Upgrade Debian Linux to Testing

See https://wiki.debian.org/DebianTesting.

Upgrade to testing

Basically (as root):

su -

apt-get update && apt-get upgrade -y
cat <<EOF >/etc/apt/sources.list
deb https://deb.debian.org/debian testing main contrib non-free
deb https://deb.debian.org/debian-security testing/updates main contrib non-free
EOF
apt-get update
apt-get dist-upgrade -y
apt autoremove -y

Then answer the questions.

If you enable extra architectures (see below), you might want to limit the architectures of the main repositories to amd64 (if you use that). So do this instead:

apt-get update && apt-get upgrade -y
cat <<EOF >/etc/apt/sources.list
deb [arch=amd64] https://deb.debian.org/debian testing main contrib non-free
deb [arch=amd64] https://deb.debian.org/debian-security testing/updates main contrib non-free
EOF
apt-get update
apt-get dist-upgrade -y
apt autoremove -y

Make apt prefer testing by default

If you are going to use multiple repos (e.g. debian-ports below), make testing the default like so:

echo 'APT::Default-Release "testing";' >/etc/apt/apt.conf.d/91prefertesting

Add support for new (hardware) ports

If you want to add support for new ports (e.g. RISC-V), do this:

apt-get install -y debian-ports-archive-keyring
cat <<EOF >>/etc/apt/sources.list
deb https://deb.debian.org/debian-ports unstable main
deb https://deb.debian.org/debian-ports unreleased main
deb https://deb.debian.org/debian-ports experimental main
EOF
apt-get update

Consider limiting the new ports to a specific architecture. Also consider limiting the main repositories to amd64 (if you use amd64). So do this instead:

apt-get install -y debian-ports-archive-keyring
cat <<EOF >>/etc/apt/sources.list
deb [arch=riscv64] https://deb.debian.org/debian-ports unstable main
deb [arch=riscv64] https://deb.debian.org/debian-ports unreleased main
deb [arch=riscv64] https://deb.debian.org/debian-ports experimental main
EOF
apt-get update