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3rd chunk of `fsck.man`
8e90da1df32ca64350e5442ba5d2230958ab3b33813bf58f0000000100000dd9
 option is
           specified (see below). After that, filesystems will be checked in
           the order specified by the fs_passno (the sixth) field in the
           /etc/fstab file. Filesystems with a fs_passno value of 0 are skipped
           and are not checked at all. Filesystems with a fs_passno value of
           greater than zero will be checked in order, with filesystems with
           the lowest fs_passno number being checked first. If there are
           multiple filesystems with the same pass number, fsck will attempt to
           check them in parallel, although it will avoid running multiple
           filesystem checks on the same physical disk.

           fsck does not check stacked devices (RAIDs, dm-crypt, ...) in
           parallel with any other device. See below for
           FSCK_FORCE_ALL_PARALLEL setting. The /sys filesystem is used to
           determine dependencies between devices.

           Hence, a very common configuration in /etc/fstab files is to set the
           root filesystem to have a fs_passno value of 1 and to set all other
           filesystems to have a fs_passno value of 2. This will allow fsck to
           automatically run filesystem checkers in parallel if it is
           advantageous to do so. System administrators might choose not to use
           this configuration if they need to avoid multiple filesystem checks
           running in parallel for some reason - for example, if the machine in
           question is short on memory so that excessive paging is a concern.

           fsck normally does not check whether the device actually exists
           before calling a filesystem specific checker. Therefore non-existing
           devices may cause the system to enter filesystem repair mode during
           boot if the filesystem specific checker returns a fatal error. The
           /etc/fstab mount option nofail may be used to have fsck skip
           non-existing devices. fsck also skips non-existing devices that have
           the special filesystem type auto.

       -C [fd]
           Display completion/progress bars for those filesystem checkers
           (currently only for ext[234]) which support them. fsck will manage
           the filesystem checkers so that only one of them will display a
           progress bar at a time. GUI front-ends may specify a file descriptor
           fd, in which case the progress bar information will be sent to that
           file descriptor.

       -M
           Do not check mounted filesystems and return an exit status of 0 for
           mounted filesystems.

       -N
           Don’t execute, just show what would be done.

       -P
           When the -A flag is set, check the root filesystem in parallel with
           the other filesystems. This is not the safest thing in the world to
           do, since if the root filesystem is in doubt things like the
           e2fsck(8) executable might be corrupted! This option is mainly
           provided for those sysadmins who don’t want to repartition the root
           filesystem to be small and compact (which is really the right
           solution).

       -R
           When checking all filesystems with the -A flag, skip the root
           filesystem. (This is useful in case the root filesystem has already
           been mounted read-write.)

       -T
           Don’t show the title on startup.

       -V
           Produce verbose output, including all filesystem-specific commands
           that
Title: fsck Options: fstab Configuration, Progress Bars, and Root Filesystem Handling
Summary
This section describes fsck options, including the recommended /etc/fstab configuration with fs_passno values for parallel filesystem checking and cautions against excessive parallel checks on memory-constrained systems. It covers the '-C' option for displaying progress bars, '-M' for skipping mounted filesystems, '-N' for a dry run, '-P' for checking the root filesystem in parallel (with associated risks), '-R' for skipping the root filesystem, '-T' for suppressing the title, and '-V' for verbose output.