mkosi [options...] build
mkosi [options...] clean
mkosi [options...] summary
mkosi [options...] shell [command line...]
mkosi [options...] boot [nspawn settings...]
mkosi [options...] qemu
mkosi is a tool for easily building legacy-free OS images. It’s a fancy wrapper around
zypper that may generate disk images with a number of bells and whistles.
Supported output formats
The following output formats are supported:
- Raw GPT disk image, with ext4 as root (gpt_ext4)
- Raw GPT disk image, with xfs as root (gpt_xfs)
- Raw GPT disk image, with btrfs as root (gpt_btrfs)
- Raw GPT disk image, with squashfs as read-only root (gpt_squashfs)
- Plain squashfs image, without partition table, as read-only root (plain_squashfs)
- Plain directory, containing the OS tree (directory)
- btrfs subvolume, with separate subvolumes for
- Tarball (tar)
When a GPT disk image is created, the following additional options are available:
- A swap partition may be added in
- The image may be made bootable on EFI and BIOS systems
- Separate partitions for
/homemay be added in
- The root, /srv and /home partitions may optionally be encrypted with LUKS.
- A dm-verity partition may be added in that adds runtime integrity data for the root partition
- Optionally, create an SHA256SUMS checksum file for the result, possibly even signed via
- Optionally, place a specific
.nspawnsettings file along with the result.
- Optionally, build a local project’s source tree in the image and add the result to the generated image (see below).
- Optionally, share RPM/DEB package cache between multiple runs, in order to optimize build speeds.
- Optionally, the resulting image may be compressed with XZ.
- Optionally, the resulting image may be converted into a QCOW2 file suitable for
- Optionally, btrfs’ read-only flag for the root subvolume may be set.
- Optionally, btrfs’ compression may be enabled for all created subvolumes.
- By default images are created without all files marked as documentation in the packages, on distributions where the package manager supports this. Use the
--with-docsflag to build an image with docs added.
Command Line Verbs
The following command line verbs are known:
This builds the image, based on the settings passed in on the command line or read from a
mkosi.defaultfile, see below. This verb is the default if no verb is explicitly specified. This command must be executed as
Remove build artifacts generated on a previous build. If combined with
-f, also removes incremental build cache images. If
-fis specified twice, also removes any package cache.
Outputs a human-readable summary of all options used for building an image. This will parse the command line and
mkosi.defaultfile as it would do on
build, but only output what it is configured for and not actually build anything.`
This builds the image if it is not build yet, and then invokes
systemd-nspawnto acquire an interactive shell prompt in it. If this verb is used an optional command line may be specified which is then invoked in place of the shell in the container. Combine this with
-fin order to rebuild the image unconditionally before acquiring the shell, see below. This command must be executed as
shellbut boots the image up using
systemd-nspawn. If this verb is used an optional command line may be specified which is passed as “kernel command line” to the init system in the image.
qemuto boot up the image, i.e. instead of container virtualization VM virtualization is used. This verb is only supported on images that contain a boot loader, i.e. those built with
--bootable(see below). This command must be executed as
rootunless the image already exists and
-fis not specified.
When the image is built with the
--sshoption, this command connects to a booted (
qemuverbs) container/VM via SSH. Make sure to run
mkosi sshwith the same config as
mkosi buildwas run with so that it has the necessary information available to connect to the running container/VM via SSH.
This verb is equivalent to the
--helpswitch documented below: it shows a brief usage explanation.
Command Line Parameters
The following command line parameters are understood. Note that many of these parameters can also be set in the
mkosi.default file, for details see the table below.
- --distribution=, -d
The distribution to install in the image. Takes one of the following arguments:
openmandriva. If not specified, defaults to the distribution of the host.
- --release=, -r
The release of the distribution to install in the image. The precise syntax of the argument this takes depends on the distribution used, and is either a numeric string (in case of Fedora, CentOS, ..., e.g.
29), or a distribution version name (in case of Debian, Ubuntu, ..., e.g.
artful). If neither this option, not
--distribution=is specified, defaults to the distribution version of the host. If the distribution is specified, defaults to a recent version of it.
- --mirror=, -m
The mirror to use for downloading the distribution packages. Expects a mirror URL as argument.
Additional package repositories to use during installation. Expects one or more URLs as argument, separated by commas. This option may be used multiple times, in which case the list of repositories to use is combined. Use “!*” to remove all repositories from to the list or use e.g. “!repo-url” to remove just one specific repository. For Arch Linux, additional repositories must be passed in the form
The architecture to build the image for. Note that this currently only works for architectures compatible with the host’s architecture.
- --format=, -t
The image format type to generate. One of
directory(for generating OS images inside a local directory),
subvolume(similar, but as a btrfs subvolume),
tar(similar, but a tarball of the image is generated),
gpt_ext4(a block device image with an ext4 file system inside a GPT partition table),
gpt_xfs(similar, but with an xfs file system),
gpt_btrfs(similar, but with an btrfs file system),
gpt_squashfs(similar, but with a squashfs file system),
plain_squashfs(a plain squashfs file system without a partition table).
- --output=, -o
Path for the output image file to generate. Takes a relative or absolute path where the generated image will be placed. If neither this option nor
--output-dir=is used (see below), the image is generated under the name
image, but its name suffixed with an appropriate file suffix (e.g.
gpt_ext4is used in combination with
- --output-dir=, -O
Path to a directory where to place all generated artifacts (i.e. the
SHA256SUMSfile and similar). If this is not specified and a directory
mkosi.output/exists in the local directory it is automatically used for this purpose. If this is not specified and such a directory does not exist, all output artifacts are placed adjacent to the output image file.
- --force, -f
Replace the output file if it already exists, when building an image. By default when building an image and an output artifact already exists
mkosiwill refuse operation. Specify
-fto delete all build artifacts from a previous run before re-building the image. If incremental builds are enabled (see below), 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 (see below), specifying this option thrice will ensure the package cache is removed too, before the re-build is initiated. For the
-fhas 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.
Override the first usable LBA (Logical Block Address) within the GPT header. This defaults to
2048which is actually the desired value. However, some tools, e.g. the
prl_disk_toolutility from the Parallels virtualization suite require this to be set to
34, otherwise they might fail to resize the disk image and/or partitions inside it.
- --bootable, -b
Generate a bootable image. By default this will generate an image bootable on UEFI systems. Use
--boot-protocols=to select support for a different boot protocol.
Pick one or more boot protocols to support when generating a bootable image, as enabled with
--bootableabove. Takes a comma-separated list of
bios. May be specified more than once in which case the specified lists are merged. If
uefiis specified the
sd-bootUEFI boot loader is used, if
biosis specified the GNU Grub boot loader is used. Use “!*” to remove all previously added protocols or “!protocol” to remove one protocol.
Use the specified kernel command line when building bootable images. By default command line arguments get appended. To remove all arguments from the current list pass “!*”. To remove specific arguments add a space separated list of “!” prefixed arguments. For example adding “!* console=ttyS0 rw” to a mkosi.default file or the command line arguments passes “console=ttyS0 rw” to the kernel in any case. Just adding “console=ttyS0 rw” would append these two arguments to the kernel command line created by lower priority configuration files or previous –kernel-command-line command line arguments.
Sign the resulting kernel/initrd image for UEFI SecureBoot
Path to the PEM file containing the secret key for signing the UEFI kernel image, if
Path to the X.509 file containing the certificate for the signed UEFI kernel image, if
Make root file system read-only. Only applies to
subvolumeoutput formats, and implied on
Attempt to make the resulting root file system as small as possible by removing free space from the file system. Only supported for
gpt_btrfs. For ext4 this relies on
resize2fs -M, which reduces the free disk space but is not perfect and generally leaves some free space. For btrfs the results are optimal and no free space is left.
Encrypt all partitions in the file system or just the root file system. Takes either
dataas argument. If
/srvfile systems will be encrypted using dm-crypt/LUKS (with its default settings). If
datathe root file system will be left unencrypted, but
/srvwill be encrypted. The passphrase to use is read from the
mkosi.passphrasefile in the current working directory (see below). Note that the UEFI System Partition (ESP) containing the boot loader and kernel to boot is never encrypted since it needs to be accessible by the firmware.
Add an “Verity” integrity partition to the image. If enabled, the root partition is protected with
dm-verityagainst off-line modification, the verification data is placed in an additional GPT partition. Implies
Compress the generated file systems. Only applies to
plain_squashfs. Takes one of
xzor a boolean value as argument. If the latter is used compression is enabled/disabled and the default algorithm is used. In case of the
squashfsoutput formats compression is implied, however this option may be used to select the algorithm.
Set the path to the
mksquashfsexecutable to use. This is useful in case the parameters for the tool shall be augmented, as the tool may be replaced by a script invoking it with the right parameters, this way.
Compress the resulting image with
xz. This only applies to
gpt_squashfsand is implied for
tar. Note that when applied to the block device image types this means the image cannot be started directly but needs to be decompressed first. This also means that the
qemuverbs are not available when this option is used.
Encode the resulting image as QEMU QCOW2 image. This only applies to
gpt_squashfs. QCOW2 images can be read natively by
qemu, but not by the Linux kernel. This means the
bootverbs are not available when this option is used, however
Set the image’s hostname to the specified name.
If specified, mkosi does not build unified kernel images and instead installs kernels with a separate initrd and boot loader config to the efi or bootloader partition.
If specified, mkosi will run the tool to create the initrd such that a non-generic initrd is created that will only be able to run on the system mkosi is run on. Currently mkosi uses dracut for all supported distributions except Clear Linux and this option translates to enabling dracut’s hostonly option.
By default, if
mkosiis run inside a
sudoenvironment all generated artifacts have their UNIX user/group ownership changed to the user which invoked
sudo. With this option this may be turned off and all generated files are owned by
If running on a SELinux-enabled system (Fedora, CentOS), files inside the container are tagged with SELinux context extended attributes (
xattrs), which may interfere with host SELinux rules in building or further container import stages. This option strips SELinux context attributes from the resulting tar archive.
- --incremental, -i
Enable incremental build mode. This only applies if the two-phase
mkosi.buildbuild script logic is used. In this mode, a copy of the OS image is created immediately after all OS packages are unpacked but before the
mkosi.buildscript is invoked in the development container. Similar a copy of the final image is created immediately before the build artifacts from the
mkosi.buildscript are copied in. On subsequent invocations of
-iswitch these cached images may be used to skip the OS package unpacking, thus drastically speeding up repetitive build times. Note that when this is used and a pair of cached incremental images exists they are not automatically regenerated, even if options such as
--packages=are modified. In order to force rebuilding of these cached images, combined
-ff, which ensures the cached images are removed first, and then re-created.
- --package=, -p
Install the specified distribution packages (i.e. RPM, DEB, ...) in the image. Takes a comma separated list of packages. This option may be used multiple times in which case the specified package list is combined. Packaged specified this way will be installed both in the development and the final image (see below). Use
--build-package=(see below) to specify packages that shall only be used for the image generated in the build image, but that shall not appear in the final image. To remove a package e.g. added by a mkosi.default configuration file prepend the package name with a ! letter. For example -p “!apache2” would remove the apache2 package. To replace the apache2 package by the httpd package just add -p “!apache2,httpd” to the command line arguments. To remove all packages use “!*”.
Include documentation in the image built. By default if the underlying distribution package manager supports it documentation is not included in the image built. The
$WITH_DOCSenvironment variable passed to the
mkosi.buildscript indicates whether this option was used or not, see below.
- --without-tests, -T
If set the
$WITH_TESTSenvironment variable is set to
mkosi.buildscript is invoked. This is supposed to be used by the build script 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.buildbuild script honors it.
Takes a path to a directory to use as package cache for the distribution package manager used. If this option is not used, but a
mkosi.cache/directory is found in the local directory it is automatically used for this purpose (also see below). The directory configured this way is mounted into both the development and the final image while the package manager is running.
Takes a path to a directory to copy on top of the OS tree the package manager generated. Use this to override any default configuration files shipped with the distribution. If this option is not used, but the
mkosi.extra/directory is found in the local directory it is automatically used for this purpose (also see below). Instead of a directory a
tarfile may be specified too. In this case it is unpacked into the OS tree before the package manager is invoked. This mode of operation allows setting permissions and file ownership explicitly, in particular for projects stored in a version control system such as
gitwhich does retain full file ownership and access mode metadata for committed files. If a tar file
mkosi.extra.taris found in the local directory it automatically used for this purpose.
Takes a path to a directory to copy into the OS tree before invoking the package manager. Use this to insert files and directories into the OS tree before the package manager installs any packages. If this option is not used, but the
mkosi.skeleton/directory is found in the local directory it is automatically used for this purpose (also see below). As with the extra tree logic above, instead of a directory a
tarfile may be used too, and
mkosi.skeleton.taris automatically used.
Takes a path to an executable that is used as build script for this image. If this option is used the build process will be two-phased instead of single-phased (see below). The specified script is copied onto the development image and executed inside an
systemd-nspawncontainer environment. If this option is not used, but the
mkosi.buildfile found in the local directory it is automatically used for this purpose (also see below).
Takes a path of a source tree to copy into the development image, if a build script is used. This only applies if a build script is used, and defaults to the local directory. Use
--source-file-transfer=to configure how the files are transferred from the host to the container image.
Takes a path of a directory to use as 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. This directory is mounted into the development image when the build script is invoked. The build script can find the path to this directory in the
$BUILDDIRenvironment variable. 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 below).
Takes a path of a directory to use as the include directory. This directory is mounted at /usr/include when building the build image and when running the build script. This means all include files installed to /usr/include will be stored in this directory. This is useful to make include files available on the host system for use by language servers to provide code completion. If this option is not specified, but a directory
mkosi.includedir/exists in the local directory, it is automatically used for this purpose (also see below).
Takes a path of a directory to use as the install directory. The directory used this way is shared between builds and allows the build system to not have to reinstall files that were already installed by a previous build and didn’t change. The build script can find the path to this directory in the
$DESTDIRenvironment variable. If this option is not specified, but a directory
mkosi.installdirexists in the local directory, it is automatically used for this purpose (also see below).
--package=, but configures packages to install only in the first phase of the build, into the development image. This option should be used to list packages containing header files, compilers, build systems, linkers and other build tools the
mkosi.buildscript requires to operate. Note that packages listed here are only included in the image created during the first phase of the build, and are absent in the final image. use
--package=to list packages that shall be included in both. Packages are appended to the list. Packages prefixed with “!” are removed from the list. “!*” removes all packages from the list.
Causes the (second) final image build stage to be skipped. This is useful in combination with a build script, for when you care about the artifacts that were created locally in
$BUILDDIR, but ultimately plan to discard the final image.
Takes a path to an executable that is invoked inside the image right after installing the software packages. It is the last step before the image is cached (if incremental mode is enabled). This script is invoked inside a
systemd-nspawncontainer environment, and thus does not have access to host resources. If this option is not used, but an executable script
mkosi.prepareis found in the local directory, it is automatically used for this purpose (also see below).
Takes a path to an executable that is invoked inside the final image right after copying in the build artifacts generated in the first phase of the build. This script is invoked inside a
systemd-nspawncontainer environment, and thus does not have access to host resources. If this option is not used, but an executable
mkosi.postinstis found in the local directory, it is automatically used for this purpose (also see below).
Takes a path to an executable that is invoked outside the final image right after copying in the build artifacts generated in the first phase of the build, and after having executed the
mkosi.postinstscript (see above). This script is invoked directly in the host environment, and hence has full access to the host’s resources. If this option is not used, but an executable
mkosi.finalizeis found in the local directory, it is automatically used for this purpose (also see below).
Configures how the source file tree (as configured with
--build-sources=) is transferred into the container image during the first phase of the build. Takes one of
copy-all(to copy all files from the source tree),
copy-git-cached(to copy only those files
copy-git-others(to copy only those files
mountto bind mount the source tree directly. Defaults to
gitsource tree is detected, otherwise
copy-all. When you specify
copy-git-more, it is the same as
copy-git-cached, except it also includes the
--source-file-transferbut for the final image instead of the build image. Takes the same values as
mount. By default, sources are not copied into the final image.
Enables network connectivity while the build script
mkosi.buildis invoked. By default, the build script runs with networking turned off. The
$WITH_NETWORKenvironment variable is passed to the
mkosi.buildbuild script indicating whether the build is done with or without this option. If specified as
--with-network=neverthe package manager is instructed not to contact the network for updating package data. This provides a minimal level of reproducibility, as long as the package data cache is already fully populated.
.nspawnsettings file for
systemd-nspawnto use in the
shellverbs, and to place next to the generated image file. This is useful to configure the
systemd-nspawnenvironment when the image is run. If this setting is not used but an
mkosi.nspawnfile found in the local directory it is automatically used for this purpose (also see below).
Takes a size in bytes for the root file system. The specified numeric value may be suffixed with
Gto indicate kilo-, mega- and gigabytes (all to the base of 1024). This applies to output formats
gpt_btrfs. Defaults to 1G, except for
gpt_xfswhere it defaults to 1.3G.
Similar, and configures the size of the UEFI System Partition (ESP). This is only relevant if the
--bootableoption is used to generate a bootable image. Defaults to 256M.
Similar, and configures the size of a swap partition on the image. If omitted no swap partition is created.
Similar, and configures the size of the
/homepartition. If omitted no separate
/homepartition is created.
Similar, and configures the size of the
/srvpartition. If omitted no separate
/srvpartition is created.
SHA256SUMSfile of all generated artifacts after the build is complete.
Sign the generated
gpgkey to use for signing
SHA256SUMS. This key is required to exist in the
bmapfile for usage with
bmaptoolfrom the generated image file.
Set the password of the
rootuser. By default the
rootaccount is locked. If this option is not used but a file
mkosi.rootpwexists in the local directory the root password is automatically read from it.
Indicate that the password supplied for the
rootuser has already been hashed, so that the string supplied with
mkosi.rootpwwill be written to
Enable autologin for the
rootuser on pts/0 (nspawn), tty1 (QEMU) and ttyS0 (QEMU with –qemu-headless) by patching /etc/pam.d/login.
List of colon-separated paths to look for tools in, before using the regular
- --directory=, -C
Takes a path to a directory.
mkosiswitches to this directory before doing anything. Note that the various
mkosi.*files are searched for only after changing to this directory, hence using this option is an effective way to build a project located in a specific directory.
Loads additional settings from the specified settings file. Most command line options may also be configured in a settings file. See the table below to see which command line options match which settings file option. If this option is not used, but a file
mkosi.defaultis found in the local directory it is automatically used for this purpose. If a setting is configured both on the command line and in the settings file, the command line generally wins, except for options taking lists in which case both lists are combined.
- --all, -a
Iterate through all files
mkosi.files/subdirectory, and build each as if
--default=mkosi.files/mkosi....was invoked. This is a quick way to build a large number of images in one go. Any additional specified command line arguments override the relevant options in all files processed this way.
If specified, overrides the directory the
--alllogic described above looks for settings files in. If unspecified, defaults to
mkosi.files/in the current working directory (see above).
Show package version.
- --help, -h
Show brief usage information.
When used with the build verb, this option adds
console=ttyS0to the image’s kernel command line and sets the terminal type of the serial console in the image to the terminal type of the host (more specifically, the value of the TERM environment variable passed to mkosi). This makes sure that all terminal features such as colors and shortcuts still work as expected when connecting to the qemu VM over the serial console (for example via
When used with the qemu verb, this option adds the
-nographic option to qemu’s command line so qemu starts a headless vm and connects to its serial console from the current terminal instead of launching the VM in a separate window.
When used with the boot or qemu verbs, this option creates a virtual ethernet link between the host and the container/VM. The host interface is automatically picked up by systemd-networkd as documented in systemd-nspawn’s man page: https://www.freedesktop.org/software/systemd/man/systemd-nspawn.html#-n
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 subvolume snapshots or `reflinks' natively (“btrfs” or new “xfs”) than on more traditional file systems that do not (“ext4”).
If specified, installs and enables sshd in the final image and generates a SSH keypair and adds the public key to root’s authorized keys in the final image. The private key is stored in mkosi’s output directory. When building with this option and running the image using
mkosi qemu, the
mkosi sshcommand can be used to connect to the container/VM via SSH.
Command Line Parameters and their Settings File Counterparts
Most command line parameters may also be placed in an
mkosi.default settings file (or any other file
--default= is used on). The following table shows which command lines parameters correspond with which settings file options.
|Command Line Parameter|
Command line options that take no argument are not suffixed with a
= in their long version in the table above. In the
mkosi.default file they are modeled as boolean option that take either
true for enabling, and
false for disabling.
Images may be created containing installations of the following OSes.
- Arch Linux
- Clear Linux
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
debootstrap may be used to build Debian or Ubuntu images. Any distribution that packages
dnf may be used to build Fedora, Mageia or OpenMandriva images. Any distro that packages
pacstrap may be used to build Arch Linux images. Any distribution that packages
zypper may be used to build openSUSE images. Any distribution that packages
yum (or the newer replacement
dnf) may be used to build CentOS images.
Currently, Fedora packages all relevant tools as of Fedora 28.
Generated images are legacy-free. This means only GPT disk labels (and no MBR disk labels) are supported, and only systemd based images may be generated.
All generated GPT disk images may be booted in a local container directly with:
systemd-nspawn -bi image.raw
Additionally, bootable GPT disk images (as created with the
--bootable flag) work when booted directly by EFI and BIOS systems, for example in KVM via:
qemu-kvm -m 512 -smp 2 -bios /usr/share/edk2/ovmf/OVMF_CODE.fd -drive format=raw,file=image.raw
EFI bootable GPT images are larger than plain GPT images, as they additionally carry an EFI system partition containing a boot loader, as well as a kernel, kernel modules, udev and more.
All directory or btrfs subvolume images may be booted directly with:
systemd-nspawn -bD image
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:
mkosi.defaultmay be used to configure mkosi’s image building process. For example, you may configure the distribution to use (
openmandriva) for the image, or additional distribution packages to install. Note that all options encoded in this configuration file may also be set on the command line, and this file is hence little more than a way to make sure simply typing
mkosiwithout further parameters in your source tree is enough to get the right image of your choice set up. Additionally if a
mkosi.default.ddirectory exists, each file in it is loaded in the same manner adding/overriding the values specified in
mkosi.default.dcontains a directory named after the distribution being built, each file in that directory is also processed. The file format is inspired by Windows
.inifiles and supports multi-line assignments: any line with initial whitespace is considered a continuation line of the line before. Command-line arguments, as shown in the help description, have to be included in a configuration block (e.g. “[Packages]”) corresponding to the argument group (e.g. “Packages”), and the argument gets converted as follows: “–with-network” becomes “WithNetwork=yes”. For further details see the table above.
mkosi.extra.tarmay be respectively a directory or archive. If any exist all files contained in it are copied over the directory tree of the image after the OS was installed. This may be used to add in additional files to an image, on top of what the distribution includes in its packages. When using a directory file ownership is not preserved: all files copied will be owned by root. To preserve ownership use a tar archive.
mkosi.skeleton.tarmay be respectively a directory or archive, and they work in the same way as
mkosi.skeleton.tar. However the files are copied before anything else so to have a skeleton tree for the OS. This allows to change the package manager and create files that need to be there before anything is installed. When using a directory file ownership is not preserved: all files copied will be owned by root. To preserve ownership use a tar archive.
mkosi.buildmay be an executable script. If it exists the image will be built twice: the first iteration will be the development image, the second iteration will be the final image. The development image is used to build the project in the current working directory (the source tree). For that the whole directory is copied into the image, along with the mkosi.build build script. The script is then invoked inside the image (via
$SRCDIRpointing to the source tree.
$DESTDIRpoints to a directory where the script should place any files generated it would like to end up in the final image. Note that
mesonbased build systems generally honor
$DESTDIR, thus making it very natural to build source trees from the build script. After the development image was built and the build script ran inside of it, it is removed again. After that the final image is built, without any source tree or build script copied in. However, this time the contents of
$DESTDIRare added into the image.
When the source tree is copied into the build image, all files are copied, except for
mkosi.output/. That said,
.gitignoreis respected if the source tree is a
gitcheckout. If multiple different images shall be built from the same source tree it’s essential to exclude their output files from this copy operation, as otherwise a version of an image built earlier might be included in a later build, which is usually not intended. An alternative to excluding these built images via
.gitignoreentries is making use of the
mkosi.output/directory (see below), which is an easy way to exclude all build artifacts.
MKOSI_DEFAULTenvironment variable will be set inside of this script so that you know which
mkosi.default(if any) was passed in.
mkosi.preparemay be an executable script. If it exists it is invoked directly after the software packages are installed, from within the image context. It is once called for the development image (if this is enabled, see above) with the “build” command line parameter, right before copying the extra tree. It is called a second time for the final image with the “final” command line parameter. 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). This script is executed within
$SRCDIR. In contrast to a general purpose installation, it is safe to install packages to the system (
npm install -g) instead of in
$SRCDIRitself 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.
mkosi.postinstmay be an executable script. If it exists it is invoked as the penultimate step of preparing an image, from within the image context. It is once called for the development image (if this is enabled, see above) with the “build” command line parameter, right before invoking the build script. It is called a second time for the final image with the “final” command line parameter, right before the image is considered complete. This script may be used to alter the images without any restrictions, after all software packages and built sources have been installed. Note that this script is executed directly in the image context with the final root directory in place, without any
mkosi.finalizemay be an executable script. If it exists it is invoked as last step of preparing an image, from the host system. It is once called for the development image (if this is enabled, see above) with the “build” command line parameter, as the last step before invoking the build script, after the
mkosi.postinstscript is invoked. It is called the second time with the “final” command line parameter as the last step before the image is considered complete. The environment variable
$BUILDROOTpoints to the root directory of the installation image. Additional verbs may be added in the future, the script should be prepared for that. This script may be used to alter the images without any restrictions, after all software packages and built sources have been installed. This script is more flexible than
mkosi.postinstin two regards: it has access to the host file system so it’s easier to copy in additional files or to modify the image based on external configuration, and the script is run in the host, so it can be used even without emulation even if the image has a foreign architecture.
mkosi.mksquashfs-toolmay be an executable script. If it exists is is called instead of
mkosi.nspawnmay be an nspawn settings file. If this exists it will be copied into the same place as the output image file. This is useful since nspawn looks for settings files next to image files it boots, for additional container runtime settings.
mkosi.cache/may be a directory. If so, it is automatically used as package download cache, in order to speed repeated runs of the tool.
mkosi.builddir/may be a directory. If so, it is automatically used as out-of-tree build directory, if the build commands in the
mkosi.buildscript support it. Specifically, this directory will be mounted into the build container, and the
$BUILDDIRenvironment variable will be set to it when the build script is invoked. The 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
mkosiis used in incremental mode (
-i): not only the disk images but also the build tree is reused between subsequent invocations. Note that if this directory does not exist the
$BUILDDIRenvironment variable is not set, and it is up to build script to decide whether to do in in-tree or an out-of-tree build, and which build directory to use.
mkosi.includedir/may be a directory. If so, it is automatically used as out-of-tree include directory. Specifically, this directory will be mounted into the build container at /usr/include when building the build image and when running the build script. After building the (cached) build image, this directory will contain all the files installed to /usr/include. Language servers or other tools can use these files to provide a better editing experience for developers working on a project.
mkosi.installdir/may be a directory. If so, it is automatically used as the install directory. Specifically, this directory will be mounted into the container at /root/dest when running the build script. After running the build script, the contents of this directory are installed into the final image. This is useful to cache the install step of the build. If used, subsequent builds will only have to reinstall files that have changed since the previous build.
mkosi.rootpwmay be a file containing the password or hashed password (if
--password-is-hashedis set) for the root user of the image to set. 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).
mkosi.passphrasemay be a passphrase file 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. If this file does not exist and encryption is requested the user is queried instead.
mkosi.secure-boot.keymay contain an X.509 certificate and PEM private key to use when UEFI SecureBoot support is enabled. All EFI binaries included in the image’s ESP are signed with this key, as a late step in the build process.
mkosi.output/may be a directory. If it exists, and the image output path is not configured (i.e. no
--output=setting specified), or configured to a filename (i.e. a path containing no
/character) all build artifacts (that is: the image itself, the root hash file in case Verity is used, the checksum and its signature if that’s enabled, and the nspawn settings file if there is any) are placed in this directory. Note that this directory is not used if the image output path contains at least one slash, and has no effect in that case. This setting is particularly useful if multiple different images shall be built from the same working directory, as otherwise the build result of a preceding run might be copied into a build image as part of the source tree (see above).
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.default, in case the default settings are not acceptable for a project.
If no build script
mkosi.build (see above) is used the build consists of a single phase only: the final image is generated as the combination of
mkosi.skeleton/ (see above), the unpacked distribution packages and
If a build script
mkosi.build is used the build consists of two phases: in the the first
development phase an image that includes necessary build tools (i.e. the combination of
BuildPackages= is installed) is generated (i.e. the combination of
mkosi.skeleton/ and unpacked distribution packages). Into this image the source tree is copied and
mkosi.build executed. The artifacts the
mkosi.build generates are saved. Then, the second
final phase starts: an image that excludes the build tools (i.e. only
Packages= is installed,
BuildPackages= is not) is generated. This time the build artifacts saved from the first phase are copied in, and
mkosi.extra copied on top, thus generating the final image.
The two-phased approach ensures that source tree is executed in a clean and comprehensive environment, while at the same the final image remains minimal and contains only those packages necessary at runtime, but avoiding those necessary at build-time.
Note that only the package cache
mkosi.cache/ (see below) is shared between the two phases. The distribution package manager is executed exactly once in each phase, always starting from a directory tree that is populated with
mkosi.skeleton but nothing else.
mkosi supports three different caches for speeding up repetitive re-building of images. Specifically:
- The package cache of the distribution package manager may be cached between builds. This is configured with the
--cache=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.
- If an
mkosi.buildscript is used, by enabling incremental build mode with
--incremental(see above) a cached copy of the development and final images can be made immediately before the build sources are copied in (for the development image) or the artifacts generated by
mkosi.buildare 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
- 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 the
The package cache (i.e. the first item above) is unconditionally useful. The latter two caches 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: an OS image rebuilt will be almost as quick to build the source tree only.
The build script
mkosi.build receives the following environment variables:
$SRCDIRcontains the path to the sources to build.
$DESTDIRis a directory into which any artifacts generated by the build script shall be placed.
$BUILDDIRis only defined if
mkosi.builddirand 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.
1depending on whether a build without or with installed documentation was requested (see
--with-docsabove). The build script should suppress installation of any package documentation to
$WITH_DOCSis set to
1depending on whether a build without or with running the test suite was requested (see
--without-testsabove). The build script should avoid running any unit or integration tests in case
1depending on whether a build without or with networking is being executed (see
--with-networkabove). The build script should avoid any network communication in case
Create and run a raw GPT image with ext4, as
# mkosi # systemd-nspawn -b -i image.raw
Create and run a bootable btrfs GPT image, as
# mkosi -t gpt_btrfs --bootable -o foobar.raw # systemd-nspawn -b -i foobar.raw # qemu-kvm -m 512 -smp 2 -bios /usr/share/edk2/ovmf/OVMF_CODE.fd -drive format=raw,file=foobar.raw
Create and run a Fedora image into a plain directory:
# mkosi -d fedora -t directory -o quux # systemd-nspawn -b -D quux
Create a compressed image
image.raw.xz and add a checksum file, and install SSH into it:
# mkosi -d fedora -t gpt_squashfs --checksum --xz --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.default <<EOF [Distribution] Distribution=fedora Release=24 [Output] Format=gpt_btrfs Bootable=yes [Packages] Packages=openssh-clients httpd BuildPackages=make gcc libcurl-devel EOF # cat > mkosi.build <<EOF #!/bin/sh cd $SRCDIR ./autogen.sh ./configure --prefix=/usr make -j `nproc` make install EOF # chmod +x mkosi.build # mkosi # systemd-nspawn -bi image.raw
To create a Fedora image with hostname:
# mkosi -d fedora --hostname image
Also you could set hostname in configuration file:
# cat mkosi.default ... [Output] Hostname=image ...
mkosi is packaged for various distributions: Debian, Ubuntu, Arch (in AUR), Fedora, OpenMandriva. It is usually easiest to use the distribution package.
The current version requires systemd 233 (or actually, systemd-nspawn of it).
When not using distribution packages make sure to install the necessary dependencies. For example, on Fedora you need:
dnf install arch-install-scripts btrfs-progs debootstrap dosfstools edk2-ovmf e2fsprogs squashfs-tools gnupg python3 tar veritysetup xfsprogs xz zypper sbsigntools
On Debian/Ubuntu it might be necessary to install the
debian-archive-keyring packages explicitly, in addition to
debootstrap, depending on what kind of distribution images you want to build.
debootstrap on Debian only pulls in the Debian keyring on its own, and the version on Ubuntu only the one from Ubuntu.
Note that the minimum required Python version is 3.6.
- Primary mkosi git repository on GitHub (https://github.com/systemd/mkosi/)
- mkosi — A Tool for Generating OS Images (http://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
The mkosi Authors.