systemd-machine-id-setup - Man Page

Initialize the machine ID in /etc/machine-id

Examples (TL;DR)

Print the generated or committed machine ID: systemd-machine-id-setup --print
Specify an image policy: systemd-machine-id-setup --image-policy your_policy
Display the output as JSON: sudo systemd-machine-id-setup --json pretty
Operate on a disk image instead of a directory tree: systemd-machine-id-setup --image /path/to/image

systemd-machine-id-setup may be used by system installer tools to initialize the machine ID stored in /etc/machine-id at install time, with a provisioned or randomly generated ID. See machine-id(5) for more information about this file.

If the tool is invoked without the --commit switch, /etc/machine-id is initialized with a valid, new machine ID if it is missing or empty. The new machine ID will be acquired in the following fashion:

If a valid machine ID is stored in /run/machine-id, the machine ID is copied and used to initialize the machine ID in /etc/machine-id. This step is skipped if --root= is specified or running in a chroot environment.
If a valid D-Bus machine ID is already configured for the system, the D-Bus machine ID is copied and used to initialize the machine ID in /etc/machine-id.
If a valid machine ID is provided through system.machine_id credential, the machine ID is copied and used to initialize the machine ID in /etc/machine-id. This step is skipped if --root= is specified or running in a chroot environment.
If run inside a KVM virtual machine and a UUID is configured (via the -uuid option), this UUID is used to initialize the machine ID. The caller must ensure that the UUID passed is sufficiently unique and is different for every booted instance of the VM. This step is skipped if --root= is specified or running in a chroot environment.
Similarly, if run inside a Linux container environment and a UUID is configured for the container, this is used to initialize the machine ID. For details, see the documentation of the Container Interface^[1]. This step is skipped if --root= is specified or running in a chroot environment.
Otherwise, a new ID is randomly generated.

The --commit switch may be used to commit a transient machined ID to disk, making it persistent. For details, see below.

Use systemd-firstboot(1) to initialize the machine ID on mounted (but not booted) system images.

Options

The following options are understood:

--root=path

Takes a directory path as argument. All paths operated on will be prefixed with the given alternate root path, including the path for /etc/machine-id itself.

Added in version 212.

--image=path

Takes a path to a device node or regular file as argument. This is similar to --root= as described above, but operates on a disk image instead of a directory tree.

Added in version 249.

--image-policy=policy

Takes an image policy string as argument, as per systemd.image-policy(7). The policy is enforced when operating on the disk image specified via --image=, see above. If not specified, defaults to the "*" policy, i.e. all recognized file systems in the image are used.

--commit

Commit a transient machine ID to disk. This command may be used to convert a transient machine ID into a persistent one. A transient machine ID file is one that was bind mounted from a memory file system (usually "tmpfs") to /etc/machine-id during the early phase of the boot process. This may happen because /etc/ is initially read-only and was missing a valid machine ID file at that point.

This command will execute no operation if /etc/machine-id is not mounted from a memory file system, or if /etc/ is read-only. The command will write the current transient machine ID to disk and unmount the /etc/machine-id mount point in a race-free manner to ensure that this file is always valid and accessible for other processes.

This command is primarily used by the systemd-machine-id-commit.service(8) early boot service.

Added in version 227.

--print