# SSH session hang on starting GUI program with X11 forwarding

## lowsfer

Hi guys,

I'm experiencing a problem with starting GUI program via ssh with x11 forwarding. Every time the ssh session just hang. Then I have to "killall ssh" to end the SSH session. Tried both "-X" and "-Y", none worked.

I tried debug mode of ssh "ssh -Xvvv username@host"

when I start xterm, I got the following debug info:

```

debug1: client_input_channel_open: ctype x11 rchan 3 win 65536 max 16384

debug1: client_request_x11: request from ::1 57420

debug2: fd 7 setting O_NONBLOCK

debug3: fd 7 is O_NONBLOCK

debug1: channel 1: new [x11]

debug1: confirm x11

```

Other relevant info:

```

>echo $DISPLAY

localhost:14.0

```

All non-comment content of /etc/ssh/ssh_config on my local machine (ssh client / X11 server)

```

Host *

    XAuthLocation /usr/bin/xauth

    ForwardX11 yes

    ForwardX11Trusted yes

```

I believe the settings on the ssh server/X11 client machine are OK because I can use X11 forwarding on another windows machine with putty+Xming perfectly.

Does anyone know what is the problem? Thanks.

----------

## lowsfer

Solved the problem finally!

It's the problem with vpn. I was using ssh over vpn. And it's a classic MTU problem. To solve it, excute 

```

ifconfig tun0 mtu 1350

```

after making vpn connection.

----------

