[Bug 657302] [NEW] X11 forwarding does not work

[LGB [Gábor Lénárt]]

Public bug reported:

I have problems with X11 forwarding via SSH both with lucid and maverick. On both of these systems it simply does not work
saying (for example):

xterm Xt error: Can't open display: 
xterm:  DISPLAY is not set

In /var/log/auth.log I can find this:

Oct  9 13:46:45 oxygene sshd[11122]: error: Failed to allocate internet-
domain X11 display socket.

After trying to strace the sshd process, I found things like this:

11122 bind(10, {sa_family=AF_INET6, sin6_port=htons(6010),
inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0,
sin6_scope_id=0}, 28) = -1 EADDRNOTAVAIL (Cannot assign requested
address)

It's strange for me, since I've disabled IPv6 everywhere, but still it
want to use it for some unknown reason ...

I even have -4 option in /etc/default/ssh but it does not help.

HOWEVER, if I stop ssh daemon and launch it "by hand" /usr/sbin/sshd -4
then it works nicely! It's interesting that init script (or upstart?)
script of sshd does not honor /etc/default/ssh it seems ... Or it
shouldn't do that in maverick anymore?

Yes, I know that problem is caused not having IPv6 in my system by will,
but I haven't known that I am forced to have configured IPv6 it was not
compulsory in previous versions of Ubuntu distros. Is it possible to use
Ubuntu in a normal way (without dirty hacks) if I don't want IPv6 at
all? On my network there is no IPv6 capable equipment, so it's totally
pointless to have it for any reason but still it does introduces
possible security holes etc, I think the best practice not to have
_anything_ configured which is not used/needed to avoid resource wasting
and maybe even security problems. Like in OpenBSD where the default
install is very minimal that's why that only 2 remote holes in the
default install since X ages :) :)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:1777 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1777 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:6642772 (6.6 MB)  TX bytes:6642772 (6.6 MB)

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: openssh-server 1:5.5p1-4ubuntu4
ProcVersionSignature: Ubuntu 2.6.35-22.33-generic 2.6.35.4
Uname: Linux 2.6.35-22-generic i686
NonfreeKernelModules: nvidia
Architecture: i386
Date: Sat Oct  9 13:52:29 2010
EcryptfsInUse: Yes
ProcEnviron:
 LANGUAGE=en_US:en
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: openssh

** Affects: openssh (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: apport-bug i386 maverick

-- 
X11 forwarding does not work
https://bugs.launchpad.net/bugs/657302
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