Disk Usage (directory)

$ du
$ du -m
$ du -k
$ du -h
$ du -sh */
$ du -sh 
$ du -shc */
$ du -sbc */

Disk Free 

$ df       # default all filesystems
$ df .
$ df -h    # human-readable units

FileSystem ChecK (fsck)
perform this on unmounted or ro filesystem
$ sudo fsck /dev/sda5
$ sudo fsck -f /dev/sda5
$ sudo fsck -C /dev/sda5

Ext2 filesystem debugger
$ sudo debugfs /dev/sda5

Ext2 filesystem information
$ sudo dumpe2fs /dev/sda5

Tuning an ext2 filesystem

$ sudo tune2fs /dev/sda5

$ sudo mount
$ sudo mount /dev/sda5 /mnt
$ sudo umount /dev/sda5
$ sudo mount /dev/sda5 /mnt
$ sudo umount /mnt

# edit fstab to add /dev/sda5 with a mount point
# /dev/sda5	/home/xenos/NewMountPoint	ext3 defaults 0	0

$ sudo mount /dev/sda5 # now works because it's defined in /etc/fstab
$ sudo umount /home/xenos/NewMountPoint
$ sudo mount /home/xenos/NewMountPoint # same as above (etc fstab defined)
$ sudo umount /dev/sda5