Hi all,
I want to dual boot bt5 and centos7. I have already installed bt5 with /boot=20GB and swap=4GB and gave the rest to / in a 320GB HDD. Is there any possibility with which I can dual boot? I read in this link that it is possible in a way. (http://www.linux.com/learn/answers/v...-linux-distros). Help is always appreciated.

regards,

At first, don't use Backtrack, it is outdated and not supported anymore. If you want to use a distro specialized for penetration testing go for Kali Linux, it is the successor of Backtrack.
Regarding dualboot, yes, you can dual boot any distro with CentOS. Just don't give all the remaining space on the disk to the / partition of the first OS, but leave enough free space for the second distro. I would partition in a way like this:
- /boot (1GB), not really needed
- / of first OS (20GB)
- / of second OS (20GB)
- swap, sized according to your RAM and workload, used by both OSes
The rest of the disk goes into a data partition that can be used by both OSes.
Also, I encourage to use LVM instead of traditional partitioning, this makes later repartitioning (maybe you want to delete one OS and give the space to the other, or you want to install a third OS, ...) very easy.

Thanks I will try it and reply. There is one more thing that KALI Linux never gets download completely always breaks in the middle. Also please provide some text or tutorial on how to use LVM.

regards,

Use the torrents instead of the normal download, this should eliminate that problem.
There is a whole bunch of tutorials for LVM out there, if you do a search for that, for example:
https://www.howtoforge.com/linux_lvm