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skipping heading levels (eg from # to ###, or starting at ###) is legal in pandoc, but not in nixos-render-docs. pandoc acts as though section levels *were* consecutive, nixos-render-docs prefers to tell people not to do that kind of thing because it can make documents more fragile.
16 lines
1.4 KiB
Markdown
16 lines
1.4 KiB
Markdown
# breakpointHook {#breakpointhook}
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This hook will make a build pause instead of stopping when a failure happens. It prevents nix from cleaning up the build environment immediately and allows the user to attach to a build environment using the `cntr` command. Upon build error it will print instructions on how to use `cntr`, which can be used to enter the environment for debugging. Installing cntr and running the command will provide shell access to the build sandbox of failed build. At `/var/lib/cntr` the sandboxed filesystem is mounted. All commands and files of the system are still accessible within the shell. To execute commands from the sandbox use the cntr exec subcommand. `cntr` is only supported on Linux-based platforms. To use it first add `cntr` to your `environment.systemPackages` on NixOS or alternatively to the root user on non-NixOS systems. Then in the package that is supposed to be inspected, add `breakpointHook` to `nativeBuildInputs`.
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```nix
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nativeBuildInputs = [ breakpointHook ];
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```
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When a build failure happens there will be an instruction printed that shows how to attach with `cntr` to the build sandbox.
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::: {.note}
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Caution with remote builds
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This won’t work with remote builds as the build environment is on a different machine and can’t be accessed by `cntr`. Remote builds can be turned off by setting `--option builders ''` for `nix-build` or `--builders ''` for `nix build`.
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:::
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