Provided by: mkosi_20.2-1_all 
NAME
mkosi — Build Bespoke OS Images
SYNOPSIS
mkosi [options...] summary
mkosi [options...] build [command line...]
mkosi [options...] shell [command line...]
mkosi [options...] boot [nspawn settings...]
mkosi [options...] qemu [qemu parameters...]
mkosi [options...] ssh [command line...]
mkosi [options...] journalctl [command line...]
mkosi [options...] coredumpctl [command line...]
mkosi [options...] clean
mkosi [options...] serve
mkosi [options...] burn <device>
mkosi [options...] bump
mkosi [options...] genkey
mkosi [options...] documentation
mkosi [options...] help
DESCRIPTION
mkosi is a tool for easily building customized OS images. It’s a fancy wrapper around dnf --installroot,
apt, pacman and zypper that may generate disk images with a number of bells and whistles.
Command Line Verbs
The following command line verbs are known:
summary
Outputs a human-readable summary of all options used for building an image. This will parse the
command line and mkosi.conf file as it would do on build, but only output what it is configured
for and not actually build anything.
build This builds the image based on the settings passed in on the command line or read from configura‐
tion files. This command is the default if no verb is explicitly specified. If any command line
arguments are specified, these are passed directly to the build script if one is defined.
shell This builds the image if it is not built yet, and then invokes systemd-nspawn to acquire an inter‐
active shell prompt in it. An optional command line may be specified after the shell verb, to be
invoked in place of the shell in the container. Use -f in order to rebuild the image uncondition‐
ally before acquiring the shell, see below. This command must be executed as root.
boot Similar to shell, but boots the image using systemd-nspawn. An optional command line may be spec‐
ified after the boot verb, which can contain extra nspawn options as well as arguments which are
passed as the kernel command line to the init system in the image.
qemu Similar to boot, but uses qemu to boot up the image, i.e. instead of container virtualization vir‐
tual machine virtualization is used. This verb is only supported for disk images that contain a
boot loader and cpio images in which a kernel was installed. For cpio images a kernel can also be
provided by passing the -kernel qemu argument to the qemu verb. Any arguments specified after the
qemu verb are appended to the qemu invocation.
ssh When the image is built with the Ssh=yes option, this command connects to a booted virtual machine
(qemu) via SSH. Make sure to run mkosi ssh with the same config as mkosi build so that it has the
necessary information available to connect to the running virtual machine via SSH. Specifically,
the SSH private key from the SshKey= setting is used to connect to the virtual machine. Use mkosi
genkey to automatically generate a key and certificate that will be picked up by mkosi. Any argu‐
ments passed after the ssh verb are passed as arguments to the ssh invocation. To connect to a
container, use machinectl login or machinectl shell.
journalctl
Uses journalctl to inspect the journal inside the image. Any arguments specified after the jour‐
nalctl verb are appended to the journalctl invocation.
coredumpctl
Uses coredumpctl to look for coredumps inside the image. Any arguments specified after the core‐
dumpctl verb are appended to the coredumpctl invocation.
clean Remove build artifacts generated on a previous build. If combined with -f, also removes incremen‐
tal build cache images. If -f is specified twice, also removes any package cache.
serve This builds the image if it is not built yet, and then serves the output directory (i.e. usually
mkosi.output/, see below) via a small embedded HTTP server, listening on port 8081. Combine with
-f in order to rebuild the image unconditionally before serving it. This command is useful for
testing network based acquisition of OS images, for example via machinectl pull-raw ... and ma‐
chinectl pull-tar ....
burn <device>
This builds the image if it is not built yet, and then writes it to the specified block device.
The partition contents are written as-is, but the GPT partition table is corrected to match sector
and disk size of the specified medium.
bump Bumps the image version from mkosi.version and writes the resulting version string to mkosi.ver‐
sion. This is useful for implementing a simple versioning scheme: each time this verb is called
the version is bumped in preparation for the subsequent build. Note that --auto-bump/-B may be
used to automatically bump the version after each successful build.
genkey Generate a pair of SecureBoot keys for usage with the SecureBootKey=/--secure-boot-key= and Se‐
cureBootCertificate=/--secure-boot-certificate= options.
documentation
Show mkosi’s documentation. By default this verb will try several ways to output the documenta‐
tion, but a specific option can be chosen with the --doc-format option. Distro packagers are en‐
couraged to add a file mkosi.1 into the mkosi/resources directory of the Python package, if it is
missing, as well as to install it in the appropriate search path for man pages. The man page can
be generated from the markdown file mkosi/resources/mkosi.md e.g via pandoc -t man -s -o mkosi.1
mkosi.md.
help This verb is equivalent to the --help switch documented below: it shows a brief usage explanation.
Commandline-only Options
Those settings cannot be configured in the configuration files.
--force, -f
Replace the output file if it already exists, when building an image. By default when building an
image and an output artifact already exists mkosi will refuse operation. Specify this option once
to delete all build artifacts from a previous run before re-building the image. If incremental
builds are enabled, specifying this option twice will ensure the intermediary cache files are re‐
moved, too, before the re-build is initiated. If a package cache is used (also see the Files sec‐
tion below), specifying this option thrice will ensure the package cache is removed too, before
the re-build is initiated. For the clean operation this option has a slightly different effect:
by default the verb will only remove build artifacts from a previous run, when specified once the
incremental cache files are deleted too, and when specified twice the package cache is also re‐
moved.
--directory=, -C
Takes a path to a directory. mkosi switches to this directory before doing anything. Note that
the various configuration files are searched for in this directory, hence using this option is an
effective way to build a project located in a specific directory.
--debug=
Enable additional debugging output.
--debug-shell=
When executing a command in the image fails, mkosi will start an interactive shell in the image
allowing further debugging.
--debug-workspace=
When an error occurs, the workspace directory will not be deleted.
--version
Show package version.
--help, -h
Show brief usage information.
--genkey-common-name=
Common name to be used when generating keys via mkosi’s genkey command. Defaults to mkosi of %u,
where %u expands to the username of the user invoking mkosi.
--genkey-valid-days=
Number of days that the keys should remain valid when generating keys via mkosi’s genkey command.
Defaults to two years (730 days).
--auto-bump=, -B
If specified, after each successful build the the version is bumped in a fashion equivalent to the
bump verb, in preparation for the next build. This is useful for simple, linear version manage‐
ment: each build in a series will have a version number one higher then the previous one.
--doc-format
The format to show the documentation in. Supports the values markdown, man, pandoc, system and
auto. In the case of markdown the documentation is shown in the original Markdown format. man
shows the documentation in man page format, if it is available. pandoc will generate the man page
format on the fly, if pandoc is available. system will show the system-wide man page for mkosi,
which may or may not correspond to the version you are using, depending on how you installed
mkosi. auto, which is the default, will try all methods in the order man, pandoc, markdown, sys‐
tem.
--json Show the summary output as JSON-SEQ.
Supported output formats
The following output formats are supported:
• Raw GPT disk image, created using systemd-repart (disk)
• Plain directory, containing the OS tree (directory)
• Tar archive (tar)
• CPIO archive (cpio)
The output format may also be set to none to have mkosi produce no image at all. This can be useful if
you only want to use the image to produce another output in the build scripts (e.g. build an rpm).
When a GPT disk image is created, repart partition definition files may be placed in mkosi.repart/ to
configure the generated disk image.
It is highly recommended to run mkosi on a file system that supports reflinks such as XFS and btrfs and
to keep all related directories on the same file system. This allows mkosi to create images very quickly
by using reflinks to perform copying via copy-on-write operations.
Configuration Settings
The following settings can be set through configuration files (the syntax with SomeSetting=value) and on
the command line (the syntax with --some-setting=value). For some command line parameters, a single-let‐
ter shortcut is also allowed. In the configuration files, the setting must be in the appropriate sec‐
tion, so the settings are grouped by section below.
Configuration is parsed in the following order:
• The command line arguments are parsed
• mkosi.local.conf is parsed if it exists. This file should be in the gitignore (or equivalent) and is
intended for local configuration.
• Any default paths (depending on the option) are configured if the corresponding path exists.
• mkosi.conf is parsed if it exists in the directory configured with --directory= or the current working
directory if --directory= is not used.
• mkosi.conf.d/ is parsed in the same directory if it exists. Each directory and each file with the
.conf extension in mkosi.conf.d/ is parsed. Any directory in mkosi.conf.d is parsed as if it were a
regular top level directory.
Note that if the same setting is configured twice, the later assignment overrides the earlier assignment
unless the setting is a list based setting. Also note that before v16, we used to do the opposite, where
the earlier assignment would be used instead of later assignments.
Settings that take a list of values are merged by appending the new values to the previously configured
values. Assigning the empty string to such a setting removes all previously assigned values, and over‐
rides any configured default values as well.
If a setting’s name in the configuration file is prefixed with @, it configures the default value used
for that setting if no explicit default value is set. This can be used to set custom default values in
configuration files that can still be overridden by specifying the setting explicitly via the CLI.
To conditionally include configuration files, the [Match] section can be used. Matches can use a pipe
symbol (|) after the equals sign (...=|...), which causes the match to become a triggering match. The
config file will be included if the logical AND of all non-triggering matches and the logical OR of all
triggering matches is satisfied. To negate the result of a match, prefix the argument with an exclama‐
tion mark. If an argument is prefixed with the pipe symbol and an exclamation mark, the pipe symbol must
be passed first, and the exclamation second.
Note that [Match] settings match against the current values of specific settings, and do not take into
account changes made to the setting in configuration files that have not been parsed yet. Also note that
matching against a setting and then changing its value afterwards in a different config file may lead to
unexpected results.
The [Match] section of a mkosi.conf file in a directory applies to the entire directory. If the condi‐
tions are not satisfied, the entire directory is skipped. The [Match] sections of files in mkosi.conf.d/
and mkosi.local.conf only apply to the file itself.
If there are multiple [Match] sections in the same configuration file, each of them has to be satisfied
in order for the configuration file to be included. Specifically, triggering matches only apply to the
current [Match] section and are reset between multiple [Match] sections. As an example, the following
will only match if the output format is one of disk or directory and the architecture is one of x86-64 or
arm64:
[Match]
Format=|disk
Format=|directory
[Match]
Architecture=|x86-64
Architecture=|arm64
Command line options that take no argument are shown without = in their long version. In the config
files, they should be specified with a boolean argument: either 1, yes, or true to enable, or 0, no,
false to disable.
[Match] Section.
Profile=
Matches against the configured profile.
Distribution=
Matches against the configured distribution.
Release=
Matches against the configured distribution release. If this condition is used and no distribu‐
tion has been explicitly configured yet, the host distribution and release are used.
Architecture=
Matches against the configured architecture. If this condition is used and no architecture has
been explicitly configured yet, the host architecture is used.
PathExists=
This condition is satisfied if the given path exists. Relative paths are interpreted relative to
the parent directory of the config file that the condition is read from.
ImageId=
Matches against the configured image ID, supporting globs. If this condition is used and no image
ID has been explicitly configured yet, this condition fails.
ImageVersion=
Matches against the configured image version. Image versions can be prepended by the operators
==, !=, >=, <=, <, > for rich version comparisons according to the UAPI group version format spec‐
ification. If no operator is prepended, the equality operator is assumed by default. If this
condition is used and no image version has been explicitly configured yet, this condition fails.
Bootable=
Matches against the configured value for the Bootable= feature. Takes a boolean value or auto.
Format=
Matches against the configured value for the Format= option. Takes an output format (see the For‐
mat= option).
SystemdVersion=
Matches against the systemd version on the host (as reported by systemctl --version). Values can
be prepended by the operators ==, !=, >=, <=, <, > for rich version comparisons according to the
UAPI group version format specification. If no operator is prepended, the equality operator is
assumed by default.
BuildSources=
Takes a build source target path (see BuildSources=). This match is satisfied if any of the con‐
figured build sources uses this target path. For example, if we have a mkosi.conf file contain‐
ing:
[Content]
BuildSources=../abc/qed:kernel
and a drop-in containing:
[Match]
BuildSources=kernel
The drop-in will be included.
Any absolute paths passed to this setting are interpreted relative to the current working directo‐
ry.
HostArchitecture=
Matches against the host’s native architecture. See the Architecture= setting for a list of pos‐
sible values.
Matcher Globs Rich Comparisons Default
────────────────────────────────────────────────────────────────────────────────
Profile= no no match fails
Distribution= no no match host distribution
Release= no no match host release
Architecture= no no match host architecture
PathExists= no no n/a
ImageId= yes no match fails
ImageVersion= no yes match fails
Bootable= no no match auto feature
Format= no no match default format
SystemdVersion= no yes n/a
BuildSources= no no match fails
HostArchitecture= no no n/a
[Config] Section
Profile=, --profile=
Select the given profile. A profile is a configuration file or directory in the mkosi.profiles/
directory. When selected, this configuration file or directory is included after parsing the
mkosi.conf file, but before any mkosi.conf.d/*.conf drop in configuration.
Include=, --include=
Include extra configuration from the given file or directory. The extra configuration is included
immediately after parsing the setting, except when a default is set using @Include=, in which case
the configuration is included after parsing all the other configuration files. Note that each
path containing extra configuration is only parsed once, even if included more than once with In‐
clude=.
InitrdInclude=, --initrd-include=
Same as Include=, but the extra configuration files or directories are included when building the
default initrd.
Images=, --image=
If specified, only build the given image. Can be specified multiple times to build multiple im‐
ages. All the given images and their dependencies are built. If not specified, all images are
built. See the Building multiple images section for more information. Note that this section on‐
ly takes effect when specified in the global configuration files. It has no effect if specified
as an image specific setting.
Dependencies=, --dependency=
The images that this image depends on specified as a comma-separated list. All images configured
in this option will be built before this image and will be pulled in as dependencies of this image
when Images= is used.
MinimumVersion=, --minimum-version=
The minimum mkosi version required to build this configuration. If specified multiple times, the
highest specified version is used.
[Distribution] Section
Distribution=, --distribution=, -d
The distribution to install in the image. Takes one of the following arguments: fedora, debian,
ubuntu, arch, opensuse, mageia, centos, rhel, rhel-ubi, openmandriva, rocky, alma, custom. If not
specified, defaults to the distribution of the host or custom if the distribution of the host is
not a supported distribution.
Release=, --release=, -r
The release of the distribution to install in the image. The precise syntax of the argument this
takes depends on the distribution used, and is either a numeric string (in case of Fedora Linux,
CentOS, ..., e.g. 29), or a distribution version name (in case of Debian, Ubuntu, ..., e.g. art‐
ful). Defaults to a recent version of the chosen distribution, or the version of the distribution
running on the host if it matches the configured distribution.
Architecture=, --architecture=
The architecture to build the image for. The architectures that are actually supported depends on
the distribution used and whether a bootable image is requested or not. When building for a for‐
eign architecture, you’ll also need to install and register a user mode emulator for that archi‐
tecture. One of the following architectures can be specified per image built: alpha, arc, arm,
arm64, ia64, loongarch64, mips64-le, mips-le, parisc, ppc, ppc64, ppc64-le, riscv32, riscv64,
s390, s390x, tilegx, x86, x86-64.
Mirror=, --mirror=, -m
The mirror to use for downloading the distribution packages. Expects a mirror URL as argument.
If not provided, the default mirror for the distribution is used. The default mirrors for each
distribution are as follows (unless specified, the same mirror is used for all architectures):
x86-64 aarch64
─────────────────────────────────────────────────────────────────────────────
debian http://deb.debian.org/debian
arch https://geo.mirror.pkg‐ http://mirror.archlin‐
build.com uxarm.org
opensuse http://download.opensuse.org
ubuntu http://archive.ubuntu.com http://ports.ubuntu.com
centos https://mirrors.centos.org
rocky https://mirrors.rockylin‐
ux.org
alma https://mirrors.almalinux.org
fedora https://mirrors.fedorapro‐
ject.org
rhel-ubi https://cdn-ubi.redhat.com
mageia https://www.mageia.org
openmandriva http://mirrors.openmandri‐
va.org
LocalMirror=, --local-mirror=
The mirror will be used as a local, plain and direct mirror instead of using it as a prefix for
the full set of repositories normally supported by distributions. Useful for fully offline builds
with a single repository. Supported on deb/rpm/arch based distributions. Overrides --mirror= but
only for the local mkosi build, it will not be configured inside the final image, --mirror= (or
the default repository) will be configured inside the final image instead.
RepositoryKeyCheck=, --repository-key-check=
Controls signature/key checks when using repositories, enabled by default. Useful to disable
checks when combined with --local-mirror= and using only a repository from a local filesystem.
Not used for DNF-based distros yet.
Repositories=, --repositories=
Enable package repositories that are disabled by default. This can be used to enable the EPEL re‐
pos for CentOS or different components of the Debian/Ubuntu repositories.
CacheOnly=, --cache-only=
If specified, the package manager is instructed not to contact the network for updating package
data. This provides a minimal level of reproducibility, as long as the package cache is already
fully populated.
PackageManagerTrees=, --package-manager-tree=
This option mirrors the above SkeletonTrees= option and defaults to the same value if not config‐
ured otherwise, but installs the files to a subdirectory of the workspace directory instead of the
OS tree. This subdirectory of the workspace is used to configure the package manager. mkosi will
look for the package manager configuration and related files in the configured package manager
trees. Unless specified otherwise, it will use the configuration files from their canonical loca‐
tions in /usr or /etc in the package manager trees. For example, it will look for
etc/dnf/dnf.conf in the package manager trees if dnf is used to install packages. SkeletonTrees=
and PackageManagerTrees= fulfill similar roles. Use SkeletonTrees= if you want the files to be
present in the final image. Use PackageManagerTrees= if you don’t want the files to be present in
the final image, e.g. when building an initrd or if you want to refer to paths outside of the im‐
age in your repository configuration.
[Output] Section
Format=, --format=, -t
The image format type to generate. One of directory (for generating an OS image directly in a lo‐
cal directory), tar (similar, but a tarball of the OS image is generated), cpio (similar, but a
cpio archive is generated), disk (a block device OS image with a GPT partition table), uki (a uni‐
fied kernel image with the OS image in the .initrd PE section), esp (uki but wrapped in a disk im‐
age with only an ESP partition), sysext, confext, portable or none (the OS image is solely intend‐
ed as a build image to produce another artifact). If the disk output format is used, the disk im‐
age is generated using systemd-repart. The repart partition definition files to use can be con‐
figured using the RepartDirectories= setting or via mkosi.repart/. When verity partitions are
configured using systemd-repart’s Verity= setting, mkosi will automatically parse the verity hash
partition’s roothash from systemd-repart’s JSON output and include it in the kernel command line
of every unified kernel image built by mkosi.
ManifestFormat=, --manifest-format=
The manifest format type or types to generate. A comma-delimited list consisting of json (the
standard JSON output format that describes the packages installed), changelog (a human-readable
text format designed for diffing). By default no manifest is generated.
Output=, --output=, -o
Name to use for the generated output image file or directory. All outputs will be prefixed with
the given name. Defaults to image or, if ImageId= is specified, it is used as the default output
name, optionally suffixed with the version set with ImageVersion=. Note that this option does not
allow configuring the output directory, use OutputDirectory= for that. Note that this only speci‐
fies the output prefix, depending on the specific output format, compression and image version
used, the full output name might be image_7.8.raw.xz.
CompressOutput=, --compress-output=
Configure compression for the resulting image or archive. The argument can be either a boolean or
a compression algorithm (xz, zstd). zstd compression is used by default, except CentOS and deriv‐
atives up to version 8, which default to xz. Note that when applied to block device image types,
compression means the image cannot be started directly but needs to be decompressed first. This
also means that the shell, boot, qemu verbs are not available when this option is used. Implied
for tar, cpio, uki, and esp.
OutputDirectory=, --output-dir=, -O
Path to a directory where to place all generated artifacts. If this is not specified and the di‐
rectory mkosi.output/ exists in the local directory, it is automatically used for this purpose.
WorkspaceDirectory=, --workspace-dir=
Path to a directory where to store data required temporarily while building the image. This di‐
rectory should have enough space to store the full OS image, though in most modes the actually
used disk space is smaller. If not specified, a subdirectory of $XDG_CACHE_HOME (if set),
$HOME/.cache (if set) or /var/tmp is used. The data in this directory is removed automatically
after each build. It’s safe to manually remove the contents of this directory should an mkosi in‐
vocation be aborted abnormally (for example, due to reboot/power failure).
CacheDirectory=, --cache-dir=
Takes a path to a directory to use as package cache for the distribution package manager used. If
this option is not used, but a mkosi.cache/ directory is found in the local directory it is auto‐
matically used for this purpose.
BuildDirectory=, --build-dir=
Takes a path to a directory to use as the build directory for build systems that support out-of-
tree builds (such as Meson). The directory used this way is shared between repeated builds, and
allows the build system to reuse artifacts (such as object files, executable, ...) generated on
previous invocations. The build scripts can find the path to this directory in the $BUILDDIR en‐
vironment variable. This directory is mounted into the image’s root directory when mkosi-chroot
is invoked during execution of the build scripts. If this option is not specified, but a directo‐
ry mkosi.builddir/ exists in the local directory it is automatically used for this purpose (also
see the Files section below).
ImageVersion=, --image-version=
Configure the image version. This accepts any string, but it is recommended to specify a series
of dot separated components. The version may also be configured in a file mkosi.version in which
case it may be conveniently managed via the bump verb or the --auto-bump option. When specified
the image version is included in the default output file name, i.e. instead of image.raw the de‐
fault will be image_0.1.raw for version 0.1 of the image, and similar. The version is also passed
via the $IMAGE_VERSION to any build scripts invoked (which may be useful to patch it into /etc/os-
release or similar, in particular the IMAGE_VERSION= field of it).
ImageId=, --image-id=
Configure the image identifier. This accepts a freeform string that shall be used to identify the
image with. If set the default output file will be named after it (possibly suffixed with the
version). The identifier is also passed via the $IMAGE_ID to any build scripts invoked. The im‐
age ID is automatically added to /usr/lib/os-release.
SplitArtifacts=, --split-artifacts
If specified and building a disk image, pass --split=yes to systemd-repart to have it write out
split partition files for each configured partition. Read the man (https://www.freedesk‐
top.org/software/systemd/man/systemd-repart.html#--split=BOOL) page for more information. This is
useful in A/B update scenarios where an existing disk image shall be augmented with a new version
of a root or /usr partition along with its Verity partition and unified kernel.
RepartDirectories=, --repart-dir=
Paths to directories containing systemd-repart partition definition files that are used when mkosi
invokes systemd-repart when building a disk image. If mkosi.repart/ exists in the local directo‐
ry, it will be used for this purpose as well. Note that mkosi invokes repart with --root= set to
the root of the image root, so any CopyFiles= source paths in partition definition files will be
relative to the image root directory.
SectorSize=, --sector-size=
Override the default sector size that systemd-repart uses when building a disk image.
RepartOffline=, --repart-offline=
Specifies whether to build disk images using loopback devices. Enabled by default. When enabled,
systemd-repart will not use loopback devices to build disk images. When disabled, systemd-repart
will always use loopback devices to build disk images. Note that when using RepartOffline=no
mkosi cannot run unprivileged and the image build has to be done as the root user outside of any
containers and with loopback devices available on the host system. There are currently two known
scenarios where RepartOffline=no has to be used. The first is when using Subvolumes= in a repart
partition definition file, as subvolumes cannot be created without using loopback devices. The
second is when creating a system with SELinux and an XFS root partition. Because mkfs.xfs does
not support populating an XFS filesystem with extended attributes, loopback devices have to be
used to ensure the SELinux extended attributes end up in the generated XFS filesystem.
Overlay=, --overlay
When used together with BaseTrees=, the output will consist only out of changes to the specified
base trees. Each base tree is attached as a lower layer in an overlayfs structure, and the output
becomes the upper layer, initially empty. Thus files that are not modified compared to the base
trees will not be present in the final output. This option may be used to create systemd system
extensions or portable services (https://uapi-group.org/specifications/specs/extension_image).
UseSubvolumes=, --use-subvolumes=
Takes a boolean or auto. Enables or disables use of btrfs subvolumes for directory tree outputs.
If enabled, mkosi will create the root directory as a btrfs subvolume and use btrfs subvolume
snapshots where possible to copy base or cached trees which is much faster than doing a recursive
copy. If explicitly enabled and btrfs is not installed or subvolumes cannot be created, an error
is raised. If auto, missing btrfs or failures to create subvolumes are ignored.
Seed=, --seed=
Takes a UUID as argument or the special value random. Overrides the seed that systemd-repart(8)
(https://www.freedesktop.org/software/systemd/man/systemd-repart.service.html) uses when building
a disk image. This is useful to achieve reproducible builds, where deterministic UUIDs and other
partition metadata should be derived on each build.
SourceDateEpoch=, --source-date-epoch=
Takes a timestamp as argument. Resets file modification times of all files to this timestamp.
The variable is also propagated to systemd-repart and scripts executed by mkosi. If not set ex‐
plicitly, SOURCE_DATE_EPOCH from --environment and from the host environment are tried in that or‐
der. This is useful to make builds reproducible. See SOURCE_DATE_EPOCH (https://reproducible-
builds.org/specs/source-date-epoch/) for more information.
[Content] Section
Packages=, --package=, -p
Install the specified distribution packages (i.e. RPM, DEB, ...) in the image. Takes a comma
separated list of package specifications. This option may be used multiple times in which case
the specified package lists are combined. Use BuildPackages= to specify packages that shall only
be installed in an overlay that is mounted when the prepare scripts are executed with the build
argument and when the build scripts are executed. The types and syntax of package specifications
that are allowed depend on the package installer (e.g. dnf for rpm-based distros or apt for deb-
based distros), but may include package names, package names with version and/or architecture,
package name globs, paths to packages in the file system, package groups, and virtual provides,
including file paths. Example: when using a distro that uses dnf, the following configuration
would install the meson package (in the latest version), the 32-bit version of the libfdisk-devel
package, all available packages that start with the git- prefix, a systemd rpm from the local file
system, one of the packages that provides /usr/bin/ld, the packages in the Development Tools
group, and the package that contains the mypy python module.
Packages=meson
libfdisk-devel.i686
git-*
prebuilt/rpms/systemd-249-rc1.local.rpm
/usr/bin/ld
@development-tools
python3dist(mypy)
: Note that since mkosi runs in a sandbox with most of the host files unavailable, any local packages
have to be mounted into the sandbox explicitly using BuildSources=. For example, let’s say we have a lo‐
cal package located at ../my-packages/abc.rpm relative to the mkosi working directory, then we’d be able
to install it as follows:
BuildSources=../my-packages:my-packages-in-sandbox
Packages=my-packages-in-sandbox/abc.rpm
BuildPackages=, --build-package=
Similar to Packages=, but configures packages to install only in an overlay that is made available
on top of the image to the prepare scripts when executed with the build argument and the build
scripts. This option should be used to list packages containing header files, compilers, build
systems, linkers and other build tools the mkosi.build scripts require to operate. Note that
packages listed here will be absent in the final image.
PackageDirectories=, --package-directory=
Specify directories containing extra packages to be made available during the build. mkosi will
create a local repository containing all packages in these directories and make it available when
installing packages or running scripts. Note that this local repository is also made available
when running scripts. Build scripts can add more packages to the local repository by placing the
built packages in $PACKAGEDIR.
WithRecommends=, --with-recommends=
Configures whether to install recommended or weak dependencies, depending on how they are named by
the used package manager, or not. By default, recommended packages are not installed. This is
only used for package managers that support the concept, which are currently apt, dnf and zypper.
WithDocs=, --with-docs
Include documentation in the image. Enabled by default. When disabled, if the underlying distri‐
bution package manager supports it documentation is not included in the image. The $WITH_DOCS en‐
vironment variable passed to the mkosi.build scripts is set to 0 or 1 depending on whether this
option is enabled or disabled.
BaseTrees=, --base-tree=
Takes a comma separated list of paths to use as base trees. When used, these base trees are each
copied into the OS tree and form the base distribution instead of installing the distribution from
scratch. Only extra packages are installed on top of the ones already installed in the base
trees. Note that for this to work properly, the base image still needs to contain the package
manager metadata (see CleanPackageMetadata=). Instead of a directory, a tar file or a disk image
may be provided. In this case it is unpacked into the OS tree. This mode of operation allows
setting permissions and file ownership explicitly, in particular for projects stored in a version
control system such as git which retain full file ownership and access mode metadata for committed
files.
SkeletonTrees=, --skeleton-tree=
Takes a comma separated list of colon separated path pairs. The first path of each pair refers to
a directory to copy into the OS tree before invoking the package manager. The second path of each
pair refers to the target directory inside the image. If the second path is not provided, the di‐
rectory is copied on top of the root directory of the image. The second path is always interpret‐
ed as an absolute path. Use this to insert files and directories into the OS tree before the
package manager installs any packages. If the mkosi.skeleton/ directory is found in the local di‐
rectory it is also used for this purpose with the root directory as target (also see the Files
section below). Note that skeleton trees are cached and any changes to skeleton trees after a
cached image has been built (when using Incremental=) are only applied when the cached image is
rebuilt (by using -ff or running mkosi -f clean). As with the base tree logic above, instead of a
directory, a tar file may be provided too. mkosi.skeleton.tar will be automatically used if found
in the local directory.
ExtraTrees=, --extra-tree=
Takes a comma separated list of colon separated path pairs. The first path of each pair refers to
a directory to copy from the host into the image. The second path of each pair refers to the tar‐
get directory inside the image. If the second path is not provided, the directory is copied on
top of the root directory of the image. The second path is always interpreted as an absolute
path. Use this to override any default configuration files shipped with the distribution. If the
mkosi.extra/ directory is found in the local directory it is also used for this purpose with the
root directory as target. (also see the Files section below). As with the base tree logic above,
instead of a directory, a tar file may be provided too. mkosi.extra.tar will be automatically
used if found in the local directory.
RemovePackages=, --remove-package=
Takes a comma-separated list of package specifications for removal, in the same format as Pack‐
ages=. The removal will be performed as one of the last steps. This step is skipped if Clean‐
PackageMetadata=no is used.
RemoveFiles=, --remove-files=
Takes a comma-separated list of globs. Files in the image matching the globs will be purged at
the end.
CleanPackageMetadata=, --clean-package-metadata=
Enable/disable removal of package manager databases at the end of installation. Can be specified
as true, false, or auto (the default). With auto, files will be removed if the respective package
manager executable is not present at the end of the installation.
PrepareScripts=, --prepare-script=
Takes a comma-separated list of paths to executables that are used as the prepare scripts for this
image. See the Scripts section for more information.
BuildScripts=, --build-script=
Takes a comma-separated list of paths to executables that are used as the build scripts for this
image. See the Scripts section for more information.
PostInstallationScripts=, --postinst-script=
Takes a comma-separated list of paths to executables that are used as the post-installation
scripts for this image. See the Scripts section for more information.
FinalizeScripts=, --finalize-script=
Takes a comma-separated list of paths to executables that are used as the finalize scripts for
this image. See the Scripts section for more information.
BuildSources=, --build-sources=
Takes a comma separated list of colon separated path pairs. The first path of each pair refers to
a directory to mount from the host. The second path of each pair refers to the directory where
the source directory should be mounted when running scripts. Every target path is prefixed with
/work/src and all build sources are sorted lexicographically by their target before mounting, so
that top level paths are mounted first. If not configured explicitly, the current working direc‐
tory is mounted to /work/src.
BuildSourcesEphemeral=, --build-sources-ephemeral=
Takes a boolean. Disabled by default. Configures whether changes to source directories (The
working directory and configured using BuildSources=) are persisted. If enabled, all source di‐
rectories will be reset to their original state after scripts finish executing.
Environment=, --environment=
Adds variables to the environment that package managers and the prepare/build/postinstall/finalize
scripts are executed with. Takes a space-separated list of variable assignments or just variable
names. In the latter case, the values of those variables will be passed through from the environ‐
ment in which mkosi was invoked. This option may be specified more than once, in which case all
listed variables will be set. If the same variable is set twice, the later setting overrides the
earlier one.
EnvironmentFiles=, --env-file=
Takes a comma-separated list of paths to files that contain environment variable definitions to be
added to the scripting environment. Uses mkosi.env if it is found in the local directory. The
variables are first read from mkosi.env if it exists, then from the given list of files and then
from the Environment= settings.
WithTests=, --without-tests, -T
If set to false (or when the command-line option is used), the $WITH_TESTS environment variable is
set to 0 when the mkosi.build scripts are invoked. This is supposed to be used by the build
scripts to bypass any unit or integration tests that are normally run during the source build
process. Note that this option has no effect unless the mkosi.build build scripts honor it.
WithNetwork=, --with-network=
When true, enables network connectivity while the build scripts mkosi.build are invoked. By de‐
fault, the build scripts run with networking turned off. The $WITH_NETWORK environment variable
is passed to the mkosi.build build scripts indicating whether the build is done with or without
network.
Bootable=, --bootable=
Takes a boolean or auto. Enables or disables generation of a bootable image. If enabled, mkosi
will install an EFI bootloader, and add an ESP partition when the disk image output is used. If
the selected EFI bootloader (See Bootloader=) is not installed or no kernel images can be found,
the build will fail. auto behaves as if the option was enabled, but the build won’t fail if ei‐
ther no kernel images or the selected EFI bootloader can’t be found. If disabled, no bootloader
will be installed even if found inside the image, no unified kernel images will be generated and
no ESP partition will be added to the image if the disk output format is used.
Bootloader=, --bootloader=
Takes one of none, systemd-boot, uki or grub. Defaults to systemd-boot. If set to none, no EFI
bootloader will be installed into the image. If set to systemd-boot, systemd-boot will be in‐
stalled and for each installed kernel, a UKI will be generated and stored in EFI/Linux in the ESP.
If set to uki, a single UKI will be generated for the latest installed kernel (the one with the
highest version) which is installed to EFI/BOOT/BOOTX64.EFI in the ESP. If set to grub, for each
installed kernel, a UKI will be generated and stored in EFI/Linux in the ESP. For each generated
UKI, a menu entry is appended to the grub configuration in grub/grub.cfg in the ESP which chain‐
loads into the UKI. A shim grub.cfg is also written to EFI/<distribution>/grub.cfg in the ESP
which loads grub/grub.cfg in the ESP for compatibility with signed versions of grub which load the
grub configuration from this location. Note that we do not yet install grub to the ESP when Boot‐
loader= is set to grub. This has to be done manually in a postinst or finalize script. The grub
EFI binary should be installed to /efi/EFI/BOOT/BOOTX64.EFI (or similar depending on the architec‐
ture) and should be configured to load its configuration from EFI/<distribution>/grub.cfg in the
ESP. Signed versions of grub shipped by distributions will load their configuration from this lo‐
cation by default.
BiosBootloader=, --bios-bootloader=
Takes one of none or grub. Defaults to none. If set to none, no BIOS bootloader will be in‐
stalled. If set to grub, grub is installed as the BIOS boot loader if a bootable image is re‐
quested with the Bootable= option. If no repart partition definition files are configured, mkosi
will add a grub BIOS boot partition and an EFI system partition to the default partition defini‐
tion files. Note that this option is not mutually exclusive with Bootloader=. It is possible to
have an image that is both bootable on UEFI and BIOS by configuring both Bootloader= and BiosBoot‐
loader=. The grub BIOS boot partition should have UUID 21686148-6449-6e6f-744e-656564454649 and
should be at least 1MB. Even if no EFI bootloader is installed, we still need an ESP for BIOS
boot as that’s where we store the kernel, initrd and grub modules.
ShimBootloader=, --shim-bootloader=
Takes one of none, unsigned, or signed. Defaults to none. If set to none, shim and MokManager
will not be installed to the ESP. If set to unsigned, mkosi will search for unsigned shim and
MokManager EFI binaries and install them. If SecureBoot= is enabled, mkosi will sign the unsigned
EFI binaries before installing thel. If set to signed, mkosi will search for signed EFI binaries
and install those. Even if SecureBoot= is enabled, mkosi won’t sign these binaries again. Note
that this option only takes effect when an image that is bootable on UEFI firmware is requested
using other options (Bootable=, Bootloader=).
Initrds=, --initrd
Use user-provided initrd(s). Takes a comma separated list of paths to initrd files. This option
may be used multiple times in which case the initrd lists are combined. If no initrds are speci‐
fied and a bootable image is requested, mkosi will automatically build a default initrd.
InitrdPackages=, --initrd-package=
Extra packages to install into the default initrd. Takes a comma separated list of package speci‐
fications. This option may be used multiple times in which case the specified package lists are
combined.
KernelCommandLine=, --kernel-command-line=
Use the specified kernel command line when building images.
KernelModulesInclude=, --kernel-modules-include=
Takes a list of regex patterns that specify kernel modules to include in the image. Patterns
should be relative to the /usr/lib/modules/<kver>/kernel directory. mkosi checks for a match any‐
where in the module path (e.g. i915 will match against drivers/gpu/drm/i915.ko). All modules that
match any of the specified patterns are included in the image. All module and firmware dependen‐
cies of the matched modules are included in the image as well. This setting takes priority over
KernelModulesExclude= and only makes sense when used in combination with it because all kernel
modules are included in the image by default.
KernelModulesExclude=, --kernel-modules-exclude=
Takes a list of regex patterns that specify modules to exclude from the image. Behaves the same
as KernelModulesInclude= except that all modules that match any of the specified patterns are ex‐
cluded from the image.
KernelModulesIncludeHost=, --kernel-modules-include-host=
Takes a boolean. Specifies whether to include the currently loaded modules on the host system in
the image. This setting takes priority over KernelModulesExclude= and only makes sense when used
in combination with it because all kernel modules are included in the image by default.
KernelModulesInitrd=, --kernel-modules-initrd=
Enable/Disable generation of the kernel modules initrd when building a bootable image. Enabled by
default. If enabled, when building a bootable image, for each kernel that we assemble a unified
kernel image for we generate an extra initrd containing only the kernel modules for that kernel
version and append it to the prebuilt initrd. This allows generating kernel independent initrds
which are augmented with the necessary kernel modules when the UKI is assembled.
KernelModulesInitrdInclude=, --kernel-modules-initrd-include=
Like KernelModulesInclude=, but applies to the kernel modules included in the kernel modules ini‐
trd.
KernelModulesInitrdExclude=, --kernel-modules-initrd-exclude=
Like KernelModulesExclude=, but applies to the kernel modules included in the kernel modules ini‐
trd.
KernelModulesInitrdIncludeHost=, --kernel-modules-initrd-include-host=
Like KernelModulesIncludeHost=, but applies to the kernel modules included in the kernel modules
initrd.
Locale=, --locale=, LocaleMessages=, --locale-messages=, Keymap=, --keymap=, Timezone=, --timezone=,
Hostname=, --hostname=, RootShell=, --root-shell=
The settings Locale=, --locale=, LocaleMessages=, --locale-messages=, Keymap=, --keymap=, Time‐
zone=, --timezone=, Hostname=, --hostname=, RootShell=, --root-shell= correspond to the identical‐
ly named systemd-firstboot options. See the systemd firstboot manpage (https://www.freedesk‐
top.org/software/systemd/man/systemd-firstboot.html) for more information. Additionally, where
applicable, the corresponding systemd credentials for these settings are written to /usr/lib/cred‐
store, so that they apply even if only /usr is shipped in the image.
RootPassword=, --root-password=,
Set the system root password. If this option is not used, but a mkosi.rootpw file is found in the
local directory, the password is automatically read from it. If the password starts with hashed:,
it is treated as an already hashed root password. The root password is also stored in
/usr/lib/credstore under the appropriate systemd credential so that it applies even if only /usr
is shipped in the image. To create an unlocked account without any password use hashed: without a
hash.
Autologin=, --autologin
Enable autologin for the root user on /dev/pts/0 (nspawn), /dev/tty1 and /dev/ttyS0.
MakeInitrd=, --make-initrd
Add /etc/initrd-release and /init to the image so that it can be used as an initramfs.
Ssh=, --ssh
If specified, an sshd socket unit and matching service are installed in the final image that ex‐
pose SSH over VSock. When building with this option and running the image using mkosi qemu, the
mkosi ssh command can be used to connect to the container/VM via SSH. Note that you still have to
make sure openssh is installed in the image to make this option behave correctly. Run mkosi
genkey to automatically generate an X509 certificate and private key to be used by mkosi to enable
SSH access to any virtual machines via mkosi ssh. To access images booted using mkosi boot, use
machinectl.
SELinuxRelabel=, --selinux-relabel=
Specifies whether to relabel files to match the image’s SELinux policy. Takes a boolean value or
auto. Defaults to auto. If disabled, files will not relabeled. If enabled, an SELinux policy
has to be installed in the image and setfiles has to be available to relabel files. If any errors
occur during setfiles, the build will fail. If set to auto, files will be relabeled if an SELinux
policy is installed in the image and if setfiles is available. Any errors occurred during set‐
files will be ignored. Note that when running unprivileged, setfiles will fail to set any labels
that are not in the host’s SELinux policy. To ensure setfiles succeeds without errors, make sure
to run mkosi as root or build from a host system with the same SELinux policy as the image you’re
building.
[Validation] Section
SecureBoot=, --secure-boot
Sign systemd-boot (if it is not signed yet) and any generated unified kernel images for UEFI Se‐
cureBoot.
SecureBootAutoEnroll=, --secure-boot-auto-enroll=
Set up automatic enrollment of the secure boot keys in virtual machines as documented in the sys‐
temd-boot man page (https://www.freedesktop.org/software/systemd/man/systemd-boot.html) if Secure‐
Boot= is used. Note that systemd-boot will only do automatic secure boot key enrollment in virtu‐
al machines starting from systemd v253. To do auto enrollment on systemd v252 or on bare metal
machines, write a systemd-boot configuration file to /efi/loader/loader.conf using an extra tree
with secure-boot-enroll force or secure-boot-enroll manual in it. Auto enrollment is not support‐
ed on systemd versions older than v252. Defaults to yes.
SecureBootKey=, --secure-boot-key=
Path to the PEM file containing the secret key for signing the UEFI kernel image, if SecureBoot=
is used.
SecureBootCertificate=, --secure-boot-certificate=
Path to the X.509 file containing the certificate for the signed UEFI kernel image, if SecureBoot=
is used.
SecureBootSignTool=, --secure-boot-sign-tool
Tool to use to sign secure boot PE binaries. Takes one of sbsign, pesign or auto. Defaults to
auto. If set to auto, either sbsign or pesign are used if available, with sbsign being preferred
if both are installed.
VerityKey=, --verity-key=
Path to the PEM file containing the secret key for signing the verity signature, if a verity sig‐
nature partition is added with systemd-repart.
VerityCertificate=, --verity-certificate=
Path to the X.509 file containing the certificate for signing the verity signature, if a verity
signature partition is added with systemd-repart.
SignExpectedPcr=, --sign-expected-pcr
Measure the components of the unified kernel image (UKI) using systemd-measure and embed the PCR
signature into the unified kernel image. This option takes a boolean value or the special value
auto, which is the default, which is equal to a true value if the systemd-measure binary is in
PATH.
Passphrase=, --passphrase
Specify the path to a file containing the passphrase to use for LUKS encryption. It should con‐
tain the passphrase literally, and not end in a newline character (i.e. in the same format as
cryptsetup and /etc/crypttab expect the passphrase files). The file must have an access mode of
0600 or less.
Checksum=, --checksum
Generate a SHA256SUMS file of all generated artifacts after the build is complete.
Sign=, --sign
Sign the generated SHA256SUMS using gpg after completion.
Key=, --key=
Select the gpg key to use for signing SHA256SUMS. This key must be already present in the gpg
keyring.
[Host] Section
Incremental=, --incremental=, -i
Enable incremental build mode. In this mode, a copy of the OS image is created immediately after
all OS packages are installed and the prepare scripts have executed but before the mkosi.build
scripts are invoked (or anything that happens after it). On subsequent invocations of mkosi with
the -i switch this cached image may be used to skip the OS package installation, thus drastically
speeding up repetitive build times. Note that while there is some rudimentary cache invalidation,
it is definitely not perfect. In order to force rebuilding of the cached image, combine -i with
-ff to ensure the cached image is first removed and then re-created.
NSpawnSettings=, --settings=
Specifies a .nspawn settings file for systemd-nspawn to use in the boot and shell verbs, and to
place next to the generated image file. This is useful to configure the systemd-nspawn environ‐
ment when the image is run. If this setting is not used but an mkosi.nspawn file found in the lo‐
cal directory it is automatically used for this purpose.
ExtraSearchPaths=, --extra-search-path=
List of colon-separated paths to look for tools in, before using the regular $PATH search path.
QemuGui=, --qemu-gui=
If enabled, qemu is executed with its graphical interface instead of with a serial console.
QemuSmp=, --qemu-smp=
When used with the qemu verb, this options sets qemu’s -smp argument which controls the number of
guest’s CPUs. Defaults to 2.
QemuMem=, --qemu-mem=
When used with the qemu verb, this options sets qemu’s -m argument which controls the amount of
guest’s RAM. Defaults to 2G.
QemuKvm=, --qemu-kvm=
When used with the qemu verb, this option specifies whether QEMU should use KVM acceleration.
Takes a boolean value or auto. Defaults to auto.
QemuVsock=, --qemu-vsock=
When used with the qemu verb, this option specifies whether QEMU should be configured with a
vsock. Takes a boolean value or auto. Defaults to auto.
QemuVsockConnectionId=, --qemu-vsock-cid=
When used with the qemu verb, this option specifies the vsock connection ID to use. Takes a num‐
ber in the interval [3, 0xFFFFFFFF) or hash or auto. Defaults to hash. When set to hash, the
connection ID will be derived from the full path to the image. When set to auto, mkosi will try
to find a free connection ID automatically. Otherwise, the provided number will be used as is.
Note that when set to auto, mkosi ssh cannot be used as we cannot figure out which free connection
ID we found when booting the image earlier.
QemuSwtpm=, --qemu-swtpm=
When used with the qemu verb, this option specifies whether to start an instance of swtpm to be
used as a TPM with qemu. This requires swtpm to be installed on the host. Takes a boolean value
or auto. Defaults to auto.
QemuCdrom=, --qemu-cdrom=
When used with the qemu verb, this option specifies whether to attach the image to the virtual ma‐
chine as a CD-ROM device. Takes a boolean. Defaults to no.
QemuFirmware=, --qemu-firmware=
When used with the qemu verb, this option specifies which firmware to use. Takes one of uefi,
bios, linux, or auto. Defaults to auto. When set to uefi, the OVMF firmware is used. When set
to bios, the default SeaBIOS firmware is used. When set to linux, direct kernel boot is used.
See the QemuKernel= option for more details on which kernel image is used with direct kernel boot.
When set to auto, linux is used if a cpio image is being booted, uefi otherwise.
QemuFirmwareVariables=, --qemu-firmware-variables=
When used with the qemu verb, this option specifies the path to the the firmware variables file to
use. Currently, this option is only taken into account when the uefi firmware is used. If not
specified, mkosi will search for the default variables file and use that instead. virt-fw-vars
from the virt-firmware (https://gitlab.com/kraxel/virt-firmware) project can be used to customize
OVMF variable files. Some distributions also provide variable files which already have Mi‐
crosoft’s certificates for secure boot enrolled. For Fedora and Debian these are OVMF_VARS.sec‐
boot.fd and OVMF_VARS_4M.ms.fd under /usr/share/OVMF respectively. You can use locate and look
under /usr/share/qemu/firmware for hints on where to find these files if your distribution ships
them.
QemuKernel=, --qemu-kernel=
Set the kernel image to use for qemu direct kernel boot. If not specified, mkosi will use the
kernel provided via the command line (-kernel option) or latest the kernel that was installed into
the image (or fail if no kernel was installed into the image). Note that when the cpio output
format is used, direct kernel boot is used regardless of the configured firmware. Depending on
the configured firmware, qemu might boot the kernel itself or using the configured firmware.
QemuDrives=, --qemu-drive=
Add a qemu drive. Takes a colon-delimited string of format <id>:<size>[:<directory>[:<options>]].
id specifies the qemu id we assign to the drive. This can be used as the drive= property in vari‐
ous qemu devices. size specifies the size of the drive. This takes a size in bytes. Additional‐
ly, the suffixes K, M and G can be used to specify a size in kilobytes, megabytes and gigabytes
respectively. directory optionally specifies the directory in which to create the file backing
the drive. options optionally specifies extra comma-delimited properties which are passed verba‐
time to qemu’s -drive option.
QemuArgs=
Space-delimited list of additional arguments to pass when invoking qemu.
Ephemeral=, --ephemeral
When used with the shell, boot, or qemu verbs, this option runs the specified verb on a temporary
snapshot of the output image that is removed immediately when the container terminates. Taking
the temporary snapshot is more efficient on file systems that support reflinks natively (btrfs or
xfs) than on more traditional file systems that do not (ext4).
Credentials=, --credential=
Set credentials to be passed to systemd-nspawn or qemu respectively when mkosi shell/boot or mkosi
qemu are used. This option takes a space separated list of key=value assignments.
KernelCommandLineExtra=, --kernel-command-line-extra=
Set extra kernel command line entries that are appended to the kernel command line at runtime when
booting the image. When booting in a container, these are passed as extra arguments to systemd.
When booting in a VM, these are appended to the kernel command line via the SMBIOS io.sys‐
temd.stub.kernel-cmdline-extra OEM string. This will only be picked up by systemd-boot/systemd-
stub versions newer than or equal to v254.
Acl=, --acl=
If specified, ACLs will be set on any generated root filesystem directories that allow the user
running mkosi to remove them without needing privileges.
ToolsTree=, --tools-tree=
If specified, programs executed by mkosi are looked up inside the given tree instead of in the
host system. Use this option to make image builds more reproducible by always using the same ver‐
sions of programs to build the final image instead of whatever version is installed on the host
system. If this option is not used, but the mkosi.tools/ directory is found in the local directo‐
ry it is automatically used for this purpose with the root directory as target. Note that when
looking up binaries in --tools-tree=, only /usr/bin and /usr/sbin are considered. Specifically,
paths specified by --extra-search-path= are ignored when looking up binaries in the given tools
tree. If set to default, mkosi will automatically add an extra tools tree image and use it as the
tools tree. The following table shows for which distributions default tools tree packages are de‐
fined and which packages are included in those default tools trees:
Fedora CentOS Debian Ubuntu Arch openSUSE
─────────────────────────────────────────────────────────────────────────────────────────
apt X X X X X
archlinux-keyring X X X X
bash X X X X X X
btrfs-progs X X X X X
bubblewrap X X X X X X
ca-certificates X X X X X X
coreutils X X X X X X
cpio X X X X X X
curl X X X X X X
debian-keyring X X X X X
diffutils X X X X X X
distribution-gpg-keys X X X
dnf X X X X X X
dnf-plugins-core X X X
dnf5 X
dnf5-plugins X
dosfstools X X X X X X
e2fsprogs X X X X X X
edk2-ovmf X X X X X X
erofs-utils X X X X X
kmod X X X X X X
less X X X X X X
mtools X X X X X X
nano X X X X X X
openssh X X X X X X
openssl X X X X X X
pacman X X X X
pesign X X X X X X
policycoreutils X X X X X
qemu X X X X X X
sbsigntools X X X X X
socat X X X X X X
squashfs-tools X X X X X X
strace X X X X X X
swtpm X X X X X X
systemd X X X X X X
ukify X X X X X
tar X X X X X X
ubuntu-keyring X X X X X
util-linux X X X X X X
virtiofsd X X X X
xfsprogs X X X X X X
xz X X X X X X
zstd X X X X X X
zypper X X X X
ToolsTreeDistribution=, --tools-tree-distribution=
Set the distribution to use for the default tools tree. By default, the same distribution as the
image that’s being built is used, except for CentOS and Ubuntu images, in which case Fedora and
Debian are used respectively.
ToolsTreeRelease=, --tools-tree-release=
Set the distribution release to use for the default tools tree. By default, the hardcoded default
release in mkosi for the distribution is used.
ToolsTreeMirror=, --tools-tree-mirror=
Set the mirror to use for the default tools tree. By default, the default mirror for the tools
tree distribution is used.
ToolsTreePackages=, --tools-tree-packages=
Extra packages to install into the default tools tree. Takes a comma separated list of package
specifications. This option may be used multiple times in which case the specified package lists
are combined.
RuntimeTrees=, --runtime-tree=
Takes a colon separated pair of paths. The first path refers to a directory to mount into any ma‐
chine (container or VM) started by mkosi. The second path refers to the target directory inside
the machine. If the second path is not provided, the directory is mounted below /root/src in the
machine. If the second path is relative, it is interpreted relative to /root/src in the machine.
For each mounted directory, the uid and gid of the user running mkosi are mapped to the root user
in the machine. This means that all the files and directories will appear as if they’re owned by
root in the machine, and all new files and directories created by root in the machine in these di‐
rectories will be owned by the user running mkosi on the host. Note that when using mkosi qemu
with this feature systemd v254 or newer has to be installed in the image.
RuntimeSize=, --runtime-size=
If specified, disk images are grown to the specified size before they’re booted with systemd-
nspawn or qemu. Takes a size in bytes. Additionally, the suffixes K, M and G can be used to
specify a size in kilobytes, megabytes and gigabytes respectively.
RuntimeScratch=: --runtime-scratch=
Takes a boolean value or auto. Specifies whether to mount extra scratch space to /var/tmp. If
enabled, practically unlimited scratch space is made available under /var/tmp when booting the im‐
age with mkosi qemu, mkosi boot or mkosi shell. Note that using this feature with mkosi qemu re‐
quires systemd v254 or newer in the guest.
SshKey=, --ssh-key=
Path to the X509 private key in PEM format to use to connect to a virtual machine started with
mkosi qemu and built with the Ssh= option enabled via the mkosi ssh command. If not configured
and mkosi.key exists in the working directory, it will automatically be used for this purpose.
Run mkosi genkey to automatically generate a key in mkosi.key.
SshCertificate=, --ssh-certificate=
Path to the X509 certificate in PEM format to provision as the SSH public key in virtual machines
started with mkosi qemu. If not configured and mkosi.crt exists in the working directory, it will
automatically be used for this purpose. Run mkosi genkey to automatically generate a certificate
in mkosi.crt.
Specifiers
The current value of various settings can be accessed when parsing configuration files by using speci‐
fiers. To write a literal % character in a configuration file without treating it as a specifier, use
%%. The following specifiers are understood:
Setting Specifier
─────────────────────────────
Distribution= %d
Release= %r
Architecture= %a
Format= %t
Output= %o
OutputDirectory= %O
ImageId= %i
ImageVersion= %v
Supported distributions
Images may be created containing installations of the following distributions:
• Fedora Linux
• Debian
• Ubuntu
• Arch Linux
• openSUSE
• Mageia
• CentOS
• RHEL
• RHEL UBI
• OpenMandriva
• Rocky Linux
• Alma Linux
• Gentoo (Gentoo is experimental and unsupported. We make no guarantee that it will work at all and the
core maintainers will generally not fix gentoo specific issues)
• None (Requires the user to provide a pre-built rootfs)
In theory, any distribution may be used on the host for building images containing any other distribu‐
tion, as long as the necessary tools are available. Specifically, any distribution that packages apt may
be used to build Debian or Ubuntu images. Any distribution that packages dnf may be used to build images
for any of the rpm-based distributions. Any distro that packages pacman may be used to build Arch Linux
images. Any distribution that packages zypper may be used to build openSUSE images. Other distributions
and build automation tools for embedded Linux systems such as Buildroot, OpenEmbedded and Yocto Project
may be used by selecting the custom distribution, and populating the rootfs via a combination of base
trees, skeleton trees, and prepare scripts.
Currently, Fedora Linux packages all relevant tools as of Fedora 28.
Note that when not using a custom mirror, RHEL images can only be built from a host system with a RHEL
subscription (established using e.g. subscription-manager).
Execution Flow
Execution flow for mkosi build. Default values/calls are shown in parentheses. When building with --in‐
cremental mkosi creates a cache of the distribution installation if not already existing and replaces the
distribution installation in consecutive runs with data from the cached one.
1. Parse CLI options
2. Parse configuration files
3. If we’re not running as root, unshare the user namespace and map the subuid range configured in
/etc/subuid and /etc/subgid into it.
4. Unshare the mount namespace
5. Remount the following directories read-only if they exist:
• /usr
• /etc
• /opt
• /srv
• /boot
• /efi
• /media
• /mnt
Then, for each image, we execute the following steps:
1. Copy package manager trees into the workspace
2. Copy base trees (--base-tree=) into the image
3. Copy skeleton trees (mkosi.skeleton) into image
4. Install distribution and packages into image or use cache tree if available
5. Run prepare scripts on image with the final argument (mkosi.prepare)
6. Install build packages in overlay if any build scripts are configured
7. Run prepare scripts on overlay with the build argument if any build scripts are configured
(mkosi.prepare)
8. Cache the image if configured (--incremental)
9. Run build scripts on image + overlay if any build scripts are configured (mkosi.build)
10. Finalize the build if the output format none is configured
11. Copy the build scripts outputs into the image
12. Copy the extra trees into the image (mkosi.extra)
13. Run post-install scripts (mkosi.postinst)
14. Write config files required for Ssh=, Autologin= and MakeInitrd=
15. Install systemd-boot and configure secure boot if configured (--secure-boot)
16. Run systemd-sysusers
17. Run systemd-tmpfiles
18. Run systemctl preset-all
19. Run depmod
20. Run systemd-firstboot
21. Run systemd-hwdb
22. Remove packages and files (RemovePackages=, RemoveFiles=)
23. Run SELinux relabel is a SELinux policy is installed
24. Run finalize scripts (mkosi.finalize)
25. Generate unified kernel image if configured to do so
26. Generate final output format
Scripts
To allow for image customization that cannot be implemented using mkosi’s builtin features, mkosi sup‐
ports running scripts at various points during the image build process that can customize the image as
needed. Scripts are executed on the host system as root (either real root or root within the user name‐
space that mkosi created when running unprivileged) with a customized environment to simplify modifying
the image. For each script, the configured build sources (BuildSources=) are mounted into the current
working directory before running the script in the current working directory. $SRCDIR is set to point to
the current working directory. The following scripts are supported:
• If mkosi.prepare (PrepareScripts=) exists, it is first called with the final argument, right after the
software packages are installed. It is called a second time with the build command line parameter,
right after the build packages are installed and the build overlay mounted on top of the image’s root
directory . This script has network access and may be used to install packages from other sources than
the distro’s package manager (e.g. pip, npm, ...), after all software packages are installed but before
the image is cached (if incremental mode is enabled). In contrast to a general purpose installation,
it is safe to install packages to the system (pip install, npm install -g) instead of in $SRCDIR itself
because the build image is only used for a single project and can easily be thrown away and rebuilt so
there’s no risk of conflicting dependencies and no risk of polluting the host system.
• If mkosi.build (BuildScripts=) exists, it is executed with the build overlay mounted on top of the im‐
age’s root directory. When running the build script, $DESTDIR points to a directory where the script
should place any files generated it would like to end up in the image. Note that make/automake/meson
based build systems generally honor $DESTDIR, thus making it very natural to build source trees from
the build script. After running the build script, the contents of $DESTDIR are copied into the image.
• If mkosi.postinst (PostInstallationScripts=) exists, it is executed after the (optional) build tree and
extra trees have been installed. This script may be used to alter the images without any restrictions,
after all software packages and built sources have been installed.
• If mkosi.finalize (FinalizeScripts=) exists, it is executed as the last step of preparing an image.
If a script uses the .chroot extension, mkosi will chroot into the image using mkosi-chroot (see below)
before executing the script. For example, if mkosi.postinst.chroot exists, mkosi will chroot into the
image and execute it as the post-installation script.
Scripts executed by mkosi receive the following environment variables:
• $ARCHITECTURE contains the architecture from the Architecture= setting. If Architecture= is not set,
it will contain the native architecture of the host machine. See the documentation of Architecture=
for possible values for this variable.
• $CHROOT_SCRIPT contains the path to the running script relative to the image root directory. The pri‐
mary usecase for this variable is in combination with the mkosi-chroot script. See the description of
mkosi-chroot below for more information.
• $SRCDIR contains the path to the directory mkosi was invoked from, with any configured build sources
mounted on top. $CHROOT_SRCDIR contains the value that $SRCDIR will have after invoking mkosi-chroot.
• $BUILDDIR is only defined if mkosi.builddir exists and points to the build directory to use. This is
useful for all build systems that support out-of-tree builds to reuse already built artifacts from pre‐
vious runs. $CHROOT_BUILDDIR contains the value that $BUILDDIR will have after invoking mkosi-chroot.
• $DESTDIR is a directory into which any installed software generated by a build script may be placed.
This variable is only set when executing a build script. $CHROOT_DESTDIR contains the value that
$DESTDIR will have after invoking mkosi-chroot.
• $OUTPUTDIR points to the staging directory used to store build artifacts generated during the build.
$CHROOT_OUTPUTDIR contains the value that $OUTPUTDIR will have after invoking mkosi-chroot.
• $PACKAGEDIR points to the directory containing the local package repository. Build scripts can add
more packages to the local repository by writing the packages to $PACKAGEDIR.
• $BUILDROOT is the root directory of the image being built, optionally with the build overlay mounted on
top depending on the script that’s being executed.
• $WITH_DOCS is either 0 or 1 depending on whether a build without or with installed documentation was
requested (WithDocs=yes). A build script should suppress installation of any package documentation to
$DESTDIR in case $WITH_DOCS is set to 0.
• $WITH_TESTS is either 0 or 1 depending on whether a build without or with running the test suite was
requested (WithTests=no). A build script should avoid running any unit or integration tests in case
$WITH_TESTS is 0.
• $WITH_NETWORK is either 0 or 1 depending on whether a build without or with networking is being execut‐
ed (WithNetwork=no). A build script should avoid any network communication in case $WITH_NETWORK is 0.
• $SOURCE_DATE_EPOCH is defined if requested (SourceDateEpoch=TIMESTAMP, Environ‐
ment=SOURCE_DATE_EPOCH=TIMESTAMP or the host environment variable $SOURCE_DATE_EPOCH). This is useful
to make builds reproducible. See SOURCE_DATE_EPOCH (https://reproducible-builds.org/specs/source-date-
epoch/) for more information.
• $MKOSI_UID and $MKOSI_GID are the respectively the uid, gid of the user that invoked mkosi, potentially
translated to a uid in the user namespace that mkosi is running in. These can be used in combination
with setpriv to run commands as the user that invoked mkosi (e.g. setpriv --reuid=$MKOSI_UID
--regid=$MKOSI_GID --clear-groups <command>)
Consult this table for which script receives which environment variables:
Variable mkosi.prepare mkosi.build mkosi.postinst mkosi.finalize
───────────────────────────────────────────────────────────────────────────────────
$CHROOT_SCRIPT X X X X
$SRCDIR X X X X
CHROOT_SRCDIR X X X X
$BUILDDIR X
CHROOT_BUILDDIR X
DESTDIR X
CHROOT_DESTDIR X
$OUTPUTDIR X X X
CHROOT_OUTPUTDIR X X X
$BUILDROOT X X X X
WITH_DOCS X X
WITH_TESTS X X
WITH_NETWORK X X
SOURCE_DATE_EPOCH X X X X
MKOSI_UID X X X X
MKOSI_GID X X X X
Additionally, when a script is executed, a few scripts are made available via $PATH to simplify common
usecases.
• mkosi-chroot: This script will chroot into the image and execute the given command. On top of chroot‐
ing into the image, it will also mount various files and directories ($SRCDIR, $DESTDIR, $BUILDDIR,
$OUTPUTDIR, $CHROOT_SCRIPT) into the image and modify the corresponding environment variables to point
to the locations inside the image. It will also mount APIVFS filesystems (/proc, /dev, ...) to make
sure scripts and tools executed inside the chroot work properly. It also propagates /etc/resolv.conf
from the host into the chroot if requested so that DNS resolution works inside the chroot. After the
mkosi-chroot command exits, various mount points are cleaned up.
For example, to invoke ls inside of the image, use the following
mkosi-chroot ls ...
To execute the entire script inside the image, add a “.chroot” suffix to the name (mkosi.build.chroot
instead of mkosi.build, etc.).
• For all of the supported package managers except portage (dnf, rpm, apt, pacman, zypper), scripts of
the same name are put into $PATH that make sure these commands operate on the image’s root directory
with the configuration supplied by the user instead of on the host system. This means that from a
script, you can do e.g. dnf install vim to install vim into the image.
• mkosi-as-caller: This script uses setpriv to switch from the user root in the user namespace used for
various build steps back to the original user that called mkosi. This is useful when we want to invoke
build steps which will write to $BUILDDIR and we want to have the files owned by the calling user.
For example, a complete mkosi.build script might be the following:
set -ex
mkosi-as-caller meson setup "$BUILDDIR/build" "$SRCDIR"
mkosi-as-caller meson compile -C "$BUILDDIR/build"
meson install -C "$BUILDDIR/build" --no-rebuild
• git is automatically invoked with safe.directory=* to avoid permissions errors when running as the root
user in a user namespace.
• useradd and groupadd are automatically invoked with --root=$BUILDROOT when executed outside of the im‐
age.
When scripts are executed, any directories that are still writable are also made read-only (/home, /var,
/root, ...) and only the minimal set of directories that need to be writable remain writable. This is
to ensure that scripts can’t mess with the host system when mkosi is running as root.
Note that when executing scripts, all source directories are made ephemeral which means all changes made
to source directories while running scripts are thrown away after the scripts finish executing. Use the
output, build or cache directories if you need to persist data between builds.
Files
To make it easy to build images for development versions of your projects, mkosi can read configuration
data from the local directory, under the assumption that it is invoked from a source tree. Specifically,
the following files are used if they exist in the local directory:
• The mkosi.skeleton/ directory or mkosi.skeleton.tar archive may be used to insert files into the image.
The files are copied before the distribution packages are installed into the image. This allows cre‐
ation of files that need to be provided early, for example to configure the package manager or set sys‐
temd presets.
When using the directory, file ownership is not preserved: all files copied will be owned by root. To
preserve ownership, use a tar archive.
• The mkosi.extra/ directory or mkosi.extra.tar archive may be used to insert additional files into the
image, on top of what the distribution includes in its packages. They are similar to mkosi.skeleton/
and mkosi.skeleton.tar, but the files are copied into the directory tree of the image after the OS was
installed.
When using the directory, file ownership is not preserved: all files copied will be owned by root. To
preserve ownership, use a tar archive.
• The mkosi.nspawn nspawn settings file will be copied into the same place as the output image file, if
it exists. This is useful since nspawn looks for settings files next to image files it boots, for ad‐
ditional container runtime settings.
• The mkosi.cache/ directory, if it exists, is automatically used as package download cache, in order to
speed repeated runs of the tool.
• The mkosi.builddir/ directory, if it exists, is automatically used as out-of-tree build directory, if
the build commands in the mkosi.build scripts support it. Specifically, this directory will be mounted
into the build container, and the $BUILDDIR environment variable will be set to it when the build
scripts are invoked. A build script may then use this directory as build directory, for automake-style
or ninja-style out-of-tree builds. This speeds up builds considerably, in particular when mkosi is
used in incremental mode (-i): not only the image and build overlay, but also the build tree is reused
between subsequent invocations. Note that if this directory does not exist the $BUILDDIR environment
variable is not set, and it is up to the build scripts to decide whether to do in in-tree or an out-of-
tree build, and which build directory to use.
• The mkosi.rootpw file can be used to provide the password for the root user of the image. If the pass‐
word is prefixed with hashed: it is treated as an already hashed root password. The password may op‐
tionally be followed by a newline character which is implicitly removed. The file must have an access
mode of 0600 or less. If this file does not exist, the distribution’s default root password is set
(which usually means access to the root user is blocked).
• The mkosi.passphrase file provides the passphrase to use when LUKS encryption is selected. It should
contain the passphrase literally, and not end in a newline character (i.e. in the same format as crypt‐
setup and /etc/crypttab expect the passphrase files). The file must have an access mode of 0600 or
less.
• The mkosi.crt and mkosi.key files contain an X.509 certificate and PEM private key to use when signing
is required (UEFI SecureBoot, verity, ...).
• The mkosi.output/ directory is used to store all build artifacts.
• The mkosi.credentials/ directory is used as a source of extra credentials similar to the Credentials=
option. For each file in the directory, the filename will be used as the credential name and the file
contents become the credential value, or, if the file is executable, mkosi will execute the file and
the command’s output to stdout will be used as the credential value. Output to stderr will be ignored.
Credentials configured with Credentials= take precedence over files in mkosi.credentials.
• The mkosi.repart/ directory is used as the source for systemd-repart partition definition files which
are passed to systemd-repart when building a disk image. If it does not exist and the RepartDirecto‐
ries= setting is not configured, mkosi will default to the following partition definition files:
00-esp.conf (if we’re building a bootable image):
[Partition]
Type=esp
Format=vfat
CopyFiles=/boot:/
CopyFiles=/efi:/
SizeMinBytes=512M
SizeMaxBytes=512M
05-bios.conf (if we’re building a BIOS bootable image):
[Partition]
# UUID of the grub BIOS boot partition which grubs needs on GPT to
# embed itself into.
Type=21686148-6449-6e6f-744e-656564454649
SizeMinBytes=1M
SizeMaxBytes=1M
10-root.conf:
[Partition]
Type=root
Format=<distribution-default-filesystem>
CopyFiles=/
Minimize=guess
Note that if either mkosi.repart/ is found or RepartDirectories= is used, we will not use any of the
default partition definitions.
All these files are optional.
Note that the location of all these files may also be configured during invocation via command line
switches, and as settings in mkosi.conf, in case the default settings are not acceptable for a project.
CACHING
mkosi supports three different caches for speeding up repetitive re-building of images. Specifically:
1. The package cache of the distribution package manager may be cached between builds. This is config‐
ured with the --cache-dir= option or the mkosi.cache/ directory. This form of caching relies on the
distribution’s package manager, and caches distribution packages (RPM, DEB, ...) after they are down‐
loaded, but before they are unpacked.
2. If the incremental build mode is enabled with --incremental, cached copies of the final image and
build overlay are made immediately before the build sources are copied in (for the build overlay) or
the artifacts generated by mkosi.build are copied in (in case of the final image). This form of
caching allows bypassing the time-consuming package unpacking step of the distribution package man‐
agers, but is only effective if the list of packages to use remains stable, but the build sources and
its scripts change regularly. Note that this cache requires manual flushing: whenever the package
list is modified the cached images need to be explicitly removed before the next re-build, using the
-f switch.
3. Finally, between multiple builds the build artifact directory may be shared, using the mkosi.builddir/
directory. This directory allows build systems such as Meson to reuse already compiled sources from a
previous built, thus speeding up the build process of a mkosi.build build script.
The package cache and incremental mode are unconditionally useful. The final cache only apply to uses of
mkosi with a source tree and build script. When all three are enabled together turn-around times for
complete image builds are minimal, as only changed source files need to be recompiled.
Building multiple images
If the mkosi.images/ directory exists, mkosi will load individual image configurations from it and build
each of them. Image configurations can be either directories containing mkosi configuration files or
regular files with the .conf extension.
When image configurations are found in mkosi.images/, mkosi will build the configured images and all of
their dependencies (or all of them if no images were explicitly configured using Images=). To add depen‐
dencies between images, the Dependencies= setting can be used.
When images are defined, mkosi will first read the global configuration (configuration outside of the
mkosi.images/ directory), followed by the image specific configuration. This means that global configu‐
ration takes precedence over image specific configuration.
Images can refer to outputs of images they depend on. Specifically, for the following options, mkosi
will only check whether the inputs exist just before building the image:
• BaseTrees=
• PackageManagerTrees=
• SkeletonTrees=
• ExtraTrees=
• ToolsTree=
• Initrds=
To refer to outputs of a image’s dependencies, simply configure any of these options with a relative path
to the output to use in the output directory of the dependency. Or use the %O specifier to refer to the
output directory.
A good example on how to build multiple images can be found in the systemd (https://github.com/sys‐
temd/systemd/tree/main/mkosi.images) repository.
ENVIRONMENT VARIABLES
• $MKOSI_LESS overrides options for less when it is invoked by mkosi to page output.
• $MKOSI_DNF can be used to override the executable used as dnf. This is particularly useful to select
between dnf and dnf5.
EXAMPLES
Create and run a raw GPT image with ext4, as image.raw:
# mkosi -p systemd --incremental boot
Create and run a bootable GPT image, as foobar.raw:
$ mkosi -d fedora -p kernel-core -p systemd -p systemd-boot -p udev -o foobar.raw
# mkosi --output foobar.raw boot
$ mkosi --output foobar.raw qemu
Create and run a Fedora Linux image in a plain directory:
# mkosi --distribution fedora --format directory boot
Create a compressed image image.raw.xz with SSH installed and add a checksum file:
$ mkosi --distribution fedora --format disk --checksum --compress-output --package=openssh-clients
Inside the source directory of an automake-based project, configure mkosi so that simply invoking mkosi
without any parameters builds an OS image containing a built version of the project in its current state:
$ cat >mkosi.conf <<EOF
[Distribution]
Distribution=fedora
[Output]
Format=disk
[Content]
Packages=kernel,systemd,systemd-udev,openssh-clients,httpd
BuildPackages=make,gcc,libcurl-devel
EOF
$ cat >mkosi.build <<EOF
#!/bin/sh
if [ "$container" != "mkosi" ]; then
exec mkosi-chroot "$CHROOT_SCRIPT" "$@"
fi
cd $SRCDIR
./autogen.sh
./configure --prefix=/usr
make -j `nproc`
make install
EOF
$ chmod +x mkosi.build
# mkosi --incremental boot
# systemd-nspawn -bi image.raw
Different ways to boot with qemu
The easiest way to boot a virtual machine is to build an image with the required components and let mkosi
call qemu with all the right options:
$ mkosi -d fedora \
--autologin \
-p systemd-udev,systemd-boot,kernel-core \
build
$ mkosi -d fedora qemu
...
fedora login: root (automatic login)
[root@fedora ~]#
The default is to boot with a text console only. In this mode, messages from the boot loader, the ker‐
nel, and systemd, and later the getty login prompt and shell all use the same terminal. It is possible
to switch between the qemu console and monitor by pressing Ctrl-a c. The qemu monitor may for example be
used to inject special keys or shut down the machine quickly.
To boot with a graphical window, add --qemu-qui:
$ mkosi -d fedora --qemu-gui qemu
A kernel may be booted directly with mkosi qemu -kernel ... -initrd ... -append '...'. This is a bit
faster because no boot loader is used, and it is also easier to experiment with different kernels and
kernel commandlines. Note that despite the name, qemu’s -append option replaces the default kernel com‐
mandline embedded in the kernel and any previous -append specifications.
The UKI is also copied into the output directory and may be booted directly:
$ mkosi qemu -kernel mkosi.output/fedora~38/image.efi
When booting using an external kernel, we don’t need the kernel in the image, but we would still want the
kernel modules to be installed.
It is also possible to do a direct kernel boot into a boot loader, taking advantage of the fact that sys‐
temd-boot(7) is a valid UEFI binary:
$ mkosi qemu -kernel /usr/lib/systemd/boot/efi/systemd-bootx64.efi
In this scenario, the kernel is loaded from the ESP in the image by systemd-boot.
REQUIREMENTS
mkosi is packaged for various distributions: Debian, Ubuntu, Arch Linux, Fedora Linux, OpenMandriva, Gen‐
too. Note that it has been a while since the last release and the packages shipped by distributions are
very out of date. We currently recommend running mkosi from git until a new release happens.
mkosi currently requires systemd 254 to build bootable disk images.
When not using distribution packages make sure to install the necessary dependencies. For example, on
Fedora Linux you need:
# dnf install bubblewrap btrfs-progs apt dosfstools mtools edk2-ovmf e2fsprogs squashfs-tools gnupg python3 tar xfsprogs xz zypper sbsigntools
On Debian/Ubuntu it might be necessary to install the ubuntu-keyring, ubuntu-archive-keyring and/or de‐
bian-archive-keyring packages explicitly, in addition to apt, depending on what kind of distribution im‐
ages you want to build.
Note that the minimum required Python version is 3.9.
Frequently Asked Questions (FAQ)
• Why does mkosi qemu with KVM not work on Debian/Ubuntu?
While other distributions are OK with allowing access to /dev/kvm, on Debian/Ubuntu this is only allowed
for users in the kvm group. Because mkosi unshares a user namespace when running unprivileged, even if
the calling user was in the kvm group, when mkosi unshares the user namespace to run unprivileged, it
loses access to the kvm group and by the time we start qemu we don’t have access to /dev/kvm anymore. As
a workaround, you can change the permissions of the device nodes to 0666 which is sufficient to make KVM
work unprivileged. To persist these settings across reboots, copy /usr/lib/tmpfiles.d/static-nodes-per‐
missions.conf to /etc/tmpfiles.d/static-nodes-permissions.conf and change the mode of /dev/kvm from 0660
to 0666.
REFERENCES
• Primary mkosi git repository on GitHub (https://github.com/systemd/mkosi/)
• mkosi — A Tool for Generating OS Images (https://0pointer.net/blog/mkosi-a-tool-for-generating-os-im‐
ages.html) introductory blog post by Lennart Poettering
• The mkosi OS generation tool (https://lwn.net/Articles/726655/) story on LWN
SEE ALSO
systemd-nspawn(1), dnf(8)
mkosi(1)