Print better error message when exec fails

dumb-init.c

@@ -132,9 +132,8 @@ int main(int argc, char *argv[]) {
         // if this point is reached, exec failed, so we should exit nonzero
         fprintf(
             stderr,
-            "Failed to launch process '%s' (errno %d: %s)\n",
+            "dumb-init: %s: %s\n",
             argv[1],
-            errno,
             strerror(errno)
         );
         exit(2);

tests/child_processes_test.py

@@ -131,6 +131,6 @@ def test_fails_nonzero_with_bad_exec(both_debug_modes, both_setsid_modes):
     proc.wait()
     assert proc.returncode != 0
     assert (
-        "Failed to launch process '/doesnotexist' (errno 2: No such file or directory)\n"
+        'dumb-init: /doesnotexist: No such file or directory\n'
         in proc.stderr
     )