It's a good idea to run chkfsys as part of your regularly scheduled maintenance procedures; this lets you verify that the data on your disk is intact.
For example, you might consider running chkfsys on your network servers every time they boot. An automated check on the filesystem at boot time guarantees that chkfsys will attempt to fix any problems it finds during the scan.
It's especially important to run chkfsys after a system crash, power outage, or unexpected system reboot so that you can identify whether any files have been damaged. The chkfsys utility checks the "clean" flag on the disk to determine whether the system was in a consistent state at the time.
The clean flag is stored on disk and is maintained by the system. The flag is turned off when the filesystem is mounted and is turned on when the filesystem is unmounted. When the clean flag is set, chkfsys assumes that the filesystem is intact. If chkfsys finds the clean flag off, it tries to fix the problem.
The chkfsys utility supports a -u option, which overrides a set clean flag and tells chkfsys to run unconditionally. You might want to override the clean flag when: