=</varname></term>
 208
 209           <listitem><para>A string identifying a specific variant or edition of the operating system suitable
 210           for presentation to the user. This field may be used to inform the user that the configuration of
 211           this system is subject to a specific divergent set of rules or default configuration settings. This
 212           field is optional and may not be implemented on all systems.</para>
 213
 214           <para>Examples: <literal>VARIANT="Server Edition"</literal>, <literal>VARIANT="Smart Refrigerator
 215           Edition"</literal>.</para>
 216
 217           <para>Note: this field is for display purposes only. The <varname>VARIANT_ID</varname> field should
 218           be used for making programmatic decisions.</para></listitem>
 219         </varlistentry>
 220
 221         <varlistentry>
 222           <term><varname>VARIANT_ID=</varname></term>
 223
 224           <listitem><para>A lower-case string (no spaces or other characters outside of 0–9, a–z, ".", "_" and
 225           "-"), identifying a specific variant or edition of the operating system. This may be interpreted by
 226           other packages in order to determine a divergent default configuration. This field is optional and
 227           may not be implemented on all systems.</para>
 228
 229           <para>Examples: <literal>VARIANT_ID=server</literal>, <literal>VARIANT_ID=embedded</literal>.
 230           </para></listitem>
 231         </varlistentry>
 232       </variablelist>
 233     </refsect2>
 234
 235     <refsect2>
 236       <title>Information about the version of the operating system</title>
 237
 238       <variablelist class='environment-variables'>
 239         <varlistentry>
 240           <term><varname>VERSION=</varname></term>
 241
 242           <listitem><para>A string identifying the operating system version, excluding any OS name
 243           information, possibly including a release code name, and suitable for presentation to the
 244           user. This field is optional.</para>
 245
 246           <para>Examples: <literal>VERSION=17</literal>, <literal>VERSION="17 (Beefy Miracle)"</literal>.
 247           </para></listitem>
 248         </varlistentry>
 249
 250         <varlistentry>
 251           <term><varname>VERSION_ID=</varname></term>
 252
 253           <listitem><para>A lower-case string (mostly numeric, no spaces or other characters outside of 0–9,
 254           a–z, ".", "_" and "-") identifying the operating system version, excluding any OS name information
 255           or release code name, and suitable for processing by scripts or usage in generated filenames. This
 256           field is optional.</para>
 257
 258           <para>Examples: <literal>VERSION_ID=17</literal>, <literal>VERSION_ID=11.04</literal>.
 259           </para></listitem>
 260         </varlistentry>
 261
 262         <varlistentry>
 263           <term><varname>VERSION_CODENAME=</varname></term>
 264
 265           <listitem><para>A lower-case string (no spaces or other characters outside of 0–9, a–z, ".", "_"
 266           and "-") identifying the operating system release code name, excluding any OS name information or
 267           release version, and suitable for processing by scripts or usage in generated filenames. This field
 268           is optional and may not be implemented on all systems.</para>
 269
 270           <para>Examples: <literal>VERSION_CODENAME=buster</literal>,
 271           <literal>VERSION_CODENAME=xenial</literal>.</para></listitem>
 272         </varlistentry>
 273
 274         <varlistentry>
 275           <term><varname>BUILD_ID=</varname></term>
 276
 277           <listitem><para>A string uniquely identifying the system image originally used as the installation
 278           base. In most cases, <varname>VERSION_ID</varname> or
 279           <varname>IMAGE_ID</varname>+<varname>IMAGE_VERSION</varname> are updated when the entire system
 280           image is replaced during an update. <varname>BUILD_ID</varname> may be used in distributions where
 281           the original installation image version is important: <varname>VERSION_ID</varname> would change
 282           during incremental system updates, but <varname>BUILD_ID</varname> would not. This field is
 283           optional.</para>
 284
 285           <para>Examples: <literal>BUILD_ID="2013-03-20.3"</literal>, <literal>BUILD_ID=201303203</literal>.
 286           </para></listitem>
 287         </varlistentry>
 288
 289         <varlistentry>
 290           <term><varname>IMAGE_ID=</varname></term>
 291
 292           <listitem><para> A lower-case string (no spaces or other characters outside of 0–9, a–z, ".", "_"
 293           and "-"), identifying a specific image of the operating system. This is supposed to be used for
 294           environments where OS images are prepared, built, shipped and updated as comprehensive, consistent
 295           OS images. This field is optional and may not be implemented on all systems, in particularly not on
 296           those that are not managed via images but put together and updated from individual packages and on
 297           the local system.</para>
 298
 299           <para>Examples: <literal>IMAGE_ID=vendorx-cashier-system</literal>,
 300           <literal>IMAGE_ID=netbook-image</literal>.</para>
 301
 302           <xi:include href="version-info.xml" xpointer="v249"/></listitem>
 303         </varlistentry>
 304
 305         <varlistentry>
 306           <term><varname>IMAGE_VERSION=</varname></term>
 307
 308           <listitem><para>A lower-case string (mostly numeric, no spaces or other characters outside of 0–9,
 309           a–z, ".", "_" and "-") identifying the OS image version. This is supposed to be used together with
 310           <varname>IMAGE_ID</varname> described above, to discern different versions of the same image.
 311           </para>
 312
 313           <para>Examples: <literal>IMAGE_VERSION=33</literal>, <literal>IMAGE_VERSION=47.1rc1</literal>.
 314           </para>
 315
 316           <xi:include href="version-info.xml" xpointer="v249"/></listitem>
 317         </varlistentry>
 318       </variablelist>
 319
 320       <para>To summarize: if the image updates are built and shipped as comprehensive units,
 321       <varname>IMAGE_ID</varname>+<varname>IMAGE_VERSION</varname> is the best fit. Otherwise, if updates
 322       eventually completely replace previously installed contents, as in a typical binary distribution,
 323       <varname>VERSION_ID</varname> should be used to identify major releases of the operating system.
 324       <varname>BUILD_ID</varname> may be used instead or in addition to <varname>VERSION_ID</varname> when
 325       the original system image version is important.</para>
 326     </refsect2>
 327
 328     <refsect2>
 329       <title>Presentation information and links</title>
 330
 331       <variablelist class='environment-variables'>
 332         <varlistentry>
 333           <term><varname>HOME_URL=</varname></term>
 334           <term><varname>DOCUMENTATION_URL=</varname></term>
 335           <term><varname>SUPPORT_URL=</varname></term>
 336           <term><varname>BUG_REPORT_URL=</varname></term>
 337           <term><varname>PRIVACY_POLICY_URL=</varname></term>
 338
 339           <listitem><para>Links to resources on the Internet related to the operating system.
 340           <varname>HOME_URL=</varname> should refer to the homepage of the operating system, or alternatively
 341           some homepage of the specific version of the operating system.
 342           <varname>DOCUMENTATION_URL=</varname> should refer to the main documentation page for this
 343           operating system.  <varname>SUPPORT_URL=</varname> should refer to the main support page for the
 344           operating system, if there is any. This is primarily intended for operating systems which vendors
 345           provide support for. <varname>BUG_REPORT_URL=</varname> should refer to the main bug reporting page
 346           for the operating system, if there is any. This is primarily intended for operating systems that
 347           rely on community QA. <varname>PRIVACY_POLICY_URL=</varname> should refer to the main privacy
 348           policy page for the operating system, if there is any. These settings are optional, and providing
 349           only some of these settings is common. These URLs are intended to be exposed in "About this system"
 350           UIs behind links with captions such as "About this Operating System", "Obtain Support", "Report a
 351           Bug", or "Privacy Policy". The values should be in <ulink
 352           url="https://tools.ietf.org/html/rfc3986">RFC3986 format</ulink>, and should be
 353           <literal>http:</literal> or <literal>https:</literal> URLs, and possibly <literal>mailto:</literal>
 354           or <literal>tel:</literal>. Only one URL shall be listed in each setting. If multiple resources
 355           need to be referenced, it is recommended to provide an online landing page linking all available
 356           resources.</para>
 357
 358           <para>Examples: <literal>HOME_URL="https://fedoraproject.org/"</literal>,
 359           <literal>BUG_REPORT_URL="https://bugzilla.redhat.com/"</literal>.</para></listitem>
 360         </varlistentry>
 361
 362         <varlistentry>
 363           <term><varname>SUPPORT_END=</varname></term>
 364
 365           <listitem><para>The date at which support for this version of the OS ends. (What exactly "lack of
 366           support" means varies between vendors, but generally users should assume that updates, including
 367           security fixes, will not be provided.) The value is a date in the ISO 8601 format
 368           <literal>YYYY-MM-DD</literal>, and specifies the first day on which support <emphasis>is
 369           not</emphasis> provided.</para>
 370
 371           <para>For example, <literal>SUPPORT_END=2001-01-01</literal> means that the system was supported
 372           until the end of the last day of the previous millennium.</para>
 373
 374           <xi:include href="version-info.xml" xpointer="v252"/></listitem>
 375         </varlistentry>
 376
 377         <varlistentry>
 378           <term><varname>LOGO=</varname></term>
 379
 380           <listitem><para>A string, specifying the name of an icon as defined by <ulink
 381           url="https://standards.freedesktop.org/icon-theme-spec/latest">freedesktop.org Icon Theme
 382           Specification</ulink>. This can be used by graphical applications to display an operating system's
 383           or distributor's logo. This field is optional and may not necessarily be implemented on all
 384           systems.</para>
 385
 386           <para>Examples: <literal>LOGO=fedora-logo</literal>, <literal>LOGO=distributor-logo-opensuse</literal>
 387           </para></listitem>
 388         </varlistentry>
 389
 390         <varlistentry>
 391           <term><varname>ANSI_COLOR=</varname></term>
 392
 393           <listitem><para>A suggested presentation color when showing the OS name on the console. This should
 394           be specified as string suitable for inclusion in the ESC [ m ANSI/ECMA-48 escape code for setting
 395           graphical rendition. This field is optional.</para>
 396
 397           <para>Examples: <literal>ANSI_COLOR="0;31"</literal> for red, <literal>ANSI_COLOR="1;34"</literal>
 398           for light blue, or <literal>ANSI_COLOR="0;38;2;60;110;180"</literal> for Fedora blue.
 399           </para></listitem>
 400         </varlistentry>
 401
 402         <varlistentry>
 403           <term><varname>VENDOR_NAME=</varname></term>
 404
 405           <listitem><para>The name of the OS vendor. This is the name of the organization or company which
 406           produces the OS. This field is optional.</para>
 407
 408           <para>This name is intended to be exposed in "About this system" UIs or software update UIs when
 409           needed to distinguish the OS vendor from the OS itself. It is intended to be human readable.</para>
 410
 411           <para>Examples: <literal>VENDOR_NAME="Fedora Project"</literal> for Fedora Linux,
 412           <literal>VENDOR_NAME="Canonical"</literal> for Ubuntu.</para>
 413
 414           <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 415         </varlistentry>
 416
 417         <varlistentry>
 418           <term><varname>VENDOR_URL=</varname></term>
 419
 420           <listitem><para>The homepage of the OS vendor. This field is optional. The
 421           <varname>VENDOR_NAME=</varname> field should be set if this one is, although clients must be
 422           robust against either field not being set.</para>
 423
 424           <para>The value should be in <ulink
 425           url="https://tools.ietf.org/html/rfc3986">RFC3986 format</ulink>, and should be
 426           <literal>http:</literal> or <literal>https:</literal> URLs. Only one URL shall be listed in the
 427           setting.</para>
 428
 429           <para>Examples: <literal>VENDOR_URL="https://fedoraproject.org/"</literal>,
 430           <literal>VENDOR_URL="https://canonical.com/"</literal>.</para>
 431
 432           <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 433         </varlistentry>
 434       </variablelist>
 435     </refsect2>
 436
 437     <refsect2>
 438       <title>Distribution-level defaults and metadata</title>
 439
 440       <variablelist class='environment-variables'>
 441         <varlistentry>
 442           <term><varname>DEFAULT_HOSTNAME=</varname></term>
 443
 444           <listitem><para>A string specifying the hostname if
 445           <citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>5</manvolnum></citerefentry> is not
 446           present and no other configuration source specifies the hostname. Must be either a single DNS label
 447           (a string composed of 7-bit ASCII lower-case characters and no spaces or dots, limited to the
 448           format allowed for DNS domain name labels), or a sequence of such labels separated by single dots
 449           that forms a valid DNS FQDN. The hostname must be at most 64 characters, which is a Linux
 450           limitation (DNS allows longer names).</para>
 451
 452           <para>See <citerefentry><refentrytitle>org.freedesktop.hostname1</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 453           for a description of how
 454           <citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 455           determines the fallback hostname.</para></listitem>
 456         </varlistentry>
 457
 458         <varlistentry>
 459           <term><varname>ARCHITECTURE=</varname></term>
 460           <listitem><para>A string that specifies which CPU architecture the userspace binaries require.
 461           The architecture identifiers are the same as for <varname>ConditionArchitecture=</varname>
 462           described in <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 463           The field is optional and should only be used when just single architecture is supported.
 464           It may provide redundant information when used in a GPT partition with a GUID type that already
 465           encodes the architecture. If this is not the case, the architecture should be specified in
 466           e.g., an extension image, to prevent an incompatible host from loading it.
 467           </para>
 468
 469           <xi:include href="version-info.xml" xpointer="v252"/></listitem>
 470         </varlistentry>
 471
 472         <varlistentry>
 473           <term><varname>SYSEXT_LEVEL=</varname></term>
 474
 475           <listitem><para>A lower-case string (mostly numeric, no spaces or other characters outside of 0–9,
 476           a–z, ".", "_" and "-") identifying the operating system extensions support level, to indicate which
 477           extension images are supported. See <filename>/usr/lib/extension-release.d/extension-release.<replaceable>IMAGE</replaceable></filename>,
 478           <ulink url="https://docs.kernel.org/admin-guide/initrd.html">initrd</ulink> and
 479           <citerefentry><refentrytitle>systemd-sysext</refentrytitle><manvolnum>8</manvolnum></citerefentry>)
 480           for more information.</para>
 481
 482           <para>Examples: <literal>SYSEXT_LEVEL=2</literal>, <literal>SYSEXT_LEVEL=15.14</literal>.
 483           </para></listitem>
 484         </varlistentry>
 485
 486         <varlistentry>
 487           <term><varname>CONFEXT_LEVEL=</varname></term>
 488
 489           <listitem><para>Semantically the same as <varname>SYSEXT_LEVEL=</varname> but for confext images.
 490           See <filename>/etc/extension-release.d/extension-release.<replaceable>IMAGE</replaceable></filename>
 491           for more information.</para>
 492
 493           <para>Examples: <literal>CONFEXT_LEVEL=2</literal>, <literal>CONFEXT_LEVEL=15.14</literal>.
 494           </para>
 495
 496           <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 497         </varlistentry>
 498
 499         <varlistentry>
 500           <term><varname>SYSEXT_SCOPE=</varname></term>
 501           <listitem><para>Takes a space-separated list of one or more of the strings
 502           <literal>system</literal>, <literal>initrd</literal> and <literal>portable</literal>. This field is
 503           only supported in <filename>extension-release.d/</filename> files and indicates what environments
 504           the system extension is applicable to: i.e. to regular systems, to initrds, or to portable service
 505           images. If unspecified, <literal>SYSEXT_SCOPE=system portable</literal> is implied, i.e. any system
 506           extension without this field is applicable to regular systems and to portable service environments,
 507           but not to initrd environments.</para>
 508
 509           <xi:include href="version-info.xml" xpointer="v250"/></listitem>
 510         </varlistentry>
 511
 512         <varlistentry>
 513           <term><varname>CONFEXT_SCOPE=</varname></term>
 514
 515           <listitem><para>Semantically the same as <varname>SYSEXT_SCOPE=</varname> but for confext images.</para>
 516
 517           <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 518         </varlistentry>
 519
 520         <varlistentry>
 521           <term><varname>PORTABLE_PREFIXES=</varname></term>
 522           <listitem><para>Takes a space-separated list of one or more valid prefix match strings for the
 523           <ulink url="https://systemd.io/PORTABLE_SERVICES">Portable Services Documentation</ulink> logic.
 524           This field serves two purposes: it is informational, identifying portable service images as such
 525           (and thus allowing them to be distinguished from other OS images, such as bootable system images).
 526           It is also used when a portable service image is attached: the specified or implied portable
 527           service prefix is checked against the list specified here, to enforce restrictions how images may
 528           be attached to a system.</para>
 529
 530           <xi:include href="version-info.xml" xpointer="v250"/></listitem>
 531         </varlistentry>
 532       </variablelist>
 533     </refsect2>
 534
 535     <refsect2>
 536       <title>Notes</title>
 537
 538       <para>If you are using this file to determine the OS or a specific version of it, use the
 539       <varname>ID</varname> and <varname>VERSION_ID</varname> fields, possibly with
 540       <varname>ID_LIKE</varname> as fallback for <varname>ID</varname>. When looking for an OS identification
 541       string for presentation to the user use the <varname>PRETTY_NAME</varname> field.</para>
 542
 543       <para>Note that operating system vendors may choose not to provide version information, for example to
 544       accommodate for rolling releases. In this case, <varname>VERSION</varname> and
 545       <varname>VERSION_ID</varname> may be unset. Applications should not rely on these fields to be
 546       set.</para>
 547
 548       <para>Operating system vendors may extend the file format and introduce new fields. It is highly
 549       recommended to prefix new fields with an OS specific name in order to avoid name clashes. Applications
 550       reading this file must ignore unknown fields.</para>
 551
 552       <para>Example: <literal>DEBIAN_BTS="debbugs://bugs.debian.org/"</literal>.</para>
 553
 554       <para>Container and sandbox runtime managers may make the host's identification data available to
 555       applications by providing the host's <filename>/etc/os-release</filename> (if available, otherwise
 556       <filename>/usr/lib/os-release</filename> as a fallback) as
 557       <filename>/run/host/os-release</filename>.</para>
 558     </refsect2>
 559   </refsect1>
 560
 561   <refsect1>
 562     <title>Examples</title>
 563
 564     <example>
 565       <title><filename>os-release</filename> file for Fedora Workstation</title>
 566
 567       <programlisting>NAME=Fedora
 568 VERSION="32 (Workstation Edition)"
 569 ID=fedora
 570 VERSION_ID=32
 571 PRETTY_NAME="Fedora 32 (Workstation Edition)"
 572 ANSI_COLOR="0;38;2;60;110;180"
 573 LOGO=fedora-logo-icon
 574 CPE_NAME="cpe:/o:fedoraproject:fedora:32"
 575 HOME_URL="https://fedoraproject.org/"
 576 DOCUMENTATION_URL="https://docs.fedoraproject.org/en-US/fedora/f32/system-administrators-guide/"
 577 SUPPORT_URL="https://fedoraproject.org/wiki/Communicating_and_getting_help"
 578 BUG_REPORT_URL="https://bugzilla.redhat.com/"
 579 REDHAT_BUGZILLA_PRODUCT="Fedora"
 580 REDHAT_BUGZILLA_PRODUCT_VERSION=32
 581 REDHAT_SUPPORT_PRODUCT="Fedora"
 582 REDHAT_SUPPORT_PRODUCT_VERSION=32
 583 PRIVACY_POLICY_URL="https://fedoraproject.org/wiki/Legal:PrivacyPolicy"
 584 VARIANT="Workstation Edition"
 585 VARIANT_ID=workstation</programlisting>
 586     </example>
 587
 588     <example>
 589       <title><filename>extension-release</filename> file for an extension for Fedora Workstation 32</title>
 590
 591       <programlisting>ID=fedora
 592 VERSION_ID=32</programlisting>
 593     </example>
 594
 595     <example>
 596       <title>Reading <filename>os-release</filename> in
 597       <citerefentry project='man-pages'><refentrytitle>sh</refentrytitle><manvolnum>1</manvolnum></citerefentry></title>
 598
 599       <programlisting><xi:include href="check-os-release.sh" parse="text" /></programlisting>
 600     </example>
 601
 602     <example>
 603       <title>Reading <filename>os-release</filename> in
 604       <citerefentry project='die-net'><refentrytitle>python</refentrytitle><manvolnum>1</manvolnum></citerefentry> (versions &gt;= 3.10)</title>
 605
 606       <programlisting><xi:include href="check-os-release-simple.py" parse="text" /></programlisting>
 607
 608       <para>See docs for <ulink url="https://docs.python.org/3/library/platform.html#platform.freedesktop_os_release">
 609       <function>platform.freedesktop_os_release</function></ulink> for more details.
 610       </para>
 611     </example>
 612
 613     <example>
 614       <title>Reading <filename>os-release</filename> in
 615       <citerefentry project='die-net'><refentrytitle>python</refentrytitle><manvolnum>1</manvolnum></citerefentry> (any version)</title>
 616
 617       <programlisting><xi:include href="check-os-release.py" parse="text" /></programlisting>
 618
 619       <para>Note that the above version that uses the built-in implementation is preferred
 620       in most cases, and the open-coded version here is provided for reference.</para>
 621     </example>
 622
 623   </refsect1>
 624
 625   <refsect1>
 626       <title>See Also</title>
 627       <para>
 628         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 629         <citerefentry project='die-net'><refentrytitle>lsb_release</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 630         <citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 631         <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 632         <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 633       </para>
 634   </refsect1>
 635
 636 </refentry>