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systemd-vmspawn - Man Page

Spawn an OS in a virtual machine


systemd-vmspawn [Options...] [ARGS...]


systemd-vmspawn may be used to start a virtual machine from an OS image. In many ways it is similar to systemd-nspawn(1), but launches a full virtual machine instead of using namespaces.

File descriptors for /dev/kvm and /dev/vhost-vsock can be passed to systemd-vmspawn via systemd's native socket passing interface (see sd_listen_fds(3) for details about the precise protocol used and the order in which the file descriptors are passed), these file descriptors must be passed with the names "kvm" and "vhost-vsock" respectively.

Note: on Ubuntu/Debian derivatives systemd-vmspawn requires the user to be in the "kvm" group to use the VSOCK options.


The excess arguments are passed as extra kernel command line arguments using SMBIOS.

The following options are understood:

-q,  --quiet

Turns off any status output by the tool itself. When this switch is used, the only output from vmspawn will be the console output of the Virtual Machine OS itself.

Added in version 256.

Image Options

-D,  --directory=

Directory to use as file system root for the virtual machine.

One of either --directory= or --image= must be specified. If neither are specified --directory=. is assumed.

Note: If mounting a non-root owned directory you may require --private-users= to map into the user's subuid namespace. An example of how to use /etc/subuid for this is given later.

Added in version 256.

-i,  --image=

Root file system disk image (or device node) for the virtual machine.

Added in version 255.

Host Configuration


The number of CPUs to start the virtual machine with. Defaults to 1.

Added in version 255.


The amount of memory to start the virtual machine with. Defaults to 2G.

Added in version 255.


If --kvm= is not specified KVM support will be detected automatically. If true, KVM is always used, and if false, KVM is never used.

Added in version 255.


If --vsock= is not specified VSOCK networking support will be detected automatically. If true, VSOCK networking is always used, and if false, VSOCK networking is never used.

Added in version 255.


Sets the specific CID to use for the guest. Valid CIDs are in the range 3 to 4294967294 (0xFFFF_FFFE). CIDs outside of this range are reserved. By default vmspawn will attempt to derive a CID for the guest derived from the machine name, falling back to a random CID if this CID is taken.

Added in version 255.


If --tpm= is not specified vmspawn will detect the presence of swtpm(8) and use it if available. If yes is specified swtpm(8) is always used, and if no is set swtpm(8) is never used.

Note: the virtual TPM used may change in future.

Added in version 256.


Set the linux kernel image to use for direct kernel boot. If a directory type image is used and --linux= was omitted, vmspawn will search for boot loader entries according to the Boot Loader Specification[1] assuming XBOOTLDR to be located at /boot and ESP to be /efi respectively. If no kernel was installed into the image then the image will fail to boot.

Added in version 256.


Set the initrd to use for direct kernel boot. If the --linux= supplied is a Boot Loader Specification[1] Type #2 entry, then this argument is not required. If no initrd was installed into the image then the image will fail to boot.

--initrd= can be specified multiple times and vmspawn will merge them together.

Added in version 256.

-n,  --network-tap

Create a TAP device to network with the virtual machine.

Note: root privileges are required to use TAP networking. Additionally, systemd-networkd(8) must be running and correctly set up on the host to provision the host interface. The relevant ".network" file can be found at /usr/lib/systemd/network/80-vm-vt.network.

Added in version 255.


Use user mode networking.

Added in version 255.


Takes an absolute path, or a relative path beginning with ./. Specifies a JSON firmware definition file, which allows selecting the firmware to boot in the VM. If not specified a suitable firmware is automatically discovered. If the special string "list" is specified lists all discovered firmwares.

Added in version 256.


Controls whether qemu processes discard requests from the VM. This prevents long running VMs from using more disk space than required. This is enabled by default.

Added in version 256.


Configure whether to search for firmware which supports Secure Boot.

If the option is not specified the first firmware which is detected will be used. If the option is set to yes then the first firmware with Secure Boot support will be selected. If no is specified then the first firmware without Secure Boot will be selected.

Added in version 255.

System Identity Options

-M,  --machine=

Sets the machine name for this virtual machine. This name may be used to identify this virtual machine during its runtime (for example in tools like machinectl(1) and similar).

Added in version 255.


Set the specified UUID for the virtual machine. The init system will initialize /etc/machine-id from this if this file is not set yet. Note that this option takes effect only if /etc/machine-id in the virtual machine is unpopulated.

Added in version 256.

Property Options


Controls whether the virtual machine is registered with systemd-machined(8). Takes a boolean argument, which defaults to "yes" when running as root, and "no" when running as a regular user. This ensures that the virtual machine is accessible via machinectl(1).

Note: root privileges are required to use this option as registering with systemd-machined(8) requires privileged D-Bus method calls.

Added in version 256.

User Namespacing Options


Controls user namespacing under --directory=. If enabled, virtiofsd(1) is instructed to map user and group ids (UIDs and GIDs). This involves mapping the private UIDs/GIDs used in the virtual machine (starting with the virtual machine's root user 0 and up) to a range of UIDs/GIDs on the host that are not used for other purposes (usually in the range beyond the host's UID/GID 65536).

If one or two colon-separated numbers are specified, user namespacing is turned on. UID_SHIFT specifies the first host UID/GID to map, UID_RANGE is optional and specifies number of host UIDs/GIDs to assign to the virtual machine. If UID_RANGE is omitted, 65536 UIDs/GIDs are assigned.

When user namespaces are used, the GID range assigned to each virtual machine is always chosen identical to the UID range.

Added in version 256.

Mount Options

--bind=PATH, --bind-ro=PATH

Mount a directory from the host into the virtual machine. Takes one of: a path argument — in which case the specified path will be mounted from the host to the same path in the virtual machine, or a colon-separated pair of paths — in which case the first specified path is the source in the host, and the second path is the destination in the virtual machine. If the source path is not absolute, it is resolved relative to the current working directory. The --bind-ro= option creates read-only bind mounts. Backslash escapes are interpreted, so "\:" may be used to embed colons in either path. This option may be specified multiple times for creating multiple independent bind mount points.

Added in version 256.


Takes a disk image or block device on the host and supplies it to the virtual machine as another drive.

Added in version 256.

Integration Options


Forward the virtual machine's journal to the host. systemd-journal-remote(8) is currently used to receive the guest VM's forwarded journal entries. This option determines where this journal is saved on the host and has the same semantics as -o/--output described in systemd-journal-remote(8).

Added in version 256.


By default an SSH key is generated to allow systemd-vmspawn to open a D-Bus connection to the VM's systemd bus. Setting this to "no" will disable SSH key generation.

The generated keys are ephemeral. That is they are valid only for the current invocation of systemd-vmspawn, and are typically not persisted.

Added in version 256.


Configures the type of SSH key to generate, see ssh-keygen(1) for more information.

By default "ed25519" keys are generated, however "rsa" keys may also be useful if the VM has a particularly old version of sshd.

Added in version 256.

Input/Output Options


Configures how to set up the console of the VM. Takes one of "interactive", "read-only", "native", "gui". Defaults to "interactive". "interactive" provides an interactive terminal interface to the VM. "read-only" is similar, but is strictly read-only, i.e. does not accept any input from the user. "native" also provides a TTY-based interface, but uses qemu native implementation (which means the qemu monitor is available). "gui" shows the qemu graphical UI.

Added in version 256.


Change the terminal background color to the specified ANSI color as long as the VM runs. The color specified should be an ANSI X3.64 SGR background color, i.e. strings such as "40", "41", ..., "47", "48;2;...", "48;5;...". See ANSI Escape Code (Wikipedia)[2] for details. Assign an empty string to disable any coloring. This only has an effect in --console=interactive and --console=read-only modes.

Added in version 256.


--load-credential=ID:PATH, --set-credential=ID:VALUE

Pass a credential to the virtual machine. These two options correspond to the LoadCredential= and SetCredential= settings in unit files. See systemd.exec(5) for details about these concepts, as well as the syntax of the option's arguments.

In order to embed binary data into the credential data for --set-credential=, use C-style escaping (i.e. "\n" to embed a newline, or "\x00" to embed a NUL byte). Note that the invoking shell might already apply unescaping once, hence this might require double escaping!

Added in version 255.



Do not pipe output into a pager.

-h,  --help

Print a short help text and exit.


Print a short version string and exit.



The maximum log level of emitted messages (messages with a higher log level, i.e. less important ones, will be suppressed). Takes a comma-separated list of values. A value may be either one of (in order of decreasing importance) emerg, alert, crit, err, warning, notice, info, debug, or an integer in the range 0...7. See syslog(3) for more information. Each value may optionally be prefixed with one of console, syslog, kmsg or journal followed by a colon to set the maximum log level for that specific log target (e.g. SYSTEMD_LOG_LEVEL=debug,console:info specifies to log at debug level except when logging to the console which should be at info level). Note that the global maximum log level takes priority over any per target maximum log levels.


A boolean. If true, messages written to the tty will be colored according to priority.

This setting is only useful when messages are written directly to the terminal, because journalctl(1) and other tools that display logs will color messages based on the log level on their own.


A boolean. If true, console log messages will be prefixed with a timestamp.

This setting is only useful when messages are written directly to the terminal or a file, because journalctl(1) and other tools that display logs will attach timestamps based on the entry metadata on their own.


A boolean. If true, messages will be prefixed with a filename and line number in the source code where the message originates.

Note that the log location is often attached as metadata to journal entries anyway. Including it directly in the message text can nevertheless be convenient when debugging programs.


A boolean. If true, messages will be prefixed with the current numerical thread ID (TID).

Note that the this information is attached as metadata to journal entries anyway. Including it directly in the message text can nevertheless be convenient when debugging programs.


The destination for log messages. One of console (log to the attached tty), console-prefixed (log to the attached tty but with prefixes encoding the log level and "facility", see syslog(3), kmsg (log to the kernel circular log buffer), journal (log to the journal), journal-or-kmsg (log to the journal if available, and to kmsg otherwise), auto (determine the appropriate log target automatically, the default), null (disable log output).


Whether to ratelimit kmsg or not. Takes a boolean. Defaults to "true". If disabled, systemd will not ratelimit messages written to kmsg.


Pager to use when --no-pager is not given; overrides $PAGER. If neither $SYSTEMD_PAGER nor $PAGER are set, a set of well-known pager implementations are tried in turn, including less(1) and more(1), until one is found. If no pager implementation is discovered no pager is invoked. Setting this environment variable to an empty string or the value "cat" is equivalent to passing --no-pager.

Note: if $SYSTEMD_PAGERSECURE is not set, $SYSTEMD_PAGER (as well as $PAGER) will be silently ignored.


Override the options passed to less (by default "FRSXMK").

Users might want to change two options in particular:


This option instructs the pager to exit immediately when Ctrl+C is pressed. To allow less to handle Ctrl+C itself to switch back to the pager command prompt, unset this option.

If the value of $SYSTEMD_LESS does not include "K", and the pager that is invoked is less, Ctrl+C will be ignored by the executable, and needs to be handled by the pager.


This option instructs the pager to not send termcap initialization and deinitialization strings to the terminal. It is set by default to allow command output to remain visible in the terminal even after the pager exits. Nevertheless, this prevents some pager functionality from working, in particular paged output cannot be scrolled with the mouse.

Note that setting the regular $LESS environment variable has no effect for less invocations by systemd tools.

See less(1) for more discussion.


Override the charset passed to less (by default "utf-8", if the invoking terminal is determined to be UTF-8 compatible).

Note that setting the regular $LESSCHARSET environment variable has no effect for less invocations by systemd tools.


Takes a boolean argument. When true, the "secure" mode of the pager is enabled; if false, disabled. If $SYSTEMD_PAGERSECURE is not set at all, secure mode is enabled if the effective UID is not the same as the owner of the login session, see geteuid(2) and sd_pid_get_owner_uid(3). In secure mode, LESSSECURE=1 will be set when invoking the pager, and the pager shall disable commands that open or create new files or start new subprocesses. When $SYSTEMD_PAGERSECURE is not set at all, pagers which are not known to implement secure mode will not be used. (Currently only less(1) implements secure mode.)

Note: when commands are invoked with elevated privileges, for example under sudo(8) or pkexec(1), care must be taken to ensure that unintended interactive features are not enabled. "Secure" mode for the pager may be enabled automatically as describe above. Setting SYSTEMD_PAGERSECURE=0 or not removing it from the inherited environment allows the user to invoke arbitrary commands. Note that if the $SYSTEMD_PAGER or $PAGER variables are to be honoured, $SYSTEMD_PAGERSECURE must be set too. It might be reasonable to completely disable the pager using --no-pager instead.


Takes a boolean argument. When true, systemd and related utilities will use colors in their output, otherwise the output will be monochrome. Additionally, the variable can take one of the following special values: "16", "256" to restrict the use of colors to the base 16 or 256 ANSI colors, respectively. This can be specified to override the automatic decision based on $TERM and what the console is connected to.


The value must be a boolean. Controls whether clickable links should be generated in the output for terminal emulators supporting this. This can be specified to override the decision that systemd makes based on $TERM and other conditions.


Example 1. Run an Arch Linux VM image generated by mkosi

$ mkosi -d arch -p systemd -p linux --autologin -o image.raw -f build
$ systemd-vmspawn --image=image.raw

Example 2. Import and run a Fedora 39 Cloud image using machinectl

$ curl -L \
       -O https://download.fedoraproject.org/pub/fedora/linux/releases/40/Cloud/x86_64/images/Fedora-Cloud-Base-40-1.10.x86_64.raw.xz \
       -O https://download.fedoraproject.org/pub/fedora/linux/releases/40/Cloud/x86_64/images/Fedora-Cloud-40-1.10-x86_64-CHECKSUM \
       -O https://fedoraproject.org/fedora.gpg
$ gpgv --keyring ./fedora.gpg Fedora-Cloud-40-1.10-x86_64-CHECKSUM
$ sha256sum -c Fedora-Cloud-40-1.10-x86_64-CHECKSUM
# machinectl import-raw Fedora-Cloud-Base-40-1.10.x86_64.raw.xz fedora-40-cloud
# systemd-vmspawn -M fedora-40-cloud

Example 3. Build and run systemd's system image and forward the VM's journal to a local file

$ mkosi build
$ systemd-vmspawn \
    -D mkosi.output/system \
    --private-users $(grep $(whoami) /etc/subuid | cut -d: -f2) \
    --linux mkosi.output/system.efi \
    --forward-journal=vm.journal \

Note: this example also uses a kernel command line argument to ensure SELinux isn't started in enforcing mode.

Example 4. SSH into a running VM using systemd-ssh-proxy

$ mkosi build
$ my_vsock_cid=3735928559
$ systemd-vmspawn \
    -D mkosi.output/system \
    --private-users $(grep $(whoami) /etc/subuid | cut -d: -f2) \
    --linux mkosi.output/system.efi \
    --vsock-cid $my_vsock_cid \
$ ssh root@vsock/$my_vsock_cid -i /run/user/$UID/systemd/vmspawn/machine-*-system-ed25519

Exit Status

If an error occurred the value errno is propagated to the return code. If EXIT_STATUS is supplied by the running image that is returned. Otherwise EXIT_SUCCESS is returned.

See Also

systemd(1), mkosi(1), machinectl(1), importctl(1), Boot Loader Specification[1]


  1. Boot Loader Specification
  2. ANSI Escape Code (Wikipedia)

Referenced By

importctl(1), machinectl(1), systemd.directives(7), systemd.index(7).

systemd 256.2