Certain calls in glibc require access to runtime files found in
/etc such as
/etc/services -- getprotobyname is one such function.
On non-NixOS distributions these files are typically provided by packages (i.e., 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 is part of your
buildInputs, then it will set the environment variables
NIX_ETC_SERVICES to the corresponding files in the package through a setup hook.
> 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 has been patched to check for the existence of these environment variables. If the environment variables are not set, then it will attempt to find the files at the default location within