Nix: connecting to the Sandbox

brianmcgee · October 15, 2025, 3:25pm

fzakaria · October 15, 2025, 5:22pm

Something which is also not well known:

You can do nix develop and then run through all the “phases” of the derivation and see what part fails.

Look like Nix-build-phases: run nix build phases interactively has a nice UX around it.

imincik · October 16, 2025, 8:15am

This script was renamed to nix-develop-interactive and it contains usage instructions inside.

Recently I have integrated it in to Nix Forge so it can be enabled by simple setting debug = true; in a package recipe.

tomberek · October 16, 2025, 3:15pm

Another approach that has been useful in various situations, use tmate! trivial-builders: init addTmateBreakpoint by MatthewCroughan · Pull Request #334924 · NixOS/nixpkgs · GitHub

drupol · October 17, 2025, 6:34am

All these years without even knowing such a thing existed… Thank you !

phanirithvij · October 17, 2025, 9:25am

github.com/tmate-io/tmate

Can't ssh into terminal. Internal error. Connection to lon1.tmate.io closed.

opened 07:24AM - 17 Jul 25 UTC

PhilipFaure

We are having issues trying to ssh into our raspberry pi devices at several site…s. Usually we can ssh in remotely using: `ssh user/session@lon1.tmate.io` but now we get the following: ``` Internal error Connection to lon1.tmate.io closed. ``` Also tried different locations, e.g.: @ lon1, @ nyc1, @ sgp1, and @ sfo2. None of which work, and all giving the same "internal eror" message. We can now only ssh locally when on site. For example by using: `ssh user@192.168.0.xxx` when we are at the site, which is not ideal as these sites are on remote islands. I was at one of the sites yesterday trying to figure out what is going on and was able to create random session names, which I can still log in using for example: `<random_string_of_characters>@lon1.tmate.io` While on site, I tried to stop and restart the tmate service but this didn't help either. I also tried to use our tmate API to create a new named tmate session, but it gave me a randomly named session every time, e.g.: `<random_string_of_characters>@lon1.tmate.io`. The `.tmate.conf` is still in the home directory here: `~/.tmate.conf` and contains the session name and API key. So tmate should be able to find the right API and session name, right? I noticed that tmate.io website is not working, could the servers be down? Not sure what to do..

tmate maintainer says: “I’m closing the servers permanently”

djacu · October 17, 2025, 12:46pm

Oh no
any good alternatives?

phanirithvij · October 17, 2025, 1:02pm

There are some alternatives being discussed in that github issue.

randomizedcoder · October 17, 2025, 11:19pm

Very cool blog! Thank you!

It would be amazing to get some of this info added into some the tutorials, and/or other docs. - Sorry, but I’m not sure the best ones to put it into.

I wish I’d known about this about a week ago!

      nativeBuildInputs = [
        # add the breakpoint hook
        pkgs.breakpointHook
      ];

freerig · October 24, 2025, 1:56am

Oh nice!
This kind of reminds me the builtins.break feature which allows to open an interactive repl anywhere during the evaluation (to debug), in case anyone interested.