Feature Request: rollback command

[Shou]

It wasn't immediately obvious that you have to use the activate script in a generation's folder, but I feel like with a rollback command that takes a generation id that would be immediately obvious if one does a --help or man home-manager. Given that we already have a means to get from the id to the nix store generation path this should hopefully be trivial. The README also hints at a feature like this by saying it doesn't exist, but I don't see any issues for it (with my searching).

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[berbiche]

Still relevant

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Memorandum on closing issues

If you have nothing of substance to add, please refrain from commenting and allow the bot close the issue. Also, don't be afraid to manually close an issue, even if it holds valuable information.

Closed issues stay in the system for people to search, read, cross-reference, or even reopen--nothing is lost! Closing obsolete issues is an important way to help maintainers focus their time and effort.

[leira]

home-manager has been lacking a rollback feature for many years. I just want to understand what is the technical difficulty to have a rollback command?

[rycee]

I don't think there is any particular technical difficulty if one implement rollback by simply running an old activation script. This is the method suggested in the readme. The simple solution is not ideal, though, since it will create a new generation that effectively is a duplicate of the target generation. Ideally it would be possible to reuse the target generation by switching the "current generation link" to the target generation. To do this one would have to do various changes in the activation script. In any case, I think the reason why it hasn't been implemented is simply that nobody has had the time, knowledge, and motivation to do it. I don't really use rollbacks so it hasn't been a priority for me.

[leira]

@rycee Thanks for helping me understanding it!

[gilescope]

Feedback on how rollback is going:
just tried a rollback as the future used a newer glibc 2.34 that people are not all ready for on unstable.. but

/nix/store/yzcds1xs8zm52dsgiw4nh2h44k96qq0b-home-manager-generation/activate
Starting home manager activation
nix-build: /nix/store/q29bwjibv9gi9n86203s38n0577w09sx-glibc-2.33-117/lib/libc.so.6: version `GLIBC_2.34' not found (required by /nix/store/psijdi9190zgbp053y6dj3ax4y2l70gk-gcc-11.2.0-lib/lib/libstdc++.so.6)

Any suggestions? I was able to roll back the main OS but home-manager is stuck in the future. Would it be a really bad idea to run that activate script as sudo (where things are not messed up because nixos rolled back nicely)?

[gilescope]

(I managed to fix the underlying issue so I could roll forwards. Not being able to roll back is concerning, but I do understand that glibc is pretty essential.)

[hakan-demirli]

There is a dedicated section in home-manager manual about rollbacks.

Here is a command I frequently use to rollback home manager like grub menu nixos rollbacks.

bash $(home-manager generations | fzf | awk -F '-> ' '{print $2 "/activate"}')

This assumes you didn't nuke your bash, fzf, home-manager and awk programs. Most of the time only my desktop environment or terminal is nuked so I find it quite useful. I save it as a simple script in ~/.local/bin.

[rycee]

Will be resolved once #4976 (or similar) gets merged.