mkosi(1) mkosi(1)

mkosi — Build Bespoke OS Images

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...] dependencies

mkosi [options...] help

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.

The following command line verbs are known:

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.
This builds the image based on the settings passed in on the command line or read from configuration 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.
This builds the image if it is not built yet, and then invokes systemd-nspawn to acquire an interactive 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 unconditionally before acquiring the shell, see below. This command must be executed as root.
Similar to shell, but boots the image using systemd-nspawn. An optional command line may be specified 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.
Similar to boot, but uses the configured virtual machine monitor (by default qemu) to boot up the image, i.e. instead of container virtualization virtual machine virtualization is used. How extra command line arguments are interpreted depends on the configured virtual machine monitor. See VirtualMachineMonitor= for more information.
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 arguments passed after the ssh verb are passed as arguments to the ssh invocation. To connect to a container, use machinectl login or machinectl shell.

The Machine= option can be used to give the machine a custom hostname when booting it which can later be used to ssh into the image (e.g. mkosi --machine=mymachine qemu followed by mkosi --machine=mymachine ssh).

Uses journalctl to inspect the journal inside the image. Any arguments specified after the journalctl verb are appended to the journalctl invocation.

If ForwardJournal= is specified, this verb will operate on the forwarded journal instead of the journal inside the image.

Uses coredumpctl to look for coredumps inside the image. Any arguments specified after the coredumpctl verb are appended to the coredumpctl invocation.

If ForwardJournal= is specified, this verb will operate on the forwarded journal instead of the image. Note that this requires configuring systemd-coredump to store coredumps in the journal.

Remove build artifacts generated on a previous build. If combined with -f, also removes incremental build cache images. If -f is specified twice, also removes any package cache.
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 machinectl pull-tar ....
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.
Bumps the image version from mkosi.version and writes the resulting version string to mkosi.version. 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.
Generate a pair of SecureBoot keys for usage with the SecureBootKey=/--secure-boot-key= and SecureBootCertificate=/--secure-boot-certificate= options.
Show mkosi’s documentation. By default this verb will try several ways to output the documentation, but a specific option can be chosen with the --doc-format option. Distro packagers are encouraged 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.
Output the list of packages required by mkosi to build and boot images.

This list can be piped directly to a package manager to install the packages. For example, if the host system uses the dnf package manager, the packages could be installed as follows:

mkosi dependencies | xargs -d '\n' dnf install
This verb is equivalent to the --help switch documented below: it shows a brief usage explanation.

Those settings cannot be configured in the configuration files.

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 removed, too, before the re-build is initiated. If a package cache is used (also see the Files section 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 removed.
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.
Enable additional debugging output.
When executing a command in the image fails, mkosi will start an interactive shell in the image allowing further debugging.
When an error occurs, the workspace directory will not be deleted.
Show package version.
Show brief usage information.
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.
Number of days that the keys should remain valid when generating keys via mkosi’s genkey command. Defaults to two years (730 days).
If specified, after each successful build 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 management: each build in a series will have a version number one higher then the previous one.
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, system.
Show the summary output as JSON-SEQ.

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.

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-letter shortcut is also allowed. In the configuration files, the setting must be in the appropriate section, 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.
•
If a profile is defined, its configuration is parsed from the mkosi.profiles/ directory.
•
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.
•
Subimages are parsed from the mkosi.images directory if it exists.

Note that settings configured via the command line always override settings configured via configuration files. If the same setting is configured more than once via configuration files, later assignments override earlier assignments except for settings that take a collection of values. Also, settings read from mkosi.local.conf will override settings from configuration files that are parsed later but not settings specified on the CLI.

Settings that take a collection 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 overrides any configured default values as well. The values specified on the CLI are appended after all the values from configuration files.

To conditionally include configuration files, the [Match] section can be used. A [Match] section consists of individual conditions. Conditions can use a pipe symbol (|) after the equals sign (...=|...), which causes the condition to become a triggering condition. The config file will be included if the logical AND of all non-triggering conditions and the logical OR of all triggering conditions is satisfied. To negate the result of a condition, prefix the argument with an exclamation 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] conditions compare 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 (settings specified on the CLI are taken into account). 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 conditions 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 conditions 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

The [TriggerMatch] section can be used to indicate triggering match sections. These are identical to triggering conditions except they apply to the entire match section instead of just a single condition. As an example, the following will match if the distribution is debian and the release is bookworm or if the distribution is ubuntu and the release is focal.

[TriggerMatch]
Distribution=debian
Release=bookworm
[TriggerMatch]
Distribution=ubuntu
Release=focal

The semantics of conditions in [TriggerMatch] sections is the same as in [Match], i.e. all normal conditions are joined by a logical AND and all triggering conditions are joined by a logical OR. When mixing [Match] and [TriggerMatch] sections, a match is achieved when all [Match] sections match and at least one [TriggerMatch] section matches. No match sections are valued as true. Logically this means:

(⋀ᵢ Matchᵢ) ∧ (⋁ᵢ TriggerMatchᵢ)

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.

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.
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. artful). 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.
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 foreign architecture, you’ll also need to install and register a user mode emulator for that architecture.

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.

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.pkgbuild.com http://mirror.archlinuxarm.org
opensuse http://download.opensuse.org
ubuntu http://archive.ubuntu.com http://ports.ubuntu.com
centos https://mirrors.centos.org
rocky https://mirrors.rockylinux.org
alma https://mirrors.almalinux.org
fedora https://mirrors.fedoraproject.org
rhel-ubi https://cdn-ubi.redhat.com
mageia https://www.mageia.org
openmandriva http://mirrors.openmandriva.org
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.
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.
Enable package repositories that are disabled by default. This can be used to enable the EPEL repos for CentOS or different components of the Debian/Ubuntu repositories.
Takes one of auto, metadata, always or never. Defaults to auto. If always, the package manager is instructed not to contact the network. This provides a minimal level of reproducibility, as long as the package cache is already fully populated. If set to metadata, the package manager can still download packages, but we won’t sync the repository metadata. If set to auto, the repository metadata is synced unless we have a cached image (see Incremental=) and packages can be downloaded during the build. If set to never, repository metadata is always synced and and packages can be downloaded during the build.
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. This option is similar to the SkeletonTrees= option, 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. If the mkosi.pkgmngr/ directory is found in the local directory it is used for this purpose with the root directory as target (also see the Files section below). If not configured in any way this value will default to the same value of SkeletonTrees=.

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 locations 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 image in your repository configuration.

The image format type to generate. One of directory (for generating an OS image directly in a local 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 unified kernel image with the OS image in the .initrd PE section), esp (uki but wrapped in a disk image with only an ESP partition), oci (a directory compatible with the OCI image specification), sysext, confext, portable or none (the OS image is solely intended as a build image to produce another artifact).

If the disk output format is used, the disk image is generated using systemd-repart. The repart partition definition files to use can be configured 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.

If the none output format is used, the outputs from a previous build are not removed, but clean scripts (see CleanScripts=) are still executed. This allows rerunning a build script (see BuildScripts=) without removing the results of a previous build.

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.
Name to use for the generated output image file or directory. Defaults to image or, if ImageId= is specified, it is used as the default output name, optionally suffixed with the version set with ImageVersion= or if a specific image is built from mkosi.images, the name of the image is preferred over ImageId. Note that this option does not allow configuring the output directory, use OutputDirectory= for that.

Note that this only specifies 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.

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 derivatives up to version 8, which default to xz, and OCI images, which default to gzip. 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, esp, and oci.
Configure the compression level to use. Takes an integer. The possible values depend on the compression being used.
Path to a directory where to place all generated artifacts. If this is not specified and the directory mkosi.output/ exists in the local directory, it is automatically used for this purpose.
Path to a directory where to store data required temporarily while building the image. This directory 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 invocation be aborted abnormally (for example, due to reboot/power failure).

Takes a path to a directory to use as the incremental cache directory for the incremental images produced when the Incremental= option is enabled. If this option is not used, but a mkosi.cache/ directory is found in the local directory it is automatically used for this purpose.
Takes a path to a directory to use as the package cache directory for the distribution package manager used. If unset, a suitable directory in the user’s home directory or system is used.
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 environment 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 directory mkosi.builddir/ exists in the local directory it is automatically used for this purpose (also see the Files section below).
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 default 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 /usr/lib/os-release or similar, in particular the IMAGE_VERSION= field of it).
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 image ID is automatically added to /usr/lib/os-release.
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.freedesktop.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.
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 directory, 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.
Override the default sector size that systemd-repart uses when building a disk image.
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.

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).

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.
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.
Takes a timestamp in seconds since the UNIX epoch as argument. File modification times of all files will be clamped to this value. The variable is also propagated to systemd-repart and scripts executed by mkosi. If not set explicitly, SOURCE_DATE_EPOCH from --environment and from the host environment are tried in that order. This is useful to make builds reproducible. See SOURCE_DATE_EPOCH (https://reproducible-builds.org/specs/source-date-epoch/) for more information.
Takes a comma-separated list of paths to executables that are used as the clean scripts for this image. See the Scripts section for more information.

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, package groups, and virtual provides, including file paths.

See PackageDirectories= for information on how to make local packages available for installation with Packages=.

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-*
         /usr/bin/ld
         @development-tools
         python3dist(mypy)
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.
Similar to Packages=, but packages configured with this setting are not cached when Incremental= is enabled and are installed after executing any build scripts.

Specifically, this setting can be used to install packages that change often or which are built by a build script.

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. If the mkosi.packages/ directory is found in the local directory it is also used for this purpose.
Like PackageDirectories=, but any changes to the packages in these directories will not invalidate the cached images if Incremental= is enabled.

Additionally, build scripts can add more packages to the local repository by placing the built packages in $PACKAGEDIR. The packages placed in $PACKAGEDIR are shared between all image builds and thus available for installation in all images using VolatilePackages=.

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.
Include documentation in the image. Enabled by default. When disabled, if the underlying distribution package manager supports it documentation is not included in the image. The $WITH_DOCS environment variable passed to the mkosi.build scripts is set to 0 or 1 depending on whether this option is enabled or disabled.
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 by setting CleanPackageMetadata=no (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.

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 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 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 directory 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.

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 target 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.

Takes a comma-separated list of package specifications for removal, in the same format as Packages=. The removal will be performed as one of the last steps. This step is skipped if CleanPackageMetadata=no is used.
Takes a comma-separated list of globs. Files in the image matching the globs will be purged at the end.
Enable/disable removal of package manager databases and repository metadata at the end of installation. Can be specified as true, false, or auto (the default). With auto, package manager databases and repository metadata will be removed if the respective package manager executable is not present at the end of the installation.
Takes a comma-separated list of paths to executables that are used as the sync scripts for this image. See the Scripts section for more information.
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.
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.
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.
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.
Takes a comma-separated list of paths to executables that are used as the post output scripts for this image. See the Scripts section for more information.
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 directory is mounted to /work/src.
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 directories will be reset to their original state every time after running all scripts of a specific type (except sync scripts).
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 environment 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.
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.
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.
When true, enables network connectivity while the build scripts mkosi.build are invoked. By default, 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.
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 either 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.
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 installed 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 chainloads 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 Bootloader= 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 architecture) 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 location by default.

Takes one of none or grub. Defaults to none. If set to none, no BIOS bootloader will be installed. If set to grub, grub is installed as the BIOS boot loader if a bootable image is requested 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 definition 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 BiosBootloader=.

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.

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 them. 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=).

Note that when this option is enabled, mkosi will only install already signed bootloader binaries, kernel image files and unified kernel images as self-signed binaries would not be accepted by the signed version of shim.

Specifies whether to use unified kernel images or not when Bootloader= is set to systemd-boot or grub. Takes a boolean value or auto. Defaults to auto. If enabled, unified kernel images are always used and the build will fail if any components required to build unified kernel images are missing. If set to auto, unified kernel images will be used if all necessary components are available. Otherwise Type 1 entries as defined by the Boot Loader Specification will be used instead. If disabled, Type 1 entries will always be used.
Takes a filename without any path components to specify the format that unified kernel images should be installed as. This may include both the regular specifiers (see Specifiers) and special delayed specifiers, that are expanded during the installation of the files, which are described below. The default format for this parameter is &e-&k with -&h being appended if roothash= or usrhash= is found on the kernel command line and +&c if /etc/kernel/tries is found in the image.

The following specifiers may be used:

Specifier Value
&& & character
&e Entry Token
&k Kernel version
&h roothash= or usrhash= value of kernel argument
&c Number of tries used for boot attempt counting
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 specified and a bootable image is requested, mkosi will look for initrds in a subdirectory io.mkosi.initrd of the artifact directory (see $ARTIFACTDIR in the section ENVIRONMENT VARIABLES), if none are found there mkosi will automatically build a default initrd.
Extra packages to install into the default initrd. Takes a comma separated list of package specifications. This option may be used multiple times in which case the specified package lists are combined.
Similar to VolatilePackages=, except it applies to the default initrd.
When set to true only include microcode for the host’s CPU in the image.
Use the specified kernel command line when building images.

If the value of this setting contains the literals root=PARTUUID or mount.usr=PARTUUID, these are replaced with the partition UUID of the root or usr partition respectively. For example, root=PARTUUID would be replaced with root=PARTUUID=58c7d0b2-d224-4834-a16f-e036322e88f7 where 58c7d0b2-d224-4834-a16f-e036322e88f7 is the partition UUID of the root partition.

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 anywhere 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 dependencies of the matched modules are included in the image as well.

If the special value default is used, the default kernel modules defined in the mkosi-initrd configuration are included as well.

If the special value host is used, the currently loaded modules on the host system are included 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.

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 excluded from the image.
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.
Like KernelModulesInclude=, but applies to the kernel modules included in the kernel modules initrd.
Like KernelModulesExclude=, but applies to the kernel modules included in the kernel modules initrd.
The settings Locale=, --locale=, LocaleMessages=, --locale-messages=, Keymap=, --keymap=, Timezone=, --timezone=, Hostname=, --hostname=, RootShell=, --root-shell= correspond to the identically named systemd-firstboot options. See the systemd firstboot manpage (https://www.freedesktop.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/credstore, so that they apply even if only /usr is shipped in the image.
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.
Enable autologin for the root user on /dev/pts/0 (nspawn), /dev/tty1 and /dev/hvc0.
Add /etc/initrd-release and /init to the image so that it can be used as an initramfs.
If specified, an sshd socket unit and matching service are installed in the final image that expose 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.
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 setfiles 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.

Sign systemd-boot (if it is not signed yet) and any generated unified kernel images for UEFI SecureBoot.
Set up automatic enrollment of the secure boot keys in virtual machines as documented in the systemd-boot man page (https://www.freedesktop.org/software/systemd/man/systemd-boot.html) if SecureBoot= is used. Note that systemd-boot will only do automatic secure boot key enrollment in virtual 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 supported on systemd versions older than v252. Defaults to yes.
Path to the PEM file containing the secret key for signing the UEFI kernel image if SecureBoot= is used and PCR signatures when SignExpectedPcr= is also used. When SecureBootKeySource= is specified, the input type depends on the source.
Source of SecureBootKey=, to support OpenSSL engines. E.g.: --secure-boot-key-source=engine:pkcs11
Path to the X.509 file containing the certificate for the signed UEFI kernel image, if SecureBoot= is used.
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.
Path to the PEM file containing the secret key for signing the verity signature, if a verity signature partition is added with systemd-repart. When VerityKeySource= is specified, the input type depends on the source.
Source of VerityKey=, to support OpenSSL engines. E.g.: --verity-key-source=engine:pkcs11
Path to the X.509 file containing the certificate for signing the verity signature, if a verity signature partition is added with systemd-repart.
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. Depends on SecureBoot= being enabled and key from SecureBootKey=.
Specify the path to a file containing the passphrase to use for LUKS encryption. It should contain 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.
Generate a SHA256SUMS file of all generated artifacts after the build is complete.
Sign the generated SHA256SUMS using gpg after completion.
Select the gpg key to use for signing SHA256SUMS. This key must be already present in the gpg keyring.

Configure a proxy to be used for all outgoing network connections. Various tools that mkosi invokes and for which the proxy can be configured are configured to use this proxy. mkosi also sets various well-known environment variables to specify the proxy to use for any programs it invokes that may need internet access.
Configure hostnames for which requests should not go through the proxy. Takes a comma separated list of hostnames.
Configure a file containing certificates used to verify the proxy. Defaults to the system-wide certificate store.

Currently, setting a proxy peer certificate is only supported when dnf or dnf5 is used to build the image.

Configure a file containing the certificate used to authenticate the client with the proxy.

Currently, setting a proxy client certificate is only supported when dnf or dnf5 is used to build the image.

Configure a file containing the private key used to authenticate the client with the proxy. Defaults to the proxy client certificate if one is provided.

Currently, setting a proxy client key is only supported when dnf or dnf5 is used to build the image.

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.
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 environment when the image is run. If this setting is not used but an mkosi.nspawn file found in the local directory it is automatically used for this purpose.
List of colon-separated paths to look for tools in, before using the regular $PATH search path.
Configures the virtual machine monitor to use. Takes one of qemu or vmspawn. Defaults to qemu.

When set to qemu, the image is booted with qemu. Most output formats can be booted in qemu. Any arguments specified after the verb are appended to the qemu invocation and are interpreted as extra qemu command line arguments.

When set to vmspawn, systemd-vmspawn is used to boot up the image, vmspawn only supports disk and directory type images. Any arguments specified after the verb are appended to the systemd-vmspawn invocation and are interpreted as extra vmspawn options and extra kernel command line arguments.

If enabled, qemu is executed with its graphical interface instead of with a serial console.
When used with the qemu verb, this options sets qemu’s -smp argument which controls the number of guest’s CPUs. Defaults to 2.

When set to 0, the number of CPUs available to the mkosi process will be used.

When used with the qemu verb, this options sets qemu’s -m argument which controls the amount of guest’s RAM. Defaults to 2G.
When used with the qemu verb, this option specifies whether QEMU should use KVM acceleration. Takes a boolean value or auto. Defaults to auto.
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.
When used with the qemu verb, this option specifies the vsock connection ID to use. Takes a number in the interval [3, 0xFFFFFFFF) or hash or auto. Defaults to auto. 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.
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.
When used with the qemu verb, this option specifies whether to attach the image to the virtual machine as a CD-ROM device. Takes a boolean. Defaults to no.
When used with the qemu verb, this option specifies which firmware to use. Takes one of uefi, uefi-secure-boot, bios, linux, or auto. Defaults to auto. When set to uefi, the OVMF firmware without secure boot support is used. When set to uefi-secure-boot, the OVMF firmware with secure boot support 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, uefi-secure-boot is used if possible and linux otherwise.
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 or uefi-secure-boot firmware is used. If not specified, mkosi will search for the default variables file and use that instead.

When set to microsoft, a firmware variables file with the Microsoft secure boot certificates already enrolled will be used.

When set to custom, the secure boot certificate from SecureBootCertificate= will be enrolled into the default firmware variables file.

virt-fw-vars from the virt-firmware (https://gitlab.com/kraxel/virt-firmware) project can be used to customize OVMF variable files.

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.

Add a qemu drive. Takes a colon-delimited string of format <id>:<size>[:<directory>[:<options>[:<file-id>]]]. id specifies the qemu ID assigned to the drive. This can be used as the drive= property in various qemu devices. size specifies the size of the drive. This 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. directory optionally specifies the directory in which to create the file backing the drive. options optionally specifies extra comma-delimited properties which are passed verbatim to qemu’s -drive option. file-id specifies the ID of the file backing the drive. Drives with the same file ID will share the backing file. The directory and size of the file will be determined from the first drive with a given file ID.

Example usage:

[Host]
QemuDrives=btrfs:10G
           ext4:20G
QemuArgs=-device nvme,serial=btrfs,drive=btrfs
         -device nvme,serial=ext4,drive=ext4
Space-delimited list of additional arguments to pass when invoking qemu.
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).
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 values which can be either key=value pairs or paths. If a path is provided, if it is a file, the credential name will be the name of the file. If the file is executable, the credential value will be the output of executing the file. Otherwise, the credential value will be the contents of the file. If the path is a directory, the same logic applies to each file in the directory.

Note that values will only be treated as paths if they do not contain the delimiter (=).

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.systemd.stub.kernel-cmdline-extra OEM string. This will only be picked up by systemd-boot/systemd-stub versions newer than or equal to v254.
If specified, ACLs will be set on any generated root filesystem directories that allow the user running mkosi to remove them without needing privileges.
If specified, programs executed by mkosi to build and boot an image 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 versions 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 directory it is automatically used for this purpose with the root directory as target.

Note if a binary is found in any of the paths configured with ExtraSearchPaths=, the binary will be executed on the host.

If set to default, mkosi will automatically add an extra tools tree image and use it as the tools tree.

Note that mkosi will only build a single default tools tree per build, even if multiple images are defined in mkosi.images with ToolsTree=default. The settings of the “last” image will apply to the default tools tree (usually the image defined last in mkosi.images and without any dependencies on other images).

The following table shows for which distributions default tools tree packages are defined and which packages are included in those default tools trees:

Fedora CentOS Debian Ubuntu Arch openSUSE
acl ✓ ✓ ✓ ✓ ✓ ✓
apt ✓ ✓ ✓ ✓ ✓
archlinux-keyring ✓ ✓ ✓ ✓ ✓
attr ✓ ✓ ✓ ✓ ✓ ✓
bash ✓ ✓ ✓ ✓ ✓ ✓
btrfs-progs ✓ ✓ ✓ ✓ ✓
bubblewrap ✓ ✓ ✓ ✓ ✓ ✓
ca-certificates ✓ ✓ ✓ ✓ ✓ ✓
coreutils ✓ ✓ ✓ ✓ ✓ ✓
cpio ✓ ✓ ✓ ✓ ✓ ✓
curl ✓ ✓ ✓ ✓ ✓ ✓
debian-keyring ✓ ✓ ✓ ✓ ✓
diffutils ✓ ✓ ✓ ✓ ✓ ✓
distribution-gpg-keys ✓ ✓ ✓ ✓
dnf ✓ ✓ ✓ ✓ ✓ ✓
dnf-plugins-core ✓ ✓ ✓
dnf5 ✓
dnf5-plugins ✓
dosfstools ✓ ✓ ✓ ✓ ✓ ✓
e2fsprogs ✓ ✓ ✓ ✓ ✓ ✓
edk2-ovmf ✓ ✓ ✓ ✓ ✓ ✓
erofs-utils ✓ ✓ ✓ ✓ ✓
findutils ✓ ✓ ✓ ✓ ✓ ✓
git ✓ ✓ ✓ ✓ ✓ ✓
grep ✓ ✓ ✓ ✓ ✓ ✓
grub-tools ✓ ✓ ✓ ✓ ✓
jq ✓ ✓ ✓ ✓ ✓ ✓
kmod ✓ ✓ ✓ ✓ ✓ ✓
less ✓ ✓ ✓ ✓ ✓ ✓
mtools ✓ ✓ ✓ ✓ ✓ ✓
nano ✓ ✓ ✓ ✓ ✓ ✓
openssh ✓ ✓ ✓ ✓ ✓ ✓
openssl ✓ ✓ ✓ ✓ ✓ ✓
sed ✓ ✓ ✓ ✓ ✓ ✓
pacman ✓ ✓ ✓ ✓ ✓
pesign ✓ ✓ ✓ ✓ ✓ ✓
policycoreutils ✓ ✓ ✓ ✓ ✓
qemu ✓ ✓ ✓ ✓ ✓ ✓
sbsigntools ✓ ✓ ✓ ✓ ✓ ✓
socat ✓ ✓ ✓ ✓ ✓ ✓
squashfs-tools ✓ ✓ ✓ ✓ ✓ ✓
strace ✓ ✓ ✓ ✓ ✓ ✓
swtpm ✓ ✓ ✓ ✓ ✓ ✓
systemd ✓ ✓ ✓ ✓ ✓ ✓
ukify ✓ ✓ ✓ ✓ ✓ ✓
tar ✓ ✓ ✓ ✓ ✓ ✓
ubuntu-keyring ✓ ✓ ✓ ✓ ✓
util-linux ✓ ✓ ✓ ✓ ✓ ✓
virtiofsd ✓ ✓ ✓ ✓ ✓ ✓
virt-firmware ✓ ✓ ✓
xfsprogs ✓ ✓ ✓ ✓ ✓ ✓
xz ✓ ✓ ✓ ✓ ✓ ✓
zstd ✓ ✓ ✓ ✓ ✓ ✓
zypper ✓ ✓ ✓ ✓
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.
Set the distribution release to use for the default tools tree. By default, the hardcoded default release in mkosi for the distribution is used.
Set the mirror to use for the default tools tree. By default, the default mirror for the tools tree distribution is used.
Same as Repositories= but for the default tools tree.
Same as PackageManagerTrees= but for the default tools tree.
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.
Specify whether to use certificates and keys from the tools tree. If enabled, /usr/share/keyrings, /usr/share/distribution-gpg-keys, /etc/pki, /etc/ssl, /etc/ca-certificates, /etc/pacman.d/gnupg and /var/lib/ca-certificates from the tools tree are used. Otherwise, these directories are picked up from the host.
Takes a colon separated pair of paths. The first path refers to a directory to mount into any machine (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 at /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 directories 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.

If specified, disk images are grown to the specified size when they’re booted with mkosi boot or mkosi 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.
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 image with mkosi qemu, mkosi boot or mkosi shell.

Note that using this feature with mkosi qemu requires systemd v254 or newer in the guest.

Takes one of user, interface or none. Defaults to user. Specifies the networking to set up when booting the image. user sets up usermode networking. interface sets up a virtual network connection between the host and the image. This translates to a veth interface for mkosi shell and mkosi boot and a tap interface for mkosi qemu and mkosi vmspawn.

Note that when using interface, mkosi does not automatically configure the host interface. It is expected that a recent version of systemd-networkd is running on the host which will automatically configure the host interface of the link.

Mount the build sources configured with BuildSources= and the build directory (if one is configured) to the same locations in /work that they were mounted to when running the build script when using mkosi boot or mkosi qemu.
Configure systemd unit properties to add to the systemd scopes allocated when using mkosi boot or mkosi qemu. These are passed directly to the --property options of systemd-nspawn and systemd-run respectively.
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.
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.
Specify the machine name to use when booting the image. Can also be used to refer to a specific image when SSH-ing into an image (e.g. mkosi --image=myimage ssh).

Note that Ephemeral= has to be enabled to start multiple instances of the same image.

Specify the path to which journal logs from containers and virtual machines should be forwarded. If the path has the .journal extension, it is interpreted as a file to which the journal should be written. Otherwise, the path is interpreted as a directory to which the journal should be written.

Note that systemd v256 or newer is required in the virtual machine for log forwarding to work.

Note that if a path with the .journal extension is given, the journal size is limited to 4G. Configure an output directory instead of file if your workload produces more than 4G worth of journal data.

Matches against the configured profile.
Matches against the configured distribution.
Matches against the configured distribution release. If this condition is used and no distribution has been explicitly configured yet, the host distribution and release are used.
Matches against the configured architecture. If this condition is used and no architecture has been explicitly configured yet, the host architecture is used.
Matches against repositories enabled with the Repositories= setting. Takes a single repository name.
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.
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.
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 specification. 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.
Matches against the configured value for the Bootable= feature. Takes a boolean value or auto.
Matches against the configured value for the Format= option. Takes an output format (see the Format= option).
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.
Takes a build source target path (see BuildSources=). This match is satisfied if any of the configured build sources uses this target path. For example, if we have a mkosi.conf file containing:
[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 directory.

Matches against the host’s native architecture. See the Architecture= setting for a list of possible values.
Matches against the configured tools tree distribution.
Matches against a specific key/value pair configured with Environment=. If no value is provided, check if the given key is in the environment regardless of which value it has.

This table shows which matchers support globs, rich comparisons and the default value that is matched against if no value has been configured at the time the config file is read:

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
ToolsTreeDistribution= no no match default tools tree distribution
Environment= no no n/a

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 extra configuration from the given file or directory. The extra configuration is included immediately after parsing the setting, except when used on the command line, in which case the extra configuration is included after parsing all command line arguments.

Note that each path containing extra configuration is only parsed once, even if included more than once with Include=.

The builtin configs for the mkosi default initrd and default tools tree can be included by including the literal value mkosi-initrd and mkosi-tools respectively.

Note: Include names starting with either of the literals mkosi- or contrib- are reserved for use by mkosi itself.

Same as Include=, but the extra configuration files or directories are included when building the default initrd.
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.

When this setting is specified for the “main” image, it specifies which subimages should be built. See the Building multiple images section for more information.

The minimum mkosi version required to build this configuration. If specified multiple times, the highest specified version is used.
Takes a comma-separated list of paths to executables that are used as the configure scripts for this image. See the Scripts section for more information.
Takes a list of environment variable names separated by spaces. When building multiple images, pass the listed environment variables to each individual subimage as if they were “universal” settings. See the Building multiple images section for more information.

The current value of various settings can be accessed when parsing configuration files by using specifiers. 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
Profile= %p

There are also specifiers that are independent of settings:

Specifier Value
%C Parent directory of current config file
%P Current working directory
%D Directory that mkosi was invoked in

Finally, there are specifiers that are derived from a setting:

Specifier Value
%F The default filesystem of the configured distribution

Note that the current working directory changes as mkosi parses its configuration. Specifically, each time mkosi parses a directory containing a mkosi.conf file, mkosi changes its working directory to that directory.

Note that the directory that mkosi was invoked in is influenced by the --directory= command line argument.

The following table shows example values for the directory specifiers listed above:

$D/mkosi.conf $D/mkosi.conf.d/abc/abc.conf $D/mkosi.conf.d/abc/mkosi.conf
%C $D $D/mkosi.conf.d $D/mkosi.conf.d/abc
%P $D $D $D/mkosi.conf.d/abc
%D $D $D $D

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
•
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 distribution, 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 for mkosi build. Default values/calls are shown in parentheses. When building with --incremental 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.
Run configure scripts (mkosi.configure)
4.
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.
5.
Unshare the mount namespace
6.
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.
Sync the package manager repository metadata
3.
Run sync scripts (mkosi.sync)
4.
Copy base trees (--base-tree=) into the image
5.
Reuse a cached image if one is available
6.
Copy a snapshot of the package manager repository metadata into the image
7.
Copy skeleton trees (mkosi.skeleton) into image
8.
Install distribution and packages into image
9.
Run prepare scripts on image with the final argument (mkosi.prepare)
10.
Install build packages in overlay if any build scripts are configured
11.
Run prepare scripts on overlay with the build argument if any build scripts are configured (mkosi.prepare)
12.
Cache the image if configured (--incremental)
13.
Run build scripts on image + overlay if any build scripts are configured (mkosi.build)
14.
Finalize the build if the output format none is configured
15.
Copy the build scripts outputs into the image
16.
Copy the extra trees into the image (mkosi.extra)
17.
Run post-install scripts (mkosi.postinst)
18.
Write config files required for Ssh=, Autologin= and MakeInitrd=
19.
Install systemd-boot and configure secure boot if configured (--secure-boot)
20.
Run systemd-sysusers
21.
Run systemd-tmpfiles
22.
Run systemctl preset-all
23.
Run depmod
24.
Run systemd-firstboot
25.
Run systemd-hwdb
26.
Remove packages and files (RemovePackages=, RemoveFiles=)
27.
Run SELinux relabel is a SELinux policy is installed
28.
Run finalize scripts (mkosi.finalize)
29.
Generate unified kernel image if configured to do so
30.
Generate final output format
31.
Run post-output scripts (mkosi.postoutput)

To allow for image customization that cannot be implemented using mkosi’s builtin features, mkosi supports 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 namespace 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.configure (ConfigureScripts=) exists, it is executed before building the image. This script may be used to dynamically modify the configuration. It receives the configuration serialized as JSON on stdin and should output the modified configuration serialized as JSON on stdout. Note that this script only runs when building or booting the image (build, qemu, boot and shell verbs). If a default tools tree is configured, it will be built before running the configure scripts and the configure scripts will run with the tools tree available. This also means that the modifications made by configure scripts will not be visible in the summary output.
•
If mkosi.sync (SyncScripts=) exists, it is executed before the image is built. This script may be used to update various sources that are used to build the image. One use case is to run git pull on various source repositories before building the image. Specifically, the BuildSourcesEphemeral= setting does not apply to sync scripts, which means sync scripts can be used to update build sources even if BuildSourcesEphemeral= is enabled.
•
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 image’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 mkosi.postoutput (PostOutputScripts=) exists, it is executed right after all the output files have been generated, before they are finally moved into the output directory. This can be used to generate additional or alternative outputs, e.g. SHA256FILES or SBOM manifests.
•
If mkosi.clean (CleanScripts=) exists, it is executed right after the outputs of a previous build have been cleaned up. A clean script can clean up any outputs that mkosi does not know about (e.g. artifacts from SplitArtifacts=yes or RPMs built in a build script). Note that this script does not use the tools tree even if one is configured.

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.
•
$QEMU_ARCHITECTURE contains the architecture from $ARCHITECTURE in the format used by qemu. Useful for finding the qemu binary ( qemu-system-$QEMU_ARCHITECTURE).
•
$DISTRIBUTION contains the distribution from the Distribution= setting.
•
$RELEASE contains the release from the Release= setting.
•
$DISTRIBUTION_ARCHITECTURE contains the architecture from $ARCHITECTURE in the format used by the configured distribution.
•
$PROFILE contains the profile from the Profile= setting.
•
$CACHED= is set to 1 if a cached image is available, 0 otherwise.
•
$CHROOT_SCRIPT contains the path to the running script relative to the image root directory. The primary 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 previous 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.
•
$ARTIFACTDIR points to the directory that is used to pass around build artifacts generated during the build and make them available for use by mkosi. This is similar to PACKAGEDIR, but is meant for artifacts that may not be packages understood by the package manager, e.g. initrds created by other initrd generators than mkosi. Build scripts can add more artifacts to the directory by placing them in $ARTIFACTDIR. Files in this directory are only available for the current build and are not copied out like the contents of $OUTPUTDIR.

mkosi will also use certain subdirectories of an artifacts directory to automatically use their contents at certain steps. Currently the following two subdirectories in the artifact directory are used by mkosi:

•
io.mkosi.microcode: All files in this directory are used as microcode files, i.e. they are prepended to the initrds in lexicographical order.
•
io.mkosi.initrd: All files in this directory are used as initrds and joined in lexicographical order.

It is recommend users of $ARTIFACTDIR put things for their own use in a similar namespaced directory, e.h. local.my.namespace.

•
$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 executed (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, Environment=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>)
•
$MKOSI_CONFIG is a file containing a json summary of the settings of the current image. This file can be parsed inside scripts to gain access to all settings for the current image.
•
$IMAGE_ID contains the identifier from the ImageId= or --image-id= setting.
•
$IMAGE_VERSION contains the version from the ImageVersion= or --image-version= setting

Consult this table for which script receives which environment variables:

Variable configure sync prepare build postinst finalize postoutput clean
ARCHITECTURE ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
QEMU_ARCHITECTURE ✓
DISTRIBUTION ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
DISTRIBUTION_ARCHITECTURE ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
RELEASE ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
PROFILE ✓ ✓ ✓ ✓ ✓ ✓ ✓
CACHED ✓
CHROOT_SCRIPT ✓ ✓ ✓ ✓
SRCDIR ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
CHROOT_SRCDIR ✓ ✓ ✓ ✓
BUILDDIR ✓ ✓ ✓ ✓
CHROOT_BUILDDIR ✓
DESTDIR ✓
CHROOT_DESTDIR ✓
OUTPUTDIR ✓ ✓ ✓ ✓ ✓
CHROOT_OUTPUTDIR ✓ ✓ ✓
BUILDROOT ✓ ✓ ✓ ✓
PACKAGEDIR ✓ ✓ ✓ ✓
ARTIFACTDIR ✓ ✓ ✓ ✓
WITH_DOCS ✓ ✓
WITH_TESTS ✓ ✓
WITH_NETWORK ✓ ✓ ✓ ✓
SOURCE_DATE_EPOCH ✓ ✓ ✓ ✓ ✓
MKOSI_UID ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
MKOSI_GID ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
MKOSI_CONFIG ✓ ✓ ✓ ✓ ✓ ✓ ✓
IMAGE_ID ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
IMAGE_VERSION ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

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 chrooting 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 (dnf, rpm, apt, dpkg, 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.

Additionally, mkosi-install, mkosi-reinstall, mkosi-upgrade and mkosi-remove will invoke the corresponding operation of the package manager being used to built 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 image.

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.

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 creation of files that need to be provided early, for example to configure the package manager or set systemd 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.pkgmngr/ directory or mkosi.pkgmngr.tar archive may be used to configure the package manager without the files being inserted into the image. If the files should be included in the image mkosi.skeleton/ and mkosi.skeleton.tar should be used instead.

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 additional 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 password is prefixed with hashed: it is treated as an already hashed root password. The password may optionally 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 cryptsetup 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 RepartDirectories= 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.

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 configured 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 downloaded, 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 managers, 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.

If the mkosi.images/ directory exists, mkosi will load individual subimage 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 images specified in the Dependencies= setting of the main image and all of their dependencies (or all of them if no images were explicitly configured using Dependencies= in the main image configuration). To add dependencies between subimages, the Dependencies= setting can be used as well. Subimages are always built before the main image.

When images are defined, mkosi will first read the main image configuration (configuration outside of the mkosi.images/ directory), followed by the image specific configuration. Several “universal” settings apply to the main image and all its subimages and cannot be configured separately in subimages. The following settings are universal and cannot be configured in subimages (except for settings which take a collection of values which can be extended in subimages but not overridden):

•
Profile=
•
Distribution=
•
Release=
•
Architecture=
•
Mirror=
•
LocalMirror=
•
RepositoryKeyCheck=
•
Repositories=
•
CacheOnly=
•
PackageManagerTrees=
•
OutputDirectory=
•
WorkspaceDirectory=
•
CacheDirectory=
•
PackageCacheDirectory=
•
BuildDirectory=
•
ImageId=
•
ImageVersion=
•
SectorSize=
•
RepartOffline=
•
UseSubvolumes=
•
PackageDirectories=
•
VolatilePackageDirectories=
•
SourceDateEpoch=
•
BuildSources=
•
BuildSourcesEphemeral=
•
WithTests
•
WithNetwork=
•
VerityKey=
•
VerityKeySource=
•
VerityCertificate=
•
ProxyUrl=
•
ProxyExclude=
•
ProxyPeerCertificate=
•
ProxyClientCertificate=
•
ProxyClientKey=
•
Incremental=
•
ExtraSearchPaths=
•
Acl=
•
ToolsTree=
•
ToolsTreeCertificates=

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/systemd/systemd/tree/main/mkosi.images) repository.

•
$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.
•
$EPEL_MIRROR can be used to override the default mirror location used for the epel repositories when Mirror= is used. By default mkosi looks for the epel repositories in the fedora subdirectory of the parent directory of the mirror specified in Mirror=. For example if the mirror is set to https://mirror.net/centos-stream mkosi will look for the epel repositories in https://mirror.net/fedora/epel.

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

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 kernel, 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. Alternatively the machine can be shut down using Ctrl-a x.

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 commandline 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 systemd-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.

mkosi is packaged for various distributions: Debian, Ubuntu, Arch Linux, Fedora Linux, OpenMandriva, Gentoo. 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 debian-archive-keyring packages explicitly, in addition to apt, depending on what kind of distribution images you want to build.

Note that the minimum required Python version is 3.9.

•
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-permissions.conf to /etc/tmpfiles.d/static-nodes-permissions.conf and change the mode of /dev/kvm from 0660 to 0666.

•
How do I add a regular user to an image?

You can use the following snippet in a post-installation script:

useradd --create-home --user-group $USER --password "$(openssl passwd -stdin -6 <$USER_PASSWORD_FILE)"

Note that from systemd v256 onwards, if enabled, systemd-homed-firstboot.service will prompt to create a regular user on first boot if there are no regular users.

•
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-images.html) introductory blog post by Lennart Poettering
•
The mkosi OS generation tool (https://lwn.net/Articles/726655/) story on LWN

systemd-nspawn(1), dnf(8)