The setuid helper of D-Bus is responsible for "service activation".
It looks for '.service' files in fixed locations, but the default locations
make no sense (see below), so replace them with /etc/dbus-1/system-services.

--- dbus-1.10.0/dbus/dbus-sysdeps-util-unix.c	2015-10-22 00:07:03.829251854 +0200
+++ dbus-1.10.0/dbus/dbus-sysdeps-util-unix.c	2015-10-22 00:07:14.893445175 +0200
@@ -1410,10 +1410,7 @@ _dbus_get_standard_system_servicedirs (D
    * be available.
    */
   static const char standard_search_path[] =
-    "/usr/local/share:"
-    "/usr/share:"
-    DBUS_DATADIR ":"
-    "/lib";
+    "/etc";
   DBusString servicedir_path;
 
   _dbus_string_init_const (&servicedir_path, standard_search_path);

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<div class='path'>path: <a href='/guix/log/?id=dbdd77074a2f45f2967cf20733b8111ce4df2c16'>root</a>/<a href='/guix/log/tests?id=dbdd77074a2f45f2967cf20733b8111ce4df2c16'>tests</a>/<a href='/guix/log/tests/syscalls.scm?id=dbdd77074a2f45f2967cf20733b8111ce4df2c16'>syscalls.scm</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/tests/syscalls.scm?id=dbdd77074a2f45f2967cf20733b8111ce4df2c16&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-10-05 22:05:02 +0200'>2019-10-05</span></td><td><a href='/guix/commit/tests/syscalls.scm?id=5e5f7167943b408ae55736a44908a82056c87780'>syscalls: Add 'add-to-entropy-count'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/build/syscalls.scm (RNDADDTOENTCNT): New variable.
(add-to-entropy-count): New procedure.
* tests/syscalls.scm ("add-to-entropy-count"): New test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-06-27 11:14:40 +0200'>2019-06-27</span></td><td><a href='/guix/commit/tests/syscalls.scm?id=4593f5a654b4e59c5025cc4f99914e24e82515a4'>syscalls: Add 'terminal-rows'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/build/syscalls.scm (terminal-dimension): New procedure.
(terminal-columns): Rewrite in terms of 'terminal-dimension'.
(terminal-rows): New procedure.
* tests/syscalls.scm ("terminal-rows"): New test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-07-03 17:50:04 +0200'>2018-07-03</span></td><td><a href='/guix/commit/tests/syscalls.scm?id=25c7ff6a3ecbaa1e93b38d35c8cbff40b7f4edb8'>syscalls: Define AT_SYMLINK_NOFOLLOW et al.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/build/syscalls.scm (AT_FDCWD, AT_SYMLINK_NOFOLLOW, AT_REMOVEDIR)
(AT_SYMLINK_FOLLOW, AT_NO_AUTOMOUNT, AT_EMPTY_PATH): New variables.
* tests/syscalls.scm ("utime with AT_SYMLINK_NOFOLLOW"): New test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-04-08 17:41:08 +0200'>2018-04-08</span></td><td><a href='/guix/commit/tests/syscalls.scm?id=6ef80eb0d94181eb5f755a11fca0d428252ce753'>tests: Skip 'pivot-root' test on Ubuntu's 4.4 kernels.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/25476&gt;.
Reported by Paul Garlick &lt;pgarlick@tourbillion-technology.com&gt;
and Maria Sidorova &lt;hydromasha@gmail.com&gt;.

* tests/syscalls.scm ("pivot-root"): Skip on known-bad Ubuntu kernels.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-11-25 18:12:33 +0100'>2017-11-25</span></td><td><a href='/guix/commit/tests/syscalls.scm?id=4aac8d059a2bec9f075ceea2a089ca029a71912c'>syscalls: Adjust utmpx test.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/29426&gt;.
Reported by Adonay Felipe Nogueira &lt;adfeno@hyperbola.info&gt;.

* tests/syscalls.scm ("utmpx-entries"): Check the value
of (utmpx-entries entry) only for INIT_PROCESS, LOGIN_PROCESS, and
USER_PROCESS entries.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-07-12 16:15:30 +0200'>2017-07-12</span></td><td><a href='/guix/commit/tests/syscalls.scm?id=0bc6fe323d34aabc7f51fa80b8872a2c1770d32a'>syscalls: Add network-interface-running?</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/build/syscalls.scm (network-interface-running?): New variable.
Export it.
* tests/syscalls.scm: Add test.

Co-authored-by: John Darrington &lt;jmd@gnu.org&gt;
</span></span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2017-06-16 17:08:22 +0200'>2017-06-16</span></td><td><a href='/guix/commit/tests/syscalls.scm?id=fa73c1937364872560c509f02b3d7648a5bed006'>syscalls: Add 'scandir*'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/build/syscalls.scm (%struct-dirent-header): New C struct.
(string-&gt;pointer/utf-8, pointer-&gt;string/utf-8): New procedures.
(opendir*, closedir*, readdir*, scandir*): New procedures.
* tests/syscalls.scm ("scandir*, ENOENT")
("scandir*, ASCII file names", "scandir*, UTF-8 file names")
("scandir*, properties): New tests.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-05-28 23:13:39 +0200'>2017-05-28</span></td><td><a href='/guix/commit/tests/syscalls.scm?id=aa401f9ba6410095370ce0c4e5a01c02203a2b9f'>syscalls: Add 'thread-name' and 'set-thread-name'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/build/syscalls.scm (PR_SET_NAME, PR_GET_NAME)
(%max-thread-name-length): New variables.
(%prctl, set-thread-name, thread-name): New procedures.
* tests/syscalls.scm ("set-thread-name"): New test.
</span></span></td><td>Ludovic Courtès</td></tr>