sevilay@sevilay-linux:~$ grep -ir toolchain /etc/apt/sources*

/etc/apt/sources.list.d/ubuntu-toolchain-r-ubuntu-test-xenial.list:deb http://ppa.launchpad.net/ubuntu-toolchain-r/test/ubuntu xenial main

/etc/apt/sources.list.d/ubuntu-toolchain-r-ubuntu-test-xenial.list:# deb-src http://ppa.launchpad.net/ubuntu-toolchain-r/test/ubuntu xenial main