systemd-fsck@.service, systemd-fsck-root.service, systemd-fsck — File system checker logic
systemd-fsck@.service
systemd-fsck-root.service
/usr/lib/systemd/systemd-fsck
systemd-fsck@.service and
                systemd-fsck-root.service are
                services responsible for file system checks. They are
                instantiated for each device that is configured for
                file system checking.
                systemd-fsck-root.service is
                responsible for file system checks on the root file
                system, but in only if the root filesystem wasn't
                checked in the initramfs.
                systemd-fsck@.service is used for
                all other file systems and for the root file system in
                the initramfs.
Those services are started at boot if
                passno in
                /etc/fstab for the file system is
                set to a value greater than zero. The file system
                check for root is performed before the other file
                systems. Other file systems may be checked in
                parallel, except when they are one the same rotating
                disk.
systemd-fsck does not know
                any details about specific filesystems, and simply
                executes file system checkers specific to each
                filesystem type (/sbin/fsck.*).
                This helper will decide if the filesystem should
                actually be checked based on the time since last
                check, number of mounts, unclean unmount, etc.
systemd-fsck will forward
                file system checking progress to the console. If a
                file system check fails for a service without
                nofail, emergency mode is activated,
                by isolating to
                emergency.target.
systemd-fsck understands
                one kernel command line parameter:
fsck.mode=¶One of
                                "auto",
                                "force",
                                "skip". Controls the
                                mode of operation. The default is
                                "auto", and ensures
                                that file system checks are done when
                                the file system checker deems them
                                necessary. "force"
                                unconditionally results in full file
                                system checks. "skip"
                                skips any file system
                                checks.
fsck.repair=¶One of
                                "preen",
                                "yes",
                                "no". Controls the
                                mode of operation. The default is "
                                preen", and will automatically repair
                                problems that can be safely fixed. "yes
                                " will answer yes to all questions by
                                fsck and "no" will answer no to
                                all questions.