Linux will run fsck automatically at boot time if the filesystem has been unchecked for a long time or there is a reason (unsafe reboot after a power glitch) to suspect it's been corrupted. You can run fsck manually.

1. To check for errors on a partition or filesystem, pass the path to fsck:

        # fsck /dev/sdb3
        fsck from util-linux 2.20.1
        e2fsck 1.42.5 (29-Jul-2012)
        HDD2 has been mounted 26 times without being checked, check forced.
        Pass 1: Checking inodes, blocks, and sizes
        Pass 2: Checking directory structure
        Pass 3: Checking directory connectivity
        Pass 4: Checking reference counts
        Pass 5: Checking group summary information
        HDD2: 75540/16138240 files (0.7% non-contiguous),      
        48756390/64529088 blocks

2. The -A flag checks all the filesystems configured in /etc/fstab:

        # fsck -A

This will go through the /etc/fstab file, checking each filesystem. The fstab file defines the mapping between physical disk partitions and mount points. It's used to mount filesystems during boot.

3. The -a option instructs fsck to automatically attempt to fix errors, instead of interactively asking us whether or not to repair them. Use this option with caution:

        # fsck -a /dev/sda2

4. The -N option simulates the actions fsck will perform:

        # fsck -AN
        fsck from util-linux 2.20.1
        [/sbin/fsck.ext4 (1) -- /] fsck.ext4 /dev/sda8
        [/sbin/fsck.ext4 (1) -- /home] fsck.ext4 /dev/sda7
        [/sbin/fsck.ext3 (1) -- /media/Data] fsck.ext3 /dev/sda6