* On systems that have the setresuid() and setresgid() system calls to

set the real uid and gid to the effective uid and gid, the Nix
  binaries can be installed as owned by the Nix user and group instead
  of root, so no root involvement of any kind is necessary.

  Linux and FreeBSD have these functions.

src/Makefile.am

@@ -4,5 +4,10 @@ SUBDIRS = bin2c boost libutil libstore libmain nix-store nix-hash \
 SETUID_PROGS = nix-store nix-instantiate nix-env
 install-exec-hook:
 if SETUID_HACK
+if HAVE_SETRESUID
+	cd $(DESTDIR)$(bindir) && chown @NIX_USER@ $(SETUID_PROGS) \
+	  && chgrp @NIX_GROUP@ $(SETUID_PROGS) && chmod ug+s $(SETUID_PROGS)
+else
 	cd $(DESTDIR)$(bindir) && chown root $(SETUID_PROGS) && chmod u+s $(SETUID_PROGS)
 endif
+endif