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I ssh -X from Ubuntu to an Ubuntu Server, on which I've installed X, x11-apps and Firefox. Running xeyes shows the eyes, so I know that the X forwarding works. But when I try firefox, nothing happens: no window pops up, and the terminal line isn't returned until I ctrl+C.

How to debug this? I don't have physical access to the server.

ps aux shows:

me      22016  1.0  0.8  53464  9076 pts/1    S+   17:20   0:00 /usr/lib/firefox-10.0.2/firefox
me      22018  0.0  0.0      0     0 pts/1    Z+   17:20   0:00 [firefox] <defunct>

Update: After waiting for 8 min, a Firefox window popped up and worked fine, without lag or any other problems. So the new question is: why does it take so much time?

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Is this over internet or LAN or home wireless network (or something else)? If it's over the Internet, then that could explain it, especially if you've got a relatively slow connection. – zpletan Mar 13 '12 at 14:14
Could you try if compression helps (add -C to ssh command)? Firefox also tries to find and connect with an existing instance, does firefox -no-remote start up any faster? – taneli Mar 13 '12 at 20:17
You should try VNC for remote GUI applications – baptx Jul 25 '14 at 18:22

If you are tunnelling your X11 through ssh, you might want to add compression to the tunnel as well. This can increase performance if bandwidth is scarce.

for example something like this

ssh -CX -c blowfish yourname@yourhost
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Reading the man page of ssh, it came to my attention that the blowfish parameter belongs to the -c (lower c) parameter. You should use it without argument: ssh -X -C yourname@yourhost – panmari May 21 '13 at 7:41
yup updated my answer. – tomodachi May 23 '13 at 15:17

You may want to check the amount of data transmitted through the network and the bitrate. I like to use 'dstat 60' for that. ($ sudo apt-get install dstat). Check if you see a lot of network traffic on either side, server and client) and if the rate is anywhere near the network bandwidth available. Notice that WAN links, DSL lines, Internet may have lower bandwidth than your network interface.

Check the top command for a hight iowait percentage. Press 1 to view per core statistics. High numbers of iowait usually indicate your CPU is waiting for data from the disks.

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