Change test for ControlPath in order to avoid DNS timeouts.

Fixes: debbugs:20015

* net/tramp-sh.el (tramp-ssh-controlmaster-options): Change test
for ControlPath in order to avoid DNS timeouts.

2 files changed, 11 insertions, 2 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index cbd1bce25e8..96478223d49 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2015-03-17  Michael Albinus  <michael.albinus@gmx.de>
+
+        * net/tramp-sh.el (tramp-ssh-controlmaster-options): Change test
+        for ControlPath in order to avoid DNS timeouts.  (Bug#20015)
+
 2015-03-16  Alan Mackenzie  <acm@muc.de>
 
         Edebug: Allow "S" to work during trace mode.  Fixes debbugs #20074.
diff --git a/lisp/net/tramp-sh.el b/lisp/net/tramp-sh.el
index 73ad8c7e4ef..b6c47bcb7bb 100644
--- a/lisp/net/tramp-sh.el
+++ b/lisp/net/tramp-sh.el
@@ -4565,7 +4565,7 @@ Gateway hops are already opened."
 
     ;; In case the host name is not used for the remote shell
     ;; command, the user could be misguided by applying a random
-    ;; hostname.
+    ;; host name.
     (let* ((v (car target-alist))
            (method (tramp-file-name-method v))
            (host (tramp-file-name-host v)))
@@ -4611,9 +4611,13 @@ Gateway hops are already opened."
                 (setq tramp-ssh-controlmaster-options "-o ControlMaster=auto")))
             (unless (zerop (length tramp-ssh-controlmaster-options))
               (with-temp-buffer
+                ;; When we use a non-existing host name, we could run
+                ;; into DNS timeouts.  So we use "localhost" with an
+                ;; improper port, expecting nobody runs sshd on the
+                ;; telnet port.
                 (tramp-call-process
                  vec "ssh" nil t nil
-                 "-o" "ControlPath=%C" "host.does.not.exist")
+                 "-p" "23" "-o" "ControlPath=%C" "localhost")
                 (goto-char (point-min))
                 (setq tramp-ssh-controlmaster-options
                       (if (search-forward-regexp "unknown.+key" nil t)