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Diffstat (limited to 'doc/builders/packages/etc-files.section.md')
| -rw-r--r-- | doc/builders/packages/etc-files.section.md | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/doc/builders/packages/etc-files.section.md b/doc/builders/packages/etc-files.section.md new file mode 100644 index 00000000000..2405a54634d --- /dev/null +++ b/doc/builders/packages/etc-files.section.md @@ -0,0 +1,18 @@ +# /etc files {#etc} + +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. + +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. + +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_. + + +```bash +> nix-shell -p iana-etc + +[nix-shell:~]$ env | grep NIX_ETC +NIX_ETC_SERVICES=/nix/store/aj866hr8fad8flnggwdhrldm0g799ccz-iana-etc-20210225/etc/services +NIX_ETC_PROTOCOLS=/nix/store/aj866hr8fad8flnggwdhrldm0g799ccz-iana-etc-20210225/etc/protocols +``` + +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_. |