Taken from: https://groups.google.com/g/linux.debian.bugs.dist/c/mX4GpUJih4k.

--- a/configure.ac
+++ b/configure.ac
@@ -132,6 +132,16 @@ if test "$os_unix" = "yes"; then
 	AC_CHECK_FUNCS([getpeereid])
 	AC_CHECK_FUNCS([getpeerucred])
 	AC_CHECK_FUNCS([issetugid])
+	case "$host_os" in
+	kfreebsd*-gnu | gnu*)
+		have_getpeereid=no
+		AC_CHECK_LIB(bsd, getpeereid, have_getpeereid=yes)
+		if test "x$have_getpeereid" = "xyes"; then
+			AC_DEFINE([HAVE_GETPEEREID], [1], [have getpeereid])
+			AC_SEARCH_LIBS([getpeereid], [bsd])
+		fi
+	;;
+	esac
 
 	AC_CACHE_CHECK([for thread-local storage class],
 		[ac_cv_tls_keyword],

--- a/common/unix-peer.c
+++ b/common/unix-peer.c
@@ -47,6 +47,11 @@
 #  include <ucred.h>
 #endif
 
+#ifdef HAVE_GETPEEREID
+/* Declare getpeereid from /usr/include/bsd/unistd.h */
+extern int getpeereid(int s, uid_t *euid, gid_t *egid);
+#endif
+
 /* Returns the unix domain socket peer information.
  * Returns zero on success.
  */
@@ -73,7 +78,8 @@ p11_get_upeer_id (int cfd, uid_t *uid, u
 		*pid = cr.pid;
 
 #elif defined(HAVE_GETPEEREID)
-	/* *BSD/MacOSX */
+	/* *BSD/MacOSX/kFreeBSD/Hurd */
+
 	uid_t euid;
 	gid_t egid;
 fs</a><a class='active' href='/guix/log/etc/completion'>log</a><a href='/guix/tree/etc/completion?id=e689bfe230a4ced09eb295045c3804d394356ab1'>tree</a><a href='/guix/commit/etc/completion?id=e689bfe230a4ced09eb295045c3804d394356ab1'>commit</a><a href='/guix/diff/etc/completion?id=e689bfe230a4ced09eb295045c3804d394356ab1'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/etc/completion'>
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<div class='path'>path: <a href='/guix/log/?id=e689bfe230a4ced09eb295045c3804d394356ab1'>root</a>/<a href='/guix/log/etc?id=e689bfe230a4ced09eb295045c3804d394356ab1'>etc</a>/<a href='/guix/log/etc/completion?id=e689bfe230a4ced09eb295045c3804d394356ab1'>completion</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/etc/completion?id=e689bfe230a4ced09eb295045c3804d394356ab1&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-12-04 23:45:08 +0100'>2020-12-04</span></td><td><a href='/guix/commit/etc/completion?id=611ae310f4ca1d93600c280e940a69b07e20c350'>bash completion: Complete file names after '-f' and '-l'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* etc/completion/bash/guix (_guix_is_dash_f, _guix_is_dash_l): New
functions.
(_guix_complete): Complete file names after 'guix package -f', 'guix
build -f', and 'guix environment -l'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-09-24 17:53:02 +0200'>2020-09-24</span></td><td><a href='/guix/commit/etc/completion?id=8e0c5033b17fcf1e4596ee9a3d52157900acc6fa'>bash completion: Adjust to new 'guix help' output.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is a followup to 3794ce93be8216d8378df7b808ce7f53b1e05a53, which
broke command completion.

Reported by Oleg Pykhalov &lt;go.wigust@gmail.com&gt;.

* etc/completion/bash/guix (_guix_complete_command): Update to match
output of 'guix help' as introduced in
3794ce93be8216d8378df7b808ce7f53b1e05a53.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-09-21 23:33:49 +0200'>2020-09-21</span></td><td><a href='/guix/commit/etc/completion?id=92951bf46c42021f6f6521839c9c4ff2f88b8386'>bash completion: Complete file names after 'guix package -p'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* etc/completion/bash/guix (_guix_complete): Add _guix_is_dash_p.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Fulbert</td></tr>
<tr><td><span title='2020-09-10 12:27:24 +0200'>2020-09-10</span></td><td><a href='/guix/commit/etc/completion?id=2ba81afcc204024255ce548e2c4cc4aed5541093'>bash completion: Restore completion for 'guix system', etc.</a><span class='msg-avail'>...<span class='msg-tooltip'>Commit 538ca8dd65f0075cc65bcca18ed87f66a789290a introduced a second
'_guix_complete_subcommand' function, shadowing the existing one, which
broke sub-command completion for 'guix system', 'guix import', etc.

* etc/completion/bash/guix: Distinguish between '_guix_complete_command'
and '_guix_complete_subcommand'.  Adjust users to call the right one.
</span></span></td><td>Ludovic Courtès</td></tr>