Havenāt looked into the implementation, but this sounds like a good candidate for nixpkgs.
Wow this is great and it would be even better if it could be upstreamed to nixpkgs (also nix-darwin and home-manager)!
ehmry
March 13, 2025, 8:40am
4
Unix has a nearly forgotten feature for registering port assignments - /etc/services. It canāt detect conflicts but it does provide a system-wide registry that can be accessed via getservbyname and getservbyport. This is useful for monitoring tools because they can use your port assignments to label traffic flows.
I had a PR to update the services file but it went stale and I wasnāt sure it was worth the eval overhead by itself. If it could be bolted onto conflict detection then I think it would be worth it.
NixOS:master ā ehmry:etc-services
opened 09:10AM - 30 Aug 23 UTC
## Description of changes
The `/etc/services` file is full of cruft. We can oā¦ verride it.
## Things done
- Built on platform(s)
- [x] x86_64-linux
- [ ] aarch64-linux
- [ ] x86_64-darwin
- [ ] aarch64-darwin
- [ ] For non-Linux: Is `sandbox = true` set in `nix.conf`? (See [Nix manual](https://nixos.org/manual/nix/stable/command-ref/conf-file.html))
- [x] Tested, as applicable:
- [NixOS test(s)](https://nixos.org/manual/nixos/unstable/index.html#sec-nixos-tests) (look inside [nixos/tests](https://github.com/NixOS/nixpkgs/blob/master/nixos/tests))
- and/or [package tests](https://nixos.org/manual/nixpkgs/unstable/#sec-package-tests)
- or, for functions and "core" functionality, tests in [lib/tests](https://github.com/NixOS/nixpkgs/blob/master/lib/tests) or [pkgs/test](https://github.com/NixOS/nixpkgs/blob/master/pkgs/test)
- made sure NixOS tests are [linked](https://nixos.org/manual/nixpkgs/unstable/#ssec-nixos-tests-linking) to the relevant packages
- [ ] Tested compilation of all packages that depend on this change using `nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD"`. Note: all changes have to be committed, also see [nixpkgs-review usage](https://github.com/Mic92/nixpkgs-review#usage)
- [ ] Tested basic functionality of all binary files (usually in `./result/bin/`)
- [23.11 Release Notes](https://github.com/NixOS/nixpkgs/blob/master/nixos/doc/manual/release-notes/rl-2311.section.md) (or backporting [23.05 Release notes](https://github.com/NixOS/nixpkgs/blob/master/nixos/doc/manual/release-notes/rl-2305.section.md))
- [ ] (Package updates) Added a release notes entry if the change is major or breaking
- [ ] (Module updates) Added a release notes entry if the change is significant
- [ ] (Module addition) Added a release notes entry if adding a new NixOS module
- [ ] Fits [CONTRIBUTING.md](https://github.com/NixOS/nixpkgs/blob/master/CONTRIBUTING.md).
3 Likes
Interesting. Iām not sure how much eval overhead this would generate, since every NixOS service would have to set an additional option. I implemented it for my own homelab, but would also be interested in upstreaming.
Whoa, Iād never heard of that. TIL. Thanks sir.
i hadnāt seen that PR
recently this file came up in another threadā¦ maybe there is more interest than i had anticipated
i had a different take than you had on what we could do with that fileā¦ see How to add extra ports to /etc/services? - #10 by aanderse for the rough idea
maybe worth investigating?
1 Like
vcunat
March 14, 2025, 9:11am
8
/etc/services is about protocols, not about particular daemons/services. Thatās how I view it.
bew
March 16, 2025, 11:58pm
9
May be time to revive that port allocator RFC?
NixOS:master ā lucasew:nixos/port-alloc
opened 01:28PM - 10 Jun 23 UTC
[Rendered](https://github.com/lucasew/rfcs/blob/nixos/port-alloc/rfcs/0151-nixosā¦ -port-alloc.md)
And/or the more generic allocator RFC?
NixOS:master ā lucasew:general-purpose-allocator-module
opened 04:13PM - 11 Aug 23 UTC
# Summary
This RFC is a rescope of #151.
This RFC defines a function that ā¦ returns a customized NixOS-like module that other modules can use to ask for allocated values and the module will check for invalid or undefined values or conflicts and suggest a value that solves the issue.
[Rendered](https://github.com/lucasew/rfcs/blob/general-purpose-allocator-module/rfcs/0159-general-purpose-allocator-module.md)
This Nix PR also has good inputs
NixOS:master ā nixcloud:builtins.port
opened 05:43PM - 03 Apr 17 UTC
# RFC
Using `builtins.port "myIdentifierString" one can allocated a dynamic aā¦ mount of `ports` but still be able to retrieve an assignement given a `identifier`.
```
services.nixcloud.apache.a = {
enable = true;
proxyOptions = {
port = builtins.port "my_identifier";
path = "/";
domain = "nix.a";
};
};
```
In the example above `port` would be assigned to `50000` and each time this `port` is referenced using `builtins.port "my_identifier"` it would return the same number `50000`.
A different configuration might use `builtins.port "webserver1"` and it would return `50001` since `"my_identifier"` already uses `50000`.
This PR still lacks documentation and is meant as a RFC.
**Note:** I couldn't find a way to express the `builtins.port` property in `nixpkgs/lib` as `nix` does not allow state in functions.
[ ] check if this is true: `eval-config.nix` can generate configurations for several VMs but `builtins.port` is global in the sense that it ignores that distinctive property, acting as a global singleton.
2 Likes
