# mkosi - Create legacy-free OS images
A fancy wrapper around `dnf --installroot`, `debootstrap`,
`pacstrap` and `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 (*raw_gpt*)
* Raw *GPT* disk image, with btrfs as root (*raw_btrfs*)
* Raw *GPT* disk image, with squashfs as read-only root (*raw_squashfs*)
* Plain directory, containing the *OS* tree (*directory*)
* btrfs subvolume, with separate subvolumes for `/var`, `/home`,
`/srv`, `/var/tmp` (*subvolume*)
* 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* systems
* Separate partitions for `/srv` and `/home` may be added in
* The root, /srv and /home partitions may optionally be encrypted with
* A dm-verity partition may be added in that adds runtime integrity
data for the root partition
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. Moreover, for bootable
images only *EFI* systems are supported (not plain *MBR/BIOS*).
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* 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
All directory or btrfs subvolume images may be booted directly
systemd-nspawn -bD image
# Other features
* Optionally, create an *SHA256SUMS* checksum file for the result,
possibly even signed via gpg.
* Optionally, place a specific `.nspawn` settings 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, btrfs' read-only flag for the root subvolume may be
* Optionally, btrfs' compression may be enabled for all
* 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-docs` flag to
build an image with docs added.
# Supported distributions
Images may be created containing installations of the
* *Arch Linux* (incomplete)
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 distro
that packages `debootstrap` may be used to build *Debian* or
*Ubuntu* images. Any distro that packages `dnf` may be used to
build *Fedora* images. Any distro that packages `pacstrap` may
be used to build *Arch Linux* images. Any distro that packages
`zypper` may be used to build *openSUSE* images.
Currently, *Fedora* packages the first three tools.
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.default` may be used to configure mkosi's image
building process. For example, you may configure the
distribution to use (`fedora`, `ubuntu`, `debian`, `archlinux`) 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
`mkosi` without further parameters in your *source* tree is
enough to get the right image of your choice set up.
Additionally if a `mkosi.default.d` directory exists, each file in it
is loaded in the same manner adding/overriding the values specified in
* `mkosi.extra` may be a directory. If this exists 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.
* `mkosi.build` may 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 `systemd-nspawn`), with
`$SRCDIR` pointing to the *source* tree. `$DESTDIR` points to a
directory where the script should place any files generated
it would like to end up in the *final* image. Note that
`make`/`automake` based build systems generally honour `$DESTDIR`,
thus making it very natural to build *source* trees from the
build script. After the *development* image was built and the
build script ran inside of it, it is removed again. After
that the *final* image is built, without any *source* tree or
build script copied in. However, this time the contents of
`$DESTDIR` is added into the image.
* `mkosi.postinst` may be an executable script. If it exists it is
invoked as last 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 `$SRCDIR`/`$DESTDIR` setup.
* `mkosi.nspawn` may 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
* `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.passphrase` may 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.crt` and `mkosi.secure-boot.key` may contain an
X509 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.
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.
Create and run a raw *GPT* image with *ext4*, as `image.raw`:
# systemd-nspawn -b -i image.raw
Create and run a bootable btrfs *GPT* image, as `foobar.raw`:
# mkosi -t raw_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 tar ball `image.raw.xz` and add a checksum
file, and install *SSH* into it:
# mkosi -d fedora -t tar --checksum --compress --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
BuildPackages=make gcc libcurl-devel
# cat > mkosi.build <<EOF
make -j `nproc`
# chmod +x mkosi.build
# systemd-nspawn -bi image.raw
mkosi is packaged for various distributions: Debian, Ubuntu, Arch (in AUR), Fedora.
It is usually easiest to use the distribution package.
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 squashfs-tools gnupg python3 tar veritysetup xz
Note that the minimum required Python version is 3.5.
If SecureBoot signing is to be used, then the "sbsign" tool needs to
be installed as well, which is currently not available on Fedora, but
in a COPR repository:
dnf copr enable msekleta/sbsigntool
dnf install sbsigntool