18 lines
1.3 KiB
Markdown
18 lines
1.3 KiB
Markdown
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# /etc files {#etc}
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Certain calls in glibc require access to runtime files found in /etc such as `/etc/protocols` or `/etc/services` -- [getprotobyname](https://linux.die.net/man/3/getprotobyname) is one such function.
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On non-NixOS distributions these files are typically provided by packages (i.e. [netbase](https://packages.debian.org/sid/netbase)) if not already pre-installed in your distribution. This can cause non-reproducibility for code if they rely on these files being present.
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If [iana-etc](https://hydra.nixos.org/job/nixos/trunk-combined/nixpkgs.iana-etc.x86_64-linux) is part of your _buildInputs_ then it will set the environment varaibles `NIX_ETC_PROTOCOLS` and `NIX_ETC_SERVICES` to the corresponding files in the package through a _setup-hook_.
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```bash
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❯ nix-shell -p iana-etc
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[nix-shell:~]$ env | grep NIX_ETC
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NIX_ETC_SERVICES=/nix/store/aj866hr8fad8flnggwdhrldm0g799ccz-iana-etc-20210225/etc/services
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NIX_ETC_PROTOCOLS=/nix/store/aj866hr8fad8flnggwdhrldm0g799ccz-iana-etc-20210225/etc/protocols
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```
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Nixpkg's version of [glibc](https://hydra.nixos.org/job/nixos/trunk-combined/nixpkgs.glibc.x86_64-linux) has been patched to check for the existence of these environment variables. If the environment variable are *not set*, then it will attempt to find the files at the default location within _/etc_.
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