Reclaim Hardisk space on /

Once in a while , whenever I checked my disk space usage ..

for / it goes up to 90% and left barely 1Gb out of 19Gb..

so whenever I did a yum install <bigthing>

it complain space insufficient..

it was allocated 19Gb for / .. and the rest goes to /home..

19Gb would be doubled of what being needed to do a full package install of CentOS.. as it only require upto 8-9 Gb..
was thinking to re-format this whole thing.. but wait.. may be it just time to do some clean up..
goes into runlevel 3 with

telinit 3

remove all temporary file

rm -rf /tmp/*
rm -rf /var/tmp/*

remove old kernel and kernel-devel

rpm -q kernel
yum remove kernel-<old-version-number>

and recheck the disk usage..

Hmm..

then it freed up to 7-8 Gb..

Seem back to normal.. don’t need to re-format.. Yay~