Is there any way to copy a nix closure to a remote machine and protect it from being garbage collected remotely at the same time?
Nix currently has the
nix copy (e.g.
nix copy --to ssh://hostname /nix/store/n7kp7ascs2ifn4qwmqz3pcwrq893v9qg-bla.drv) command.
The manual page doesn’t say anything about gc root registration though.
Does anyone know how to make sure that the closure doesn’t get garbage collected?
One way: you can run
nix build /nix/store/path-to-keep --out-link /path/for/GC/symlink (on the target machine) – that symlink will keep the path alive while it exists (can be put anywhere). I find these useful in work directories.
The question here is that there currently might be no (nice) way of doing the registration atomically with copying.
I can confirm the
nix build can create the link in the
- given that now the user has to come up with his own name for the link, what are best practices in terms of location (e.g. should I put them in
/nix/var/nix/gcroots/auto?) and naming (e.g. should I also use hashes like the automatically created links?)?
- should I create an issue on github? cause I would assume
nix copyis supposed to be creating those links as otherwise you cannot even be sure that after the command successfully returns the path has not already been collected.
- I keep them in working directories that use those store paths, so that e.g. they get managed/deleted together, but other people might have completely different workflows. EDIT: usually they are just the automatic
nix buildinvocations done in those workdirs.
- I suppose it might be interesting for
nix copyto support
-o/--outlink, but I’ve given it almost no thought, so there might be much better approaches.
Note: I’m not really familiar yet with how gcroots are searched.
Hydra seems to
touch /nix/var/nix/gcroots/hydra/$(basename $path) to root a path.
This could be done before the copy, so it would be rooted before it even existed, and should be safe from GC.
Just an idea though, I haven’t tested this at all.
Yes, that should work, I think (or something similar). IIRC the disadvantage would be that you’d need to manually remove the link once you don’t want to keep it alive anymore. That’s different from
gcroots/auto used e.g. by
To do this atomically, I’ve always registered the upstream host as a substituter and run
nix-store -r /nix/store/arstd....hneio-hello --indirect --add-root ./result.