On Feb 18, 2006, at 10:47 AM, Ron Yorston wrote:
> Tony Schreiner <schreian@xxxxxx> wrote:
>> I'm trying to run an application (rasmol - molecule viewing program)
>> which when using the the default setup for x11 forwarding causes the
>> following error:
>>
>> X Error of failed request: BadAccess (attempt to access private
>> resource denied)
>> Major opcode of failed request: 132 (MIT-SHM)
>> Minor opcode of failed request: 1 (X_ShmAttach)
>> Serial number of failed request: 230
>> Current serial number in output stream: 231
>>
>>
>> It used to be possible to overcome this by setting
>>
>> X11UseLocalhost no
>>
>> in /etc/ssh/sshd_config
>>
>> This worked in CentOS 3 but does not in CentOS 4 (or Fedora 4 for
>> that matter), and I'm guessing it is a XFree86 vs. Xorg issue.
>>
>> Now, when using
>> X11UseLocalhost no
>>
>> no X applications work
>>
>> ssh myserver
>> # echo $DISPLAY
>> myserver.fqdn:10.0
>> # xdpyinfo
>> xdpyinfo: unable to open display "myserver.fqdn:10.0".
>
> It appears that in FC4 setting 'X11UseLocalhost no' causes sshd to
> listen
> for X connections only on the IPV6 port:
>
> $ netstat -ant | grep 6010
> tcp 0 0 :::
> 6010 :::* LISTEN
>
> I'd say this was a bug, and indeed there is such a report in the
> openssh
> bugzilla, but it's supposed to have been fixed years ago. I've tried
> forcing sshd to use IPV4 only (with the -4 flag) but that just gets me
> back into the land of X authentication failures.
>
> The problem with rasmol is that it tries to use the X shared memory
> extension
> if it thinks it's running on the same host as the X server. To
> rasmol an
> ssh-forwarded X connection looks like a local connection, so it
> tries to
> use shared memory and fails. The 'X11UseLocalhost no' trick works
> because
> it makes the forwarded connection look like a connection to a
> remote machine
> so the application falls back to using an alternative.
>
> Looking at the source for rasmol I see that it uses this test to
> determine
> if it can use MIT-SHM:
>
> ptr = DisplayString(dpy);
> if( !ptr || (*ptr==':') || !strncmp(ptr,"localhost:",10) ||
> !strncmp(ptr,"unix:",5) || !strncmp(ptr,"local:",6) )
>
> So even with 'X11UseLocalhost yes' it might be possible to fool it
> into not
> using MIT-SHM by setting your DISPLAY to '127.0.0.1:10.0' (or
> whatever).
>
> Ron
> _______________________________________________
Absolutely right. Thanks a million.
If I leave
X11UseLocahost yes
connect, and then explicitly change my DISPLAY to 127.0.0.1:10.0 (or
whatever), then the application runs.
And thanks for the confirmation abou X11UseLocalhost no.
Tony Schreiner
