Check the integrity of a filesystem or repair it. The filesystem should be unmounted at the time the command is run. It is a wrapper that calls 'fsck_hfs', 'fsck_apfs', 'fsck_msdos', 'fsck_exfat', and 'fsck_udf' as needed.

# To check filesystem /dev/sda, reporting any damaged blocks:
fsck </dev/sda>

# To check filesystem /dev/sda only if it is clean, reporting any damaged blocks and interactively letting the user choose to repair each one:
fsck -f </dev/sda>

# To check filesystem /dev/sda only if it is clean, reporting any damaged blocks and automatically repairing them:
fsck -fy </dev/sda>

# To check filesystem /dev/sda, reporting whether it has been cleanly unmounted:
fsck -q </dev/sda>