Modern journaling file systems are designed such that tools such as fsck do not need to be run after unclean shutdown (. crash). The UFS2 Filesystem in FreeBSD has a background fsck, so it is usually not necessary to wait for fsck to finish before accessing the disk. Full copy-on-write file systems such as ZFS and Btrfs are designed to avoid most causes of corruption and have no traditional "fsck" repair tool. Both have a "scrub" utility which examines and repairs any problems; in the background and on a mounted filesystem.