I am unable to install php5-fpm from sudo apt-get install php5-fpm. It says:
No installation candidate.
No .deb repository link available. Does anyone have a solution?
php5-fpm is available in all supported Ubuntu releases, but is in universe in all of them. Try enabling universe, run sudo apt-get update and then try sudo apt-get install php5-fpm again.
You haven't stated the Ubuntu version you are using so this is just a wild guess. You are using the Ubuntu version which doesn't yet include php5-fpm package. This could be for various reasons – one most prominent might be the php5 version – php5-fpm was introduced from some point in time.
You have basically two options here:
Upgrade your Ubuntu to more recent version. You can find the availability of php5-fpm here: packages.ubuntu.com/php5-fpm
Upgrade your PHP version to most recent from my PPA, see the answer in another thread here: How do I install PHP 5.4.0?