Sometimes we are clueless which directories are eating up all the disk space on our Linux Server. There are few ways to find them out.
Most of the directories that’s particularly growing up are /var, /tmp, or /home
1. Type the following command at the shell prompt to find out top 10 largest file/directories:

[root@server1 ~]# du -a /var | sort -n -r | head -n 10


du : Estimate file space usage.
sort : Sort lines of text files or given input data.
head : Output the first part of files i.e. to display first 10 largest file.

Output:

13075456 /var
9078732 /var/www
4351176 /var/log/
3769656 /var/lib
2677596 /var/log/btmp
2466664 /var/lib/awstats
1328512 /var/log/httpd
1213832 /var/lib/varnish
1049600 /var/lib/varnish/varnish_storage.bin
682296  /var/lib/awstats/awstats082012.txt

2. If you want more human readable output try:

[root@server1 ~]# cd /var
[root@server1 var]# du -hsx * | sort -r | head -10
# SAMPLE OUTPUT
96M     tmp
8.7G    log
8.4M    db
8.0K    racoon
8.0K    preserve
8.0K    opt
8.0K    nis
8.0K    net-snmp
8.0K    local
8.0K    games


Where,
du command -h option : display sizes in human readable format (e.g., 1K, 234M, 2G).
du command -s option : show only a total for each argument (summary).
du command -x option : skip directories on different file systems.
sort command -r option : reverse the result of comparisons.
head command -10 OR -n 10 option : show the first 10 lines.


3. Finding directories over 1GB

[root@server1 ~]# du -h / | grep ^[0-9.]*G
# SAMPLE OUTPUT
2.4G    /var/lib/awstats
1.2G    /var/lib/varnish
3.6G    /var/lib
1.3G    /var/log/httpd
4.2G    /var/log/varnish
8.8G    /var/log
13G     /var
1.4G    /usr
15G     /opt
122G    /data
2.8G    /root
2.2G    /home/user

4. To find directories over 10GB and sort the output with the largest directories on top

[root@server1 ~]#  du -h / | grep ^[1-9][0-9][0-9.]*G | sort -rn

5. To find directories over 200GB

[root@server1 ~]# du -h / | grep ^[2-9][0-9][0-9][0-9.]*G