I have a PC with SSH server installed and often connect to it from my netbook (both running Sid) with X forwarding enabled. Since the other day when I connect to the PC I receive the message "X11 forwarding request failed on channel 0" and X forwarding no longer works.
On the host Pc I see the following in auth.log:I read around and saw mention that adding "AddressFamily inet" to sshd_conf solved this for some people but I still have the same problem after adding it.
I also tried running "xhost +" from the host PC but this has had no effect either.
I recall I struggled to set up X forwarding in the first place as I'm not at all familiar with setting it up so if anyone has any suggestions of anything else I could try I would be very grateful.

I found this:
it is a known bug from openssh. You can prove and see the reason, when you start sshd in debug modus: it tries to open several hundreds unix-sockets till it reaches a limit.
and also I found the following tips here: http://dbaspot.com/solaris/397531-s1...g-problem.html
disable ipv6 in general
add AddressFamily inet" to sshd_config
add "X11UseLocalhost no" to sshd_config
set IPv4 explicitly in sshd_config
and also found this comment: "if on the remote host I touch hostname6.lo0 I get the remote display."

I know that is and old solaris thread, but maybe you can try some of them (if not yet done). I'm really interested if it was a such an old bug in openssh.

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Thanks, adding "X11UseLocalhost no" seems to work (I don't see the error) but when trying to open an application I receive the error "Error: Can't open display: netbook:10.0" and the application doesn't open. I tried the -4 option on the client too but that doesn't change anything.
I don't know how to set the IP6 options mentioned.
I do wonder if this is possibly an X permissions issue and there's something simple I'm missing.

The can't open display message is a good news I think. The connection is ok, you have an authentication problem. Maybe the sshd is run by root and it has no right to access your display (or something similar)

My apologies, the error was "Error: Can't open display: PC:10.0". I tried running "xhost +" after the error and reconnecting but I still receive the same error.

where did you execute xhost +?

On the PC (the server) initially but now I've executed it on both and with the same error (Error: Can't open display: PC:10.0) as a result.

can you check if the port is opened or the ssh channel is available? (so it is a problem with ssh or with X)

I'm not sure what you mean? I can SSH into the PC fine, it's just X forwarding that's failing. I've no firewall or anything installed on the PC or netbook and X forwarding works the other way.

usually X server opens a port for every display.
:0 will be listening on 6000, :1 on 6001, .... :10 on 6010.
So when you create X forwarding ssh will open the port 6010 on your PC and forwards to port 6000 on your laptop.

When I run netstat I'm seeing this:so I think the port's open.

that is fine, so it means it should be an x authentication or security problem. Try ssh -X and ssh -Y, see the man page of ssh, maybe you will find it.

I've tried both X and Y options to the same effect. My problem is I have no idea how to solve an X authentication issue "xhost +" is about as much as I know how to do.

Where did you the ssh command executed from?

I'm executing ssh on my netbook to connect to my PC.