can't communicate fully with other computers

[snowmanwx]

I downloaded and installed a new copy of Fedora 11 last week onto a new computer (hereafter "proximate"). I also have a remote computer without a monitor running an outdated version of Red Hat Linux (hereafter "remote"). To manage the processes on remote graphically, I ssh from proximate into remote; this connection succeeds without incident in transmitting text (including commands) between the two computers; however, the command "gnome-session" returns:

(gnome-session:15789): Gtk-WARNING **: cannot open display:

(The numbers apparently represent the process identifier and vary from instance to instance.) A similar warning (and no accompanying graphics) occurs whenever I attempt to start any graphical user interface from remote via ssh from proximate. The issue almost certainly lies with proximate; remote successfully communicated graphics to the ancient box that proximate replaces.

Interestingly, I cannot communicate via ssh from remote to proximate (within a secure shell from proximate to remote). If I execute /usr/sbin/sshd on proximate as root, then I can login, but even then I cannot execute any commands.

Consider the following output:

[snowmanwx@proximate ~]$ su
Password:
[root@proximate jpetre]# ssh remote
root@remote's password:
Last login: Mon Oct 19 12:10:22 2009 from proximate
[root@aqmodel ~]# gnome-session

(gnome-session:15879): Gtk-WARNING **: cannot open display:
[root@remote ~]# ssh proximate
root@proximate's password:
Last login: Mon Oct 19 18:24:58 2009 from remote
Connection to proximate closed.
[root@remote ~]#


If I execute ssh -vvv proximate from remote to proximate, then I get a lengthy output that ultimately ends with "debug1: Exit status 254."



What must I do to communicate both text and graphics among my computers? Thank you for any assistance.

[snowmanwx]

I apparently (at least partially and incipiently) resolved the issue with ssh from proximate to remote and thence back to proximate . The solution involves changing settings to enable ssh in system-config-selinux (accessible via System > Administration > SELinux Management). Under "Status," I changed the enforcing mode to "permissive," and under "Boolean," I checked "active" beside both "ssh" modules. I'm not sure why it worked, but that's conceivably a potential solution.

The gnome-session error unfortunately yet remains, and the two errors therefore apparently aren't connected.

[jpollard]

Do the following:
First verify that the sshd configuration on the server allows X window forwarding. If it is commented
out or disabled enable it:

/etc/ssh/sshd_conf
...
#AllowAgentForwarding yes
#AllowTcpForwarding yes
#GatewayPorts no
#X11Forwarding no <---- shows the default
X11Forwarding yes <---- enable X11 forwarding
#X11DisplayOffset 10
#X11UseLocalhost yes
#PrintMotd yes
....

Restart the sshd service:
service sshd restart

You may also need to change firewall configuration to permit incoming ssh, but I suspect you
already have that.

Now on the workstation/whatever connect to the remote server with:

ssh -X remote

After connecting verify that you have an X display defined:

echo $DISPLAY

The result should be: "localhost:10.0" or something similar (10.0 is the first display,
11.0 should be the second... depending on how many connections there are).

The default sshd configuration is to not forward X sessions. A problem you MAY have with
you gnome-session is that you do not truly have a session. When you login on the workstation, you
are starting a session. A remote login to another system does not alter that since you are forwarding
X connections to your workstation (with a gnome session already active). Trying to start a second
session SHOULD give you an error (though I don't know exactly what the error would be). If I run
the "twm" window manager while logged in using gnome I get:

$ twm
twm: another window manager is already running. on screen 0?
twm: unable to find any unmanaged video screens.
$

The error is caused by the fact that a window manager is already connected to your X server, and
will conflict with another window manager. Usually when this happens to me I see something like
"window manager already active" and then the application exits.

You can however, run other applications - some that may have a problem are gnome applets and
such, since they may depend on local window manager support, but who knows.

[snowmanwx]

wow, jpollard. I am such a dunce. Your solution works perfectly. Thanks. I didn't think it would come so soon.