nixos: make symlinks in /etc relative (except /etc/static)
#54980
Conversation
so that the links can be followed if the NixOS installation is not mounted as filesystem root. In particular, this makes /etc/os-release adhere to the standard: https://www.freedesktop.org/software/systemd/man/os-release.html Fixes NixOS#28833.
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Looks good to me. Not immediately useful to me as 1) I want read-only /etc with symlinks to mutable stuff and atomic switching — and I have it — and this change is only useful as long as you have |
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Pretty sure it's this PR, but after upgrading this morning, I've been getting boot warnings on One such example: |
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@eadwu I'll take a look |
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Same warnings here. Basically the check for
Some of this can be fixed but I don't know if there's a great answer for this that doesn't involve manually walking the filesystem or making some assumptions (perhaps enabled by constructing /etc to make this easier?). Well nevermind, I was puttering late at night so maybe there's a good answer here :). But I think this should be fixed soon and carefully. And if this is going to 19.03 resolving these warnings should be a blocker so as to not confuse or mislead users. It looks like |
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@dtzWill you were correct. I've spent a few hours trying to make this coversion isn't same as and none of it's primitives resolve I tend to reverting this PR, until I can figure out what is the most appropriate way to fix this. :( |
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On Fri, 22 Feb 2019 23:41:14 -0800, Danylo Hlynskyi ***@***.***> wrote:
@dtzWill you were correct.
:( I was hoping I'd missed something.
I've spent a few hours trying to make this coversion `/etc/udev/rules.d` -> `../static/udev/rules.d` -> `/etc/static/udev/rules.d`, but failed. Perl explicitly warns that
```
/etc/udev/../static/udev/rules.d
```
isn't same as
```
/etc/static/udev/rules.d
```
and none of it's primitives resolve `..` without taking symlink realpath. And realpath doesn't work, because `/etc/static` is itself tree of symlinks, so `/etc/static` realpath and `/etc/static/udev/rules.d` realpath are different.
I tend to reverting this PR, until I can figure out what is the most appropriate way to fix this. :(
I've reverted it locally for this reason.
If this can't be sorted out perhaps the original goal
re:`/etc/os-release` can just be special-cased?
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@danbst It turns out that checking if the symlink resolves to something inside /etc/static is indeed difficult. I think that you need to perform symlink resolution, just like the kernel does. The algorithm is not trivial to implement, but my rust (and python) versions are in http://github.com/layus/readlinks. Reimplementing this in perl will be error prone. My own implementation is still buggy. |
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@layus there is also This has to be solved in some other way. Currently "static" files are checked by being symlink to |
Motivation for this change
Main motivation is to fix extra-container, so it can run declarative NixOS containers on non-NixOS (erikarvstedt/extra-container#1 (comment)).
But seriously, there is a real problem with symlinking stuff currently. Let me show an example. Here's a simple container, where we override NixOS version.
Now let's see, if that works:
Indeed, in second case
/var/lib/containers/custom/etc/os-releasepoints to/etc/static/os-releaseof the host system, not container! This is wrong, but even worse happens on non-NixOS, where there is no/etc/staticon the host - container can be created and started, but can't be rebooted.This builds on top of #35364, however, I am not fixing the original problem (allow
machinectl pull-tarto run NixOS containers). I'll make a separate PR, which builds on top of this (and #35364) and makes/etcrelative symlink for container tarballs.cc @edolstra
cc @florianjacob as original author
cc @Ekleog @7c6f434c @erikarvstedt as potential interested parties
Things done
This makes symlinks relative in host's
/etctoo. Rebuild-switch is handled correctly, and my machine survives multiple reboots. Also,simpleinstaller NixOS test passes.sandboxinnix.confon non-NixOS)nix-shell -p nox --run "nox-review wip"./result/bin/)nix path-info -Sbefore and after)