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Inspect the file system.

Inspect the file system.

If a problem is suspected in the file system, use the fsck command to inspect the file system.
When the fsck command is executed, it will check the file system for abnormalities, and if any abnormalities are found, it will display a return value depending on the nature of the problem.
If no abnormality is found, the number of files contained on the disk, the number of blocks in use, and the number of available blocks will be displayed.
If the command is executed with no arguments, all devices described in /etc/fstab will be scanned, and if the command is executed with a device name specified as an argument, only the specified device will be scanned.

Since disk access while the check is in progress may destroy the system, it is safe to unmount any volume that can be unmounted when executing the fsck command, and to run it in single-user mode if it contains a volume on which / is placed.

[root@Lion ~]# fsck /dev/sda  ←Inspect the device “/dev/sda”.
fsck from util-linux 2.23.2
e2fsck 1.42.9 (28-Dec-2013)
/dev/sda is mounted.WARNING!!! Running e2fsck on a mounted filesystem may cause
SEVERE filesystem damage.Do you really want to continue (y/n)? yes ←Enter “y” if the target volume is unmounted or running in single user mode/boot: recovering journal
/boot: clean, 35/26104 files, 15397/104388 blocks  ←If there is no abnormality, the message “clean” will be displayed.

Return value when an abnormality is found by the fsck command
1:File system anomaly repaired.
2:We need to reboot the system.
4:ile system anomalies remain unrepaired.
8:operation error
16:Usage or grammatical errors
32:Canceled by user operation
128:Shared library error