openssh: ssh X11 forwarding is degraded

[thomas]

Sice a couple of months forwarded X applications show a considerable lag, a) when opening an application, and b) when running it. It can take up to 5 seconds until a new terminal window opens.

In simple terminals it is not so obvious (after the initial wait), but even the rather modest nedit shows extreme lags on construction, and when using the file-open dialog.

How to check?

This can be observed on a single host, ruling out network issues:

  #> ssh $HOSTNAME
  #> nedit  #  [Ctrl]-[O]

It should lag...

Two ways to further confirm:

a) downgrade to openssh-9.3_p2-0.x86_64

  #> bee update -f openssh-9.3_p2-0.x86_64

reboot (or simply restart openssh ? - not tested) - No lag anymore ...

b) bypass ssh forwarding

Edit /etc/lightdm/lightdm.conf, in the seat section allow tcp connctions to the X server.

   [Seat:*]
 + xserver-allow-tcp=true
 + xserver-command=X -listen tcp

Restart lightdm

  #> systemctl restart lightdm

then, when logged in again ...

  #> ssh $HOSTNAME
  #> nedit  #  [Ctrl]-[O]

It should lag... [Ctrl]-[D]

Now connect the 'old fashioned' way

  #> xhost +   
  #> ssh $HOSTNAME
  #> nedit -display $HOSTNAME:0.0 #  [Ctrl]-[O]

No lag ...
xhost + may be unneeded when you stay on your machine

The file https://www.openssh.com/releasenotes.html is way long, but searchin for 'lagging X11 ssh forwarding' is a more or less hopeless endeavour I guess.

Any ideas ?

[thomas]

I can not tell if I ever saw a more ridiculous feature change in ssh :)

ssh 9.5 has a new default feature, you may read:
| https://www.serice.net/ObscureKeystrokeTiming.html
... what saves me the typing

Two of the possible solutions include:
a) use a client from before 9.5
b) ssh -o ObscureKeystrokeTiming=no whatever

[thomas]

And this is aparently one root of all the fuzz:
https://www.usenix.org/legacy/events/sec01/full_papers/song/song.pdf

Q: why does ssh use keystroke jitter when I authenticate via public key?

[donald]

Why did you close? Shouldn't we disabled this misfeature by default on Mariux64?

[donald]

Fixed by mariux64/mxtools#417