HFS(plus) file system consistency check and repair.
The fsck_hfs utility verifies and repairs standard HFS and HFS+ file systems. It is not a GUI application but either an underlying background task or commandline utility.
The first form of fsck_hfs quickly checks the specified file systems to determine whether they were cleanly unmounted.
The second form of fsck_hfs preens the specified file systems. It is normally started by the parent fsck run from /etc/rc.boot during automatic reboot, when a HFS file system is detected. When preening file systems, fsck_hfs will fix common inconsistencies for file systems that were not unmounted cleanly. If more serious problems are found, fsck_hfs does not try to fix them, but indicates that it was not successful, and exits.
The third form of fsck_hfs checks the specified file systems and tries to repair all detected inconsistencies.
If no options are specified fsck_hfs will always check and attempt to fix the specified file systems.