Permission problem when installing package from tlmgr

What I did was to let sudo know about the modification of the $PATH variable. This was done typing the following command on terminal

sudo env PATH="$PATH" tlmgr

In this way, I somehow enabled sudo in tlmgr. After that packages can be installed using

sudo tlmgr install package

In case anyone else tried previous suggestions and they didn't work, this worked for me:

sudo /usr/local/texlive/2015/bin/x86_64-linux/tlmgr ...