[SOLVED] X11 export display drops display

armageddonlord · 08-14-2018, 10:07 AM

I'm exporting my display from a remote system, to a local system. At first it works fine, but after about 20 minutes exported windows start to disappear, and attempting to open new windows give me errors like:

Code:

Error: Can't open display: localhost:10.0

I'm creating the connection with:

Code:

ssh -X ubuntuvm

and export display gets set correctly on the remote system:

Code:

env |grep DISPLAY
DISPLAY=localhost:10.0

I'm looking for:
A) remediation: How to reconnect the disconnected display while still in the same ssh session.
B) prevention: What is the cause, and how to prevent the disconnection in the first place.

remote/guest system:

Ubuntu 18.04
OpenSSH_7.6p1 Ubuntu-4, OpenSSL 1.0.2n 7 Dec 2017
xorg-server 1.19.6
running under VirtualBox 5.2.16

local/host system:

MacOS 10.13.6
homebrew 1.6.9
xquartz 2.7.11 (xorg-server 1.18.4)
OpenSSH_7.6p1, LibreSSL 2.6.2

network:

VirtualBox Host-only Adapter

business_kid · 08-16-2018, 04:12 AM

Is one of the screens blanking as they do to save power?

armageddonlord · 08-16-2018, 01:14 PM

Quote:

Originally Posted by business_kid

Is one of the screens blanking as they do to save power?

Nope. Power save is set for 3 hours, and this happens while I'm actively using the system.

armageddonlord · 01-16-2019, 10:10 AM

Use ssh -Y instead of -X, or update your ssh_config file. The default ForwardX11Timeout for the X11 SECURITY extension restrictions is 20 minutes.

Code:

SSH(1)
     -X      Enables X11 forwarding.  This can also be specified on a per-host basis in a configuration file.

             X11 forwarding should be enabled with caution.  Users with the ability to bypass file permissions on the
             remote host (for the user's X authorization database) can access the local X11 display through the for‐
             warded connection.  An attacker may then be able to perform activities such as keystroke monitoring.

             For this reason, X11 forwarding is subjected to X11 SECURITY extension restrictions by default.  Please
             refer to the ssh -Y option and the ForwardX11Trusted directive in ssh_config(5) for more information.

     -Y      Enables trusted X11 forwarding.  Trusted X11 forwardings are not subjected to the X11 SECURITY extension
             controls.

Code:

SSH_CONFIG(5)
     ForwardX11Timeout
             Specify a timeout for untrusted X11 forwarding using the format described in the TIME FORMATS section of
             sshd_config(5).  X11 connections received by ssh(1) after this time will be refused.  Setting
             ForwardX11Timeout to zero will disable the timeout and permit X11 forwarding for the life of the connec‐
             tion.  The default is to disable untrusted X11 forwarding after twenty minutes has elapsed.