Repair a Linux File system (ext2 ext3) and FSCK

1) File system must be unmounted, you cannot repair it while it is running. Take system down to runlevel one (make sure you run all command as root user):
# init 1

2)Unmount file system, for example if it is /home (/dev/sda3) file system then type command:
# umount /home
OR
# umount /dev/sda3

3) Now run fsck on the partition:
# fsck /dev/sda3

However be sure to specify the file system type using -t option. Otherwise, Result would be more corruption as fsck by default assumes ext2 file system.
# fsck -t ext3 /dev/sda3
OR
# fsck.ext3 /dev/sda3

Tip if you don’t know your file system type then typing mount command will display file system type.

fsck will check the file system and ask which problems should be fixed or corrected. If you don’t wanna type y every time then you can use pass -y option to fsck.
# fsck -y /dev/sda3

Please not if any files are recovered then they are placed in /home/lost+found directory by fsck command.

4) Once fsck finished, remount the file system:
# mount /home

5) Go to multiuser mode
# init 3

Read man page of fsck for more information. Make sure you replace /dev/sda3 with your actual device name.

FSCK on NEXT REBOOT

A. fsck is used to check and optionally repair one or more Linux file systems. You don’t have to create or alter/modify any file. All you need to do is just create empty file /forcefsck.
Force fsck on boot using /forcefsck

By creating /forcefsck file you will force the Linux system (or rc scripts) to perform a full file system check.