How to reduce / file system utilization in Linux Server?

Reducing / file system utilization in linux server is very rare part.
or we can say, / file system is full, how to do housekeeping?

Situation:

We have separate mount of /boot /usr /tmp /home /var /opt file system but still / file system utilization is almost full.

Solution:

First check under / directory which are the file systems are not mounted, collect it & run the below command

For Ex: Below listed are not mounted, so we need to check which one is huge size.

admin lib middleware net  lib64 srv misc  media mnt

[root@testserver]# du -sk /admin /lib /middleware /net  /lib64 /srv /misc  /media /mnt | sort -n

4       /srv
16      /mnt
20      /middleware
31852   /lib64
920388  /lib

So lets see what's under /lib

[root@testserver ]# du -sk /lib/* | sort -n
109096  /lib/firmware
793332  /lib/modules

looks modules is huge size, lets check that one also

du -sk /lib/modules/* | sort -n

105840  /lib/modules/2.6.32-431.20.3.el6.x86_64
107040  /lib/modules/2.6.39-400.215.3.el6***.x86_64
109152  /lib/modules/2.6.32-504.23.4.el6.x86_64
116676  /lib/modules/2.6.32-696.1.1.el6.x86_64
176888  /lib/modules/3.8.13-68.3.3.el6***.x86_64
177732  /lib/modules/3.8.13-118.17.5.el6***.x86_64

Now Check the current kernal, which running on the server

[root@testserver firmware]# uname -a
Linux testserver 3.8.13-118.17.5.el6***.x86_64 #2 SMP Wed Apr 12 09:16:08 PDT 2017 x86_64 x86_64 x86_64 GNU/Linux

Check, what are the packages are related to 2.6 (old) kernel

#rpm -qf /lib/modules/2.6.*

kernel-2.6.32-431.20.3.el6.x86_64
kernel-2.6.32-504.23.4.el6.x86_64
kernel-2.6.32-696.1.1.el6.x86_64
kernel-uek-2.6.39-400.215.3.el6***.x86_64

We can see some old kernel is still available. So remove that one

#yum remove kernel-2.6.32-431.20.3.el6.x86_64

We can get some space if not sufficient then remove other (unused) older kernal.

Hope it helps.