Looks like I've faced something similar to this bug, and seems that it is caused by incorrect choice of dispaly number by remote sshd.
Look: [EMAIL PROTECTED]:~> ssh -X sercond No mail. [EMAIL PROTECTED]:~> echo $DISPLAY localhost:10.0 [EMAIL PROTECTED]:~> xterm xterm Xt error: Can't open display: localhost:10.0 However, at this point there already exists an ssh connection to 'sercond' host from different host, with X11 forwarding enabled, that uses display 10! [EMAIL PROTECTED]:~> ssh -x sercond No mail. [EMAIL PROTECTED]:~> echo $DISPLAY [EMAIL PROTECTED]:~> sudo netstat -lapn | grep 6010 tcp 0 0 127.0.0.1:6010 127.0.0.1:57566 ESTABLISHED1096/sshd: [EMAIL PROTECTED] tcp 0 0 127.0.0.1:57566 127.0.0.1:6010 ESTABLISHED1099/kmix So for unknown reason, new ssh connection to sercond does not detect that :0 is already in use there. So running X client actually tries to connect to different display, and that connections is naturaly rejected. If I connect one more connection with -X from 'bliss' to 'sercond', while keeping older -X connection active, new connection gets dispaly 11, and X forwarding works. I was able to reproduce problem from clear. - shutdown all ssh connections - try to connect from 'bliss' to 'sercond', X11 forwadring works - shutdown connection from 'bliss' to 'sercond' - set up connection from 'blacky' to 'sercond' - try to connect rom 'bliss' to 'sercond' once more - X11 forwarding does not work, because it tries to use display 10 on 'sercond' that is already occupied by connection from 'blacky'. blacky has: ii libx11-6 6.9.0.dfsg.1-6 ii openssh-client 4.2p1-8 ii openssh-server 4.2p1-8 bliss has: ii libx11-6 1.0.0-6 ii openssh-client 4.2p1-8 ii openssh-server 4.2p1-8 sercond has: ii libx11-6 6.9.0.dfsg.1-4 ii openssh-client 4.2p1-8 ii openssh-server 4.2p1-8
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