The Nix expressions for the X.org packages reside in pkgs/servers/x11/xorg/default.nix. This file is automatically generated from lists of tarballs in an X.org release. As such it should not be modified directly; rather, you should modify the lists, the generator script or the file pkgs/servers/x11/xorg/overrides.nix, in which you can override or add to the derivations produced by the generator. The generator is invoked as follows: $ cd pkgs/servers/x11/xorg $ cat tarballs-7.5.list extra.list old.list \ | perl ./generate-expr-from-tarballs.pl For each of the tarballs in the .list files, the script downloads it, unpacks it, and searches its configure.ac and *.pc.in files for dependencies. This information is used to generate default.nix. The generator caches downloaded tarballs between runs. Pay close attention to the NOT FOUND: name messages at the end of the run, since they may indicate missing dependencies. (Some might be optional dependencies, however.) A file like tarballs-7.5.list contains all tarballs in a X.org release. It can be generated like this: $ export i="mirror://xorg/X11R7.4/src/everything/" $ cat $(PRINT_PATH=1 nix-prefetch-url $i | tail -n 1) \ | perl -e 'while (<>) { if (/(href|HREF)="([^"]*.bz2)"/) { print "$ENV{'i'}$2\n"; }; }' \ | sort > tarballs-7.4.list extra.list contains libraries that aren’t part of X.org proper, but are closely related to it, such as libxcb. old.list contains some packages that were removed from X.org, but are still needed by some people or by other packages (such as imake). If the expression for a package requires derivation attributes that the generator cannot figure out automatically (say, patches or a postInstall hook), you should modify pkgs/servers/x11/xorg/overrides.nix.