The root filesystem will be checked first unless the
-P 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_passnovalue of 0 are skipped and are not checked at all. Filesystems with a
fs_passnovalue of greater than zero will be checked in order, with filesystems with the lowest
fs_passnonumber being checked first. If there are multiple filesystems with the same pass number,
fsckwill attempt to check them in parallel, although it will avoid running multiple filesystem checks on the same physical disk.
Hence, a very common configuration in /etc/fstab files is to set the root filesystem to have a
fs_passnovalue of 1 and to set all other filesystems to have a
fs_passnovalue of 2. This will allow
fsckto 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.
I have one physical disk on my machine, with two filesystems one vfat this is the ESP and the other is ext4 this is mounted on root
/, each having fs_passno value of 1. The first paragraph in the manual page states that
fsck avoids "multiple filesystem checks on the same physical disk."
Confusingly the second paragraph implies that filesystems with
fs_passno of value 2 will be run in parallel and does not say that they might not run parallel on the same disk. In my case, what would be the case? Parallel or not parallel?