树莓派 ubuntu mate 16.04 系统默认软件源

deb http://ports.ubuntu.com/ xenial main restricted universe multiverse
deb-src http://ports.ubuntu.com/ xenial main restricted universe multiverse

deb http://ports.ubuntu.com/ xenial-updates main restricted universe multiverse
deb-src http://ports.ubuntu.com/ xenial-updates main restricted universe multiverse

deb http://ports.ubuntu.com/ xenial-security main restricted universe multiverse
deb-src http://ports.ubuntu.com/ xenial-security main restricted universe multiverse

deb http://ports.ubuntu.com/ xenial-backports main restricted universe multiverse
deb-src http://ports.ubuntu.com/ xenial-backports main restricted universe multiverse