3. Fixing corrupted ﬁle systems A ﬁle system can become corrupted in several ways. The most common of these ways are improper shutdown procedures and hardware failures. File systems may become corrupted during an unclean halt. This happens when proper shutdown procedures are not observed, physically write-protecting amounted ﬁle system, or amounted ﬁle system is taken offline. The most common operator procedural failure is forgetting to sync the system before halting the CPU. File systems may become further corrupted if proper startup procedures are not observed, e.g., not checking ale system for inconsistencies, and not repairing inconsistencies. Allowing a corrupted ﬁle system to be used (and, thus, to be modiﬁed further) can be disastrous. Any piece of hardware can fail at anytime. Failures can be as subtle as a bad block on a disk pack, or as blatant as a nonfunctional disk-controller.