find out notusable data in linux

How to keep disk-space to free from not usable data in LINUX/Unix:

Agedu: Correlate disk usage with last-access times to identify large and disused data
                 agedu scans a directory tree and produces reports about how much disk space is used in each directory and subdirectory, and also how that usage of disk space corresponds to files with last-access times a long time ago.
                 In other words, agedu is a tool you might use to help you free up disk space. It lets you see which directories are taking up the most space, as du does; but unlike du, it also distinguishes between large collections of data which are still in use and ones which have not been accessed in months or years - for instance, large archives downloaded,unpacked, used once, and never cleaned up. Where du helps you find what's using your disk space, agedu helps you find what's wasting your disk space.

How to install:
==> for Debian / Ubuntu Linux user type the following apt-get command to install agedu:
$sudo  apt-get install agedu

==> for RHEL / CentOS / Fedora users  turn on EPEL repo and type the following
#yum install agedu

Example how to use it:

Step1: The following command will conllect information about disk used by files in /home/shankar directory.

agedu -s /home/shankar/

Step2: Then execute the following command on command prompt to view the disk usage in web browser:

agedu -w

you will see the following output :

Using Linux /proc/net magic authentication

URL: http://127.0.0.1:42823/

Use this url in web browser and you will see the file and folder level usage graphically.

Note: Don't stop this command.

For more information use man agedu