To install Unrar on CentOS, run

cd /usr/local/src
wget http://www.rarlab.com/rar/rarlinux-3.8.0.tar.gz
tar zxvf rarlinux-3.8.0.tar.gz
cd rar
make
make install

We installed older version of unrar as Latest unrar will not work on CentOS 5.x

To check where unrar installed, run which unrar

root@server20 [~]# which unrar
/usr/local/bin/unrar
root@server20 [~]#