analyze-verify: honour $SYSTEMD_UNIT_PATH, allow system paths to be ignored

SYSTEMD_UNIT_PATH=foobar: systemd-analyze verify barbar/unit.service
will load units from barbar/, foobar/, /etc/systemd/system/, etc.

SYSTEMD_UNIT_PATH= systemd-analyze verify barbar/unit.service
will load units only from barbar/, which is useful e.g. when testing
systemd's own units on a system with an older version of systemd installed.

2 files changed, 23 insertions, 11 deletions

diff --git a/man/systemd-analyze.xml b/man/systemd-analyze.xml
index bc37765dff..8fa7cd3329 100644
--- a/man/systemd-analyze.xml
+++ b/man/systemd-analyze.xml
@@ -181,14 +181,15 @@
     <option>--log-target=</option>, described in
     <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>).</para>
 
-    <para><command>systemd-analyze verify</command> will load unit
-    files and print warnings if any errors are detected. Files
-    specified on the command line will be loaded, but also any other
-    units referenced by them. This command works by prepending the
-    directories for all command line arguments at the beginning of the
-    unit load path, which means that all units files found in those
-    directories will be used in preference to the unit files found in
-    the standard locations, even if not listed explicitly.</para>
+    <para><command>systemd-analyze verify</command> will load unit files and print
+    warnings if any errors are detected. Files specified on the command line will be
+    loaded, but also any other units referenced by them. The full unit search path is
+    formed by combining the directories for all command line arguments, and the usual unit
+    load paths (variable <varname>$SYSTEMD_UNIT_PATH</varname> is supported, and may be
+    used to replace or augment the compiled in set of unit load paths; see
+    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
+    All units files present in the directories containing the command line arguments will
+    be used in preference to the other paths.</para>
 
     <para>If no command is passed, <command>systemd-analyze
     time</command> is implied.</para>
diff --git a/src/analyze/analyze-verify.c b/src/analyze/analyze-verify.c
index 5fd3ee49eb..0ce0276d92 100644
--- a/src/analyze/analyze-verify.c
+++ b/src/analyze/analyze-verify.c
@@ -71,6 +71,7 @@ static int prepare_filename(const char *filename, char **ret) {
 }
 
 static int generate_path(char **var, char **filenames) {
+        const char *old;
         char **filename;
 
         _cleanup_strv_free_ char **ans = NULL;
@@ -90,9 +91,19 @@ static int generate_path(char **var, char **filenames) {
 
         assert_se(strv_uniq(ans));
 
-        r = strv_extend(&ans, "");
-        if (r < 0)
-                return r;
+        /* First, prepend our directories. Second, if some path was specified, use that, and
+         * otherwise use the defaults. Any duplicates will be filtered out in path-lookup.c.
+         * Treat explicit empty path to mean that nothing should be appended.
+         */
+        old = getenv("SYSTEMD_UNIT_PATH");
+        if (!streq_ptr(old, "")) {
+                if (!old)
+                        old = ":";
+
+                r = strv_extend(&ans, old);
+                if (r < 0)
+                        return r;
+        }
 
         *var = strv_join(ans, ":");
         if (!*var)