···

       
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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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+
       


     

       
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```bash

     

       
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-
       
❯ nix-shell -p iana-etc

     

       
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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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Nixpkg's version of [glibc](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/glibc/default.nix) 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_.