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https://github.com/flyingcircusio/userscan
Scans files for Nix store references and registers them with the Nix garbage collector.
https://github.com/flyingcircusio/userscan
Last synced: 5 days ago
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Scans files for Nix store references and registers them with the Nix garbage collector.
- Host: GitHub
- URL: https://github.com/flyingcircusio/userscan
- Owner: flyingcircusio
- License: bsd-3-clause
- Created: 2017-07-13T09:33:43.000Z (over 7 years ago)
- Default Branch: master
- Last Pushed: 2020-12-16T13:42:08.000Z (almost 4 years ago)
- Last Synced: 2024-08-02T12:49:35.366Z (3 months ago)
- Language: Rust
- Homepage:
- Size: 229 KB
- Stars: 35
- Watchers: 7
- Forks: 2
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
- Changelog: ChangeLog
- License: LICENSE
Awesome Lists containing this project
- awesome-starred - flyingcircusio/userscan - Scans files for Nix store references and registers them with the Nix garbage collector. (others)
README
# fc-userscan
Scans directories containing manually compiled programs and registers them with
the Nix garbage collector.
## Problem description
One can install fancy libs using `nix-env` and compile programs against them.
But, after a system update, the Nix garbage collector comes and pulls dynamic
link and other runtime dependencies out from under our manually compiled files.
This problem exists for some extent on all distros, but in NixOS it's amplified
by the fact that even smallest changes somewhere down the dependency chain will
change checksums from which Nix store paths are constructed.
## Solution
This tool allows to scan arbitrary directories and to register all Nix
dependencies found as GC roots so that they won't be taken away by the garbage
collector. Since plain string search is used, it works for both dynamic linkage
and other references, like config file paths.
## Example
Consider a Python virtualenv:
```ShellSession
$ nix-env --install python3
$ pyvenv myvenv
```
Now let's see if there are Nix store references present (hint: there are):
```ShellSession
$ fc-userscan -l myvenv
myvenv/bin/python3.5
/nix/store/a5zbx856hyfgz2isz0j60i8w44i6av09-python3-3.5.2
myvenv/pyvenv.cfg
/nix/store/a5zbx856hyfgz2isz0j60i8w44i6av09-python3-3.5.2
```
`fc-userscan` scans and registers Nix store references found either as symlinks
(like python3.5) or in files (pyvenv.cfg). The `-l` flag causes found references
to be dumped to stdout. At the same time, found references are registered with
the Nix garbage collector:
```ShellSession
$ ls -lR /nix/var/nix/gcroots/profiles/per-user/ckauhaus/home/ckauhaus/myvenv
/nix/var/nix/gcroots/profiles/per-user/ckauhaus/home/ckauhaus/myvenv
lrwxrwxrwx 1 ckauhaus users 57 Aug 11 13:29 a5zbx856hyfgz2isz0j60i8w44i6av09 -> /nix/store/a5zbx856hyfgz2isz0j60i8w44i6av09-python3-3.5.2
drwxr-xr-x 2 ckauhaus users 46 Aug 11 13:29 bin
/nix/var/nix/gcroots/profiles/per-user/ckauhaus/home/ckauhaus/myvenv/bin
lrwxrwxrwx 1 ckauhaus users 57 Aug 11 13:29 a5zbx856hyfgz2isz0j60i8w44i6av09 -> /nix/store/a5zbx856hyfgz2isz0j60i8w44i6av09-python3-3.5.2
```
All GC root registrations for a given dir $DIR go into
`/nix/var/nix/gcroots/profiles/per-user/$USER/$DIR` so this can easily be
inspected by the administrator. Should a reference vanish at the original
location, the registration will be cleaned up by the next run.
## Hacking
`fc-userscan` compiles with Rust 1.39.0 or higher.
To conveniently build setuid executables, install `cargo-make` and run `cargo
make suid`.
I'll happily accept pull requests at the [GitHub
repository](https://github.com/flyingcircusio/userscan).
Please write tests if feasible.
## Contact
The primary author of `fc-userscan` is [Christian
Kauhaus](mailto:[email protected]) or @ckauhaus on various online services.
## License
The software is licensed under a 3-clause BSD license.