What is checked
- Field count, device spec form (UUID, LABEL, PARTUUID, paths, host:/export, //host/share), and kernel names such as /dev/sda1 that can change.
- Mount points: absolute paths,
none for swap, duplicates, and a child listed before its parent.
- Filesystem types and options: unknown options, contradictions (
ro with rw), options that belong to another filesystem (subvol= outside btrfs), network mounts without _netdev, passwords in options, tmpfs without a size.
- The dump and pass fields: only the root filesystem should use pass 1, and filesystems without fsck should use 0.
- Hardening hints for /tmp, /dev/shm, /var/tmp, /home, /boot and the EFI partition.
Limits
This is a static check. It cannot see your disks, so it cannot tell whether a UUID exists. Run blkid to confirm UUIDs and findmnt --verify (util-linux 2.29 or newer) before you reboot. An error in fstab can drop the machine to emergency mode at the next boot.
The Arch installer tool has a fstab builder if you want to create entries instead of checking them.