Permission issue in cache and logs folder in Symfony 2.0

I have tried some ways to give permission to the cache & logs folder but whenever I clear cache at that time the problem occurs like unable to write in directory.

I have tried this two ways:

1. Full access to cache via the root user with 777 permissions.
2. Change the owner like www-data as said in Symfony2 docs.

but it didn't work for me.