systemd-mountfsd.service, systemd-mountfsd - Disk Image File System Mount Service

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 DiscoverablePartitionsSpecification[1]. Before mounting any file systems authenticity of the disk image is established in one
       or a combination of the following ways:

        1. 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.

        2. 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[2] 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.service(8).

       The file systems are automatically fsck(8)'ed before mounting.

       systemd-mountfsd.service, systemd-mountfsd - Disk Image File System Mount Service

        1. Discoverable Partitions Specification
           https://uapi-group.org/specifications/specs/discoverable_partitions_specification/

        2. Varlink
           https://varlink.org/

systemd 257.7                                                                        SYSTEMD-MOUNTFSD.SERVICE(8)

systemd(1), systemd-nsresourced.service(8)

       systemd-mountfsd.service

       /usr/lib/systemd/systemd-mountfsd