When is it safe to use fsck?
Only use fsck on an unmounted or read-only filesystem. Running fsck on a r/w filesystem is dangerous and could corrupt the filesystem. If you bring the system up into single-user mode, the system will be mounted read-only. From there you can do an fsck -p to check all filesystems before bringing the system up into multi-user mode. If the filesystem has previously been marked “clean,” and you still want to check it, you can use the -f flag to fsck. If you do make any changes to the filesystem using fsck, it is probably best to type: reboot -n to reboot the machine immediately without syncing the disks.
