Untrusted SSH clients or Gdk-WARNING **: Connection to display localhost:10.0 appears to be untrusted

While connecting to a local RH system via 'ssh -X' I was seeing errors like:

Connection to display localhost:10.0 appears to be untrusted. Pointer and 

keyboard grabs and inter-client communication may not work as expected.

OpenSSH implements the X11 SECURITY extension that provides two clients types: trusted & untrusted.

Trusted clients can do anything with the display while untrusted clients cannot inject synthetic events (mouse movement, keypresses, etc.) or read data from other windows (e.g. take screenshots).

In theory you should be able to run most applications via the untrusted category but it seems that a fair amount of client apps still do not implement this correctly so YMMV.

If you want to initialize a SSH connection with X11 forwarding support and using the trusted security type you simply replace -X with -Y:

$ ssh -Y USER@HOST

TIP: Add a '-C' to your ssh connections to speed things up. Nothings for free but I am sure the CPU/speed trade-off will suit most users.

ssh-agent for Developers

Have you ever wanted to automate the ssh pass phrase login procedure when connecting to remote systems that have your public key in their .ssh/authorized_keys?

This is done using ssh-agent (and ssh-add) which will be on your Debian or Ubuntu system if you have the openssh-client dep installed. For other flavours of Linux, OS X or UNIX please refer to your package management documentation (or install from source) to see how you can install the required software.

On an Ubuntu system ssh-agent is started for you by default. Please refer to your system documentation for ssh-agent to find the correct way to run it on your system.

The following approach should work for situations where the client (the computer with the private key) is either a server (access is generally restricted to it via remote shell) or a desktop (includes laptops) with a graphical terminal program.

Add the following to the end of your ~/.bashrc (or other suitable shell setup configuration file):

# Run ssh-add if it has not been run already.
if  ssh-add -l | grep -q 'The agent has no identities.'
then
eval "ssh-add"
fi

Save the addition to your .bashrc (or suitable alternative) and log out and back in.

You will be presented with a request for your pass phrase you chose when creating your public/private keys. Enter it and sigh with relief as your default key(s) are cached in memory.

When you now try and log into the remote system again there will be no passwords or pass phrases required for this session.