systemd systemd-mountfsd.service 8 systemd-mountfsd.service systemd-mountfsd Disk Image File System Mount Service systemd-mountfsd.service /usr/lib/systemd/systemd-mountfsd systemd-mountfsd is a system service that dissects disk images, and returns mount file descriptors for the file systems contained therein to clients, via a Varlink IPC API. The disk images provided must contain a raw file system image or must follow the Discoverable Partitions Specification. Before mounting any file systems authenticity of the disk image is established in one or a combination of the following ways: If the disk image is located in a regular file in one of the directories /var/lib/machines/, /var/lib/portables/, /var/lib/extensions/, /var/lib/confexts/ or their counterparts in the /etc/, /run/, /usr/lib/ it is assumed to be trusted. If the disk image contains a Verity enabled disk image, along with a signature partition with a key in the kernel keyring or in /etc/verity.d/ (and related directories) the disk image is considered trusted. This service provides one Varlink service: io.systemd.MountFileSystem which accepts a file descriptor to a regular file or block device, and returns a number of file descriptors referring to an fsmount() file descriptor the client may then attach to a path of their choice. The returned mounts are automatically allowlisted in the per-user-namespace allowlist maintained by systemd-nsresourced.service8. The file systems are automatically fsck'ed before mounting. systemd1, systemd-nsresourced.service8