The device specifier can either be a filename (i.e., /dev/sda1), or a LABEL or UUID specifier: "LABEL=volume-label" or "UUID=uuid". (i.e., LABEL=home or UUID=e40486c6-84d5-4f2f-b99c-032281799c9d).
Staggering the mount-counts at which file systems are forcibly checked will avoid all file systems being checked at one time when using journaled file systems.
Mount-count-dependent checking is disabled by default to avoid unanticipated long reboots while e2fsck does its work. If you are concerned about file system corruptions caused by potential hardware problems of kernel bugs, a better solution than mount-count-dependent checking is to use the e2scrub(8) program. This does require placing the file system on an LVM volume, however.
The only flag that can be set right now is strict which means that invalid strings should be rejected by the file system. In the default configuration, the strict flag is disabled.
WARNING: Removing an external journal from a file system which was not cleanly unmounted without first replaying the external journal can result in severe data loss and file system corruption.
There are pros and cons to disabling these periodic checks; see the discussion under the -c (mount-count-dependent check) option for details.
WARNING: The undo file cannot be used to recover from a power or system crash.