What is "downgrading a system"?
Is it supported?
Short answer: No, it isn't supported.
- Long answer: It isn't supported because
- The packages' installation scripts (postinst...) are designed to handle upgrade only.
The installation tools are designed to replace older versions of packages by newer versions.
So, what's the supported way?
- Make a backup of your system before you upgrade, so you can restore your backup to "downgrade" it!
But I am desperate since I have no backup ...
There are some workarounds to save your system, provided you know where your important data is. They may be in your home directory, /etc/, /mail/, ....
- If an upgrade caused your system to break, boot your system with a live CD/USB-key etc., and make a backup of your private data somewhere (USB connected HDD, SSH connected remote system, ...).
- Make a fresh new system install.
- Restore your private data from the back up.
But I am desperate and lazy ...
Here is a totally unsupported trick which may work in some lucky situations. (Desktop focused example)
System downgrade tends to be more successful, if there aren't many packages installed. No GUI program and no TeX is good idea. I mean removing practically all non-essential packages is the trick I know the following is very terse. If this is too cryptic, try the above method with live CD/USB-key, instead.
- Save data and stop all your Desktop tasks.
- CTRL-ALT-F3 to get to console and login as root.
Start aptitude -u
Press l to open a dialog.
- Press 'M' on 'Installed Packages' line and press '['.
- Press 'm' on key packages like 'vim' 'mc' 'git' 'ssh' 'exim4-daemon-light' ... (packages you need to keep.)
- Press '+' on key packages to be installed.
- Press '+' again if key packages show 'B' to resolve broken dependency.
- Press 'g' (resolve broken dependency as needed) to remove all non-essential packages.
Edit /etc/apt/sources.list to point repository to the downgraded distribution.
Set apt_preferences(5) to set the downgraded distribution with PIN 10001
Run "apt update; apt full-upgrade" to downgrade system.
Run aptitude -u to interactively resolve issues.
Remove apt_preferences(5) PIN.
Run aptitude -u and install system. (Use task list in aptitude and information from backed up /var/lib/dpkg/status.)
- If you are lucky, you may have somewhat functioning system. No guarantee of stability!!!