17 August 2016

As the title says, it’s possible to downgrade FreeBSD without reinstalling. You void the warranty and people start looking at you funny when you talk about this stuff, so do yourself a favor and use ZFS snapshotting.

If you can still access the network, whether it be from the install itself, or a bootable memstick image, this will work for you. Even across major releases, unless you’ve run a zpool upgrade. In our working example, assume we’re on 11.0 and want to go back to 10.3. The method is pretty similar to upgrading, with the exception that you don’t reboot until the very end. Here’s the incantation:

# freebsd-update -r 10.3-RELEASE upgrade
# freebsd-update install
# freebsd-update install
# pwd_mkdb /etc/master.passwd
# pkg-static install -fy pkg
# pkg upgrade -fy
# reboot

This can be executed over SSH for remote downgrading fun. Throw it in orchestration for O(fun).