Ubuntu Manpage: os-release, initrd-release, extension-release

Provided by: systemd_251.4-1ubuntu7_amd64

NAME

       os-release, initrd-release, extension-release - Operating system identification

SYNOPSIS

       /etc/os-release

       /usr/lib/os-release

       /etc/initrd-release

       /usr/lib/extension-release.d/extension-release.IMAGE

DESCRIPTION

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

The format of os-release is a newline-separated list of environment-like shell-compatible
variable assignments. It is possible to source the configuration from Bourne 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. (Assignments that do not include these
special characters may be enclosed in quotes too, but this is optional.) Shell special
characters ("$", quotes, backslash, backtick) must be escaped with backslashes, following
shell style. All strings should be in UTF-8 encoding, and non-printable characters should
not be used. Concatenation of multiple individually quoted strings is not supported. Lines
beginning with "#" are treated as comments. Blank lines are permitted and ignored.

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

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

As this file only encodes names and identifiers it should not be localized.

The /etc/os-release and /usr/lib/os-release 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.

os-release must not contain repeating keys. Nevertheless, readers should pick the entries
later in the file in case of repeats, similarly to how a shell sourcing the file would. A
reader may warn about repeating entries.

For a longer rationale for os-release please refer to the Announcement of
/etc/os-release[1].

/etc/initrd-release
In the initrd[2], /etc/initrd-release plays the same role as os-release in the main
system. Additionally, the presence of that file means that the system is in the initrd
phase. /etc/os-release should be symlinked to /etc/initrd-release (or vice versa), so
programs that only look for /etc/os-release (as described above) work correctly.

The rest of this document that talks about os-release should be understood to apply to
initrd-release too.

/usr/lib/extension-release.d/extension-release.IMAGE
/usr/lib/extension-release.d/extension-release.IMAGE plays the same role for extension
images as os-release for the main system, and follows the syntax and rules as described in
the Portable Services Documentation[3]. The purpose of this file is to identify the
extension and to allow the operating system to verify that the extension image matches the
base OS. This is typically implemented by checking that the ID= options match, and either
SYSEXT_LEVEL= exists and matches too, or if it is not present, VERSION_ID= exists and
matches. This ensures ABI/API compatibility between the layers and prevents merging of an
incompatible image in an overlay.

In the extension-release.IMAGE filename, the IMAGE part must exactly match the file name
of the containing image with the suffix removed. In case it is not possible to guarantee
that an image file name is stable and doesn't change between the build and the deployment
phases, it is possible to relax this check: if exactly one file whose name matches
"extension-release.*" is present in this directory, and the file is tagged with a
user.extension-release.strict xattr(7) set to the string "0", it will be used instead.

The rest of this document that talks about os-release should be understood to apply to
extension-release too.

OPTIONS

The following OS identifications parameters may be set using os-release:

General information identifying the operating system
NAME=
A string identifying the operating system, without a version component, and suitable
for presentation to the user. If not set, a default of "NAME=Linux" may be used.

Examples: "NAME=Fedora", "NAME="Debian GNU/Linux"".

ID=
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, a default of
"ID=linux" may be used. Note that even though this string may not include characters
that require shell quoting, quoting may nevertheless be used.

Examples: "ID=fedora", "ID=debian".

ID_LIKE=
A space-separated list of operating system identifiers in the same syntax as the ID=
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 ID= 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.

Examples: for an operating system with "ID=centos", an assignment of "ID_LIKE="rhel
fedora"" would be appropriate. For an operating system with "ID=ubuntu", an assignment
of "ID_LIKE=debian" is appropriate.

PRETTY_NAME=
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, a default of "PRETTY_NAME="Linux"" may be used

Example: "PRETTY_NAME="Fedora 17 (Beefy Miracle)"".

CPE_NAME=
A CPE name for the operating system, in URI binding syntax, following the Common
Platform Enumeration Specification[4] as proposed by the NIST. This field is optional.

Example: "CPE_NAME="cpe:/o:fedoraproject:fedora:17""

VARIANT=
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: "VARIANT="Server Edition"", "VARIANT="Smart Refrigerator Edition"".

Note: this field is for display purposes only. The VARIANT_ID field should be used for
making programmatic decisions.

VARIANT_ID=
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: "VARIANT_ID=server", "VARIANT_ID=embedded".

Information about the version of the operating system
VERSION=
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.

Examples: "VERSION=17", "VERSION="17 (Beefy Miracle)"".

VERSION_ID=
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.

Examples: "VERSION_ID=17", "VERSION_ID=11.04".

VERSION_CODENAME=
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: "VERSION_CODENAME=buster", "VERSION_CODENAME=xenial".

BUILD_ID=
A string uniquely identifying the system image originally used as the installation
base. In most cases, VERSION_ID or IMAGE_ID+IMAGE_VERSION are updated when the entire
system image is replaced during an update. BUILD_ID may be used in distributions
where the original installation image version is important: VERSION_ID would change
during incremental system updates, but BUILD_ID would not. This field is optional.

Examples: "BUILD_ID="2013-03-20.3"", "BUILD_ID=201303203".

IMAGE_ID=
A lower-case string (no spaces or other characters outside of 0–9, a–z, ".", "_" and
"-"), identifying a specific image of the operating system. This is supposed to be
used for environments where OS images are prepared, built, shipped and updated as
comprehensive, consistent OS images. This field is optional and may not be implemented
on all systems, in particularly not on those that are not managed via images but put
together and updated from individual packages and on the local system.

Examples: "IMAGE_ID=vendorx-cashier-system", "IMAGE_ID=netbook-image".

IMAGE_VERSION=
A lower-case string (mostly numeric, no spaces or other characters outside of 0–9,
a–z, ".", "_" and "-") identifying the OS image version. This is supposed to be used
together with IMAGE_ID described above, to discern different versions of the same
image.

Examples: "IMAGE_VERSION=33", "IMAGE_VERSION=47.1rc1".

To summarize: if the image updates are built and shipped as comprehensive units,
IMAGE_ID+IMAGE_VERSION is the best fit. Otherwise, if updates eventually completely
replace previously installed contents, as in a typical binary distribution, VERSION_ID
should be used to identify major releases of the operating system. BUILD_ID may be used
instead or in addition to VERSION_ID when the original system image version is important.

Presentation information and links
HOME_URL=, DOCUMENTATION_URL=, SUPPORT_URL=, BUG_REPORT_URL=, PRIVACY_POLICY_URL=
Links to resources on the Internet related to the operating system. HOME_URL= should
refer to the homepage of the operating system, or alternatively some homepage of the
specific version of the operating system. DOCUMENTATION_URL= should refer to the main
documentation page for this operating system. SUPPORT_URL= 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. BUG_REPORT_URL= 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.
PRIVACY_POLICY_URL= should refer to the main privacy policy page for the operating
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 RFC3986 format[5], and
should be "http:" or "https:" URLs, and possibly "mailto:" or "tel:". 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: "HOME_URL="https://fedoraproject.org/"",
"BUG_REPORT_URL="https://bugzilla.redhat.com/"".

LOGO=
A string, specifying the name of an icon as defined by freedesktop.org Icon Theme
Specification[6]. This can be used by graphical applications to display an operating
system's or distributor's logo. This field is optional and may not necessarily be
implemented on all systems.

Examples: "LOGO=fedora-logo", "LOGO=distributor-logo-opensuse"

ANSI_COLOR=
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.

Examples: "ANSI_COLOR="0;31"" for red, "ANSI_COLOR="1;34"" for light blue, or
"ANSI_COLOR="0;38;2;60;110;180"" for Fedora blue.

Distribution-level defaults and metadata
DEFAULT_HOSTNAME=
A string specifying the hostname if hostname(5) is not present and no other
configuration source specifies the hostname. Must be either a single DNS label (a
string composed of 7-bit ASCII lower-case characters and no spaces or dots, limited to
the format allowed for DNS domain name labels), or a sequence of such labels separated
by single dots that forms a valid DNS FQDN. The hostname must be at most 64
characters, which is a Linux limitation (DNS allows longer names).

See org.freedesktop.hostname1(5) for a description of how systemd-hostnamed.service(8)
determines the fallback hostname.

SYSEXT_LEVEL=
A lower-case string (mostly numeric, no spaces or other characters outside of 0–9,
a–z, ".", "_" and "-") identifying the operating system extensions support level, to
indicate which extension images are supported. See
/usr/lib/extension-release.d/extension-release.IMAGE, initrd[2] and systemd-sysext(8))
for more information.

Examples: "SYSEXT_LEVEL=2", "SYSEXT_LEVEL=15.14".

SYSEXT_SCOPE=
Takes a space-separated list of one or more of the strings "system", "initrd" and
"portable". This field is only supported in extension-release.d/ files and indicates
what environments the system extension is applicable to: i.e. to regular systems, to
initial RAM filesystems ("initrd") or to portable service images. If unspecified,
"SYSEXT_SCOPE=system portable" is implied, i.e. any system extension without this
field is applicable to regular systems and to portable service environments, but not
to initrd environments.

PORTABLE_PREFIXES=
Takes a space-separated list of one or more valid prefix match strings for the
Portable Services[3] logic. This field serves two purposes: it is informational,
identifying portable service images as such (and thus allowing them to be
distinguished from other OS images, such as bootable system images). It is also used
when a portable service image is attached: the specified or implied portable service
prefix is checked against the list specified here, to enforce restrictions how images
may be attached to a system.

Notes
If you are using this file to determine the OS or a specific version of it, use the ID and
VERSION_ID fields, possibly with ID_LIKE as fallback for ID. When looking for an OS
identification string for presentation to the user use the PRETTY_NAME field.

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

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: "DEBIAN_BTS="debbugs://bugs.debian.org/"".

Container and sandbox runtime managers may make the host's identification data available
to applications by providing the host's /etc/os-release (if available, otherwise
/usr/lib/os-release as a fallback) as /run/host/os-release.

EXAMPLES

       Example 1. os-release file for Fedora Workstation

           NAME=Fedora
           VERSION="32 (Workstation Edition)"
           ID=fedora
           VERSION_ID=32
           PRETTY_NAME="Fedora 32 (Workstation Edition)"
           ANSI_COLOR="0;38;2;60;110;180"
           LOGO=fedora-logo-icon
           CPE_NAME="cpe:/o:fedoraproject:fedora:32"
           HOME_URL="https://fedoraproject.org/"
           DOCUMENTATION_URL="https://docs.fedoraproject.org/en-US/fedora/f32/system-administrators-guide/"
           SUPPORT_URL="https://fedoraproject.org/wiki/Communicating_and_getting_help"
           BUG_REPORT_URL="https://bugzilla.redhat.com/"
           REDHAT_BUGZILLA_PRODUCT="Fedora"
           REDHAT_BUGZILLA_PRODUCT_VERSION=32
           REDHAT_SUPPORT_PRODUCT="Fedora"
           REDHAT_SUPPORT_PRODUCT_VERSION=32
           PRIVACY_POLICY_URL="https://fedoraproject.org/wiki/Legal:PrivacyPolicy"
           VARIANT="Workstation Edition"
           VARIANT_ID=workstation

       Example 2. extension-release file for an extension for Fedora Workstation 32

           ID=fedora
           VERSION_ID=32

       Example 3. Reading os-release in sh(1)

           #!/bin/sh -eu
           # SPDX-License-Identifier: CC0-1.0

           test -e /etc/os-release && os_release='/etc/os-release' || os_release='/usr/lib/os-release'
           . "${os_release}"

           echo "Running on ${PRETTY_NAME:-Linux}"

           if [ "${ID:-linux}" = "debian" ] || [ "${ID_LIKE#*debian*}" != "${ID_LIKE}" ]; then
               echo "Looks like Debian!"
           fi

       Example 4. Reading os-release in python(1) (versions >= 3.10)

           #!/usr/bin/python
           # SPDX-License-Identifier: CC0-1.0

           import platform
           os_release = platform.freedesktop_os_release()

           pretty_name = os_release.get('PRETTY_NAME', 'Linux')
           print(f'Running on {pretty_name!r}')

           if 'fedora' in [os_release.get('ID', 'linux'),
                           *os_release.get('ID_LIKE', '').split()]:
               print('Looks like Fedora!')

       See docs for platform.freedesktop_os_release[7] for more details.

       Example 5. Reading os-release in python(1) (any version)

           #!/usr/bin/python
           # SPDX-License-Identifier: CC0-1.0

           import ast
           import re
           import sys

           def read_os_release():
               try:
                   filename = '/etc/os-release'
                   f = open(filename)
               except FileNotFoundError:
                   filename = '/usr/lib/os-release'
                   f = open(filename)

               for line_number, line in enumerate(f, start=1):
                   line = line.rstrip()
                   if not line or line.startswith('#'):
                       continue
                   if m := re.match(r'([A-Z][A-Z_0-9]+)=(.*)', line):
                       name, val = m.groups()
                       if val and val[0] in '"\'':
                           val = ast.literal_eval(val)
                       yield name, val
                   else:
                       print(f'{filename}:{line_number}: bad line {line!r}',
                             file=sys.stderr)

           os_release = dict(read_os_release())

           pretty_name = os_release.get('PRETTY_NAME', 'Linux')
           print(f'Running on {pretty_name!r}')

           if 'debian' in [os_release.get('ID', 'linux'),
                           *os_release.get('ID_LIKE', '').split()]:
               print('Looks like Debian!')

       Note that the above version that uses the built-in implementation is preferred in most
       cases, and the open-coded version here is provided for reference.

NOTES