Ah this is a unix command. yeah it exists in slackware too.
Didn't think of this. Still is there a way (that you know of) to prioritize ipv4 over ipv6 ?
for example I read that /etc/hosts file can lead to ipv6 resolution with priority if the ::1 entry is above the 127.0.0.1 one. But this is not the case in my case.

Alternatively, is it possible to tell the X server to prefer ipv4 over ipv6 ?


On Tue, Jan 20, 2026 at 10:43 AM Ulrich Sibiller <ulrich.sibiller@gmail.com> wrote:
Hi,

well, of course IPv4 should suffice. Maybe you should check if your
name resolution yields IPv6 addresses. No idea how slackware handles
this but there should be a straightforward way to disable IPv6. Using
firewall rules seems wrong to me.

In RedHat you can do this using sysctl and set
"net.ipv6.conf.all.disable_ipv6 = 1".

Uli

On Mon, Jan 19, 2026 at 11:23 PM Athanasios Silis
<athanasios.silis@gmail.com> wrote:
>
> Ok I have figured it out, but I don't think it should be like that.
>
> So I have completely disabled ipv6 on that laptop (policy is DROP for all chains INPUT, OUTPUT and FORWARD). No it did not even accept localhost connections in ipv6.
> Once I changed the firewall to accept local ipv6 connections (accept from localhost only and accept OUTgoing packets in output chain) things started working again.
>
> The question is. Shouldn't ipv4 suffice for all this to work ?
>
> This question has no practical value but I would very much like to understand why does ipv6 must be allowed internally.
>
> Thank you for your help Ulrich!
>
>
> On Mon, Jan 19, 2026 at 11:03 PM Athanasios Silis <athanasios.silis@gmail.com> wrote:
>>
>> hi Ulrich,
>> thank you for the quick response.
>> Definitely X11 systems across all the systems I admin - no wayland.
>>
>> The quick test does indeed create an nxagent window . It does delay unreasonably though for about 10seconds at some point.
>> Eventually it does continue and I do see the black/empty window eventually. You'll notice that the nxagent on the server side is (thankfully) Version 3.5.99.26.
>> Please note: the x2goserver resides on a slackware64-current system. But I have another reference system (slackware64-15.0) with the exact same x2goserver version.
>> The reference version works fine and running the same test there works fine too, but it does not "halt" at the moment when the problematic halts for about 10 seconds.
>>
>> OK so the log in the problematic system is as follows:
>>
>> nass@whitestar$ ssh blackstar -X
>> Last login: Mon Jan 19 22:37:27 2026 from 192.168.112.145
>> Linux 6.12.63.
>>
>> nass@blackstar:~$ nxagent :55
>>
>> NXAGENT - Version 3.5.99.26
>>
>> Copyright (c) 2001, 2011 NoMachine (http://www.nomachine.com)
>> Copyright (c) 2008-2014 Oleksandr Shneyder <o.shneyder@phoca-gmbh.de>
>> Copyright (c) 2011-2016 Mike Gabriel <mike.gabriel@das-netzwerkteam.de>
>> Copyright (c) 2014-2016 Ulrich Sibiller <uli42@gmx.de>
>> Copyright (c) 2014-2016 Mihai Moldovan <ionic@ionic.de>
>> Copyright (c) 2015-2016 Qindel Group (http://www.qindel.com)
>> See https://github.com/ArcticaProject/nx-libs for more information.
>>
>> Info: Agent running with pid '17964'.
>> Session: Starting session at 'Mon Jan 19 22:49:53 2026'.
>>
>> [It seemingly blocks for about 10seconds here. Then it continues...]
>>
>> Info: Using alpha channel in render extension.
>> Info: Not using local device configuration changes.
>> Warning: Cannot read keystroke file '/home/nass/.nx/config/keystrokes.cfg'.
>> Info: using keystrokes file '/etc/nxagent/keystrokes.cfg'
>> Currently known keystrokes:
>>   close_session         : Ctrl+Alt+t
>>   switch_all_screens    : Ctrl+Alt+f
>>   fullscreen            : Ctrl+Shift+Alt+f
>>   minimize              : Ctrl+Alt+m
>>   defer                 : Ctrl+Alt+e
>>   force_synchronization : Ctrl+Alt+j
>>   resize                : Ctrl+Alt+r
>>   viewport_move_left    : Ctrl+Shift+Alt+Left
>>   viewport_move_left    : Ctrl+Shift+Alt+KP_Left
>>   viewport_move_up      : Ctrl+Shift+Alt+Up
>>   viewport_move_up      : Ctrl+Shift+Alt+KP_Up
>>   viewport_move_right   : Ctrl+Shift+Alt+Right
>>   viewport_move_right   : Ctrl+Shift+Alt+KP_Right
>>   viewport_move_down    : Ctrl+Shift+Alt+Down
>>   viewport_move_down    : Ctrl+Shift+Alt+KP_Down
>>   viewport_scroll_left  : Ctrl+Alt+Left
>>   viewport_scroll_left  : Ctrl+Alt+KP_Left
>>   viewport_scroll_up    : Ctrl+Alt+Up
>>   viewport_scroll_up    : Ctrl+Alt+KP_Up
>>   viewport_scroll_right : Ctrl+Alt+Right
>>   viewport_scroll_right : Ctrl+Alt+KP_Right
>>   viewport_scroll_down  : Ctrl+Alt+Down
>>   viewport_scroll_down  : Ctrl+Alt+KP_Down
>>   reread_keystrokes     : Ctrl+Alt+k
>>   autograb              : Ctrl+Alt+g
>>   dump_clipboard        : Ctrl+Shift+Alt+c
>> error opening security policy file /usr/local/share/nx/SecurityPolicy
>> Info: Keycode conversion auto-determined as on
>> Session: Session started at 'Mon Jan 19 22:50:04 2026'.
>> Info: Screen [0] resized to geometry [1280x965] fullscreen [0].
>>
>> At this stage the nxagent window fired up in the server side, has been drawn in the client desktop environment as a separate window.
>>
>>
>>
>>
>> On Mon, Jan 19, 2026 at 9:42 PM Ulrich Sibiller <ulrich.sibiller@gmail.com> wrote:
>>>
>>> Hi,
>>>
>>> You are using nxproxy 3
>>> 5.99.23 which should not be a problem, despite being very old. But maybe you are also using this ancient version on the server. Which IS a problem. Please ensure you use 3.5.99.26 or 27.
>>>
>>> A quick test to rule out some things: ssh -X ro the server, then run nxagent :55. Do you see an nxagent window?
>>>
>>> Also, are you sure you have an X desktop running on the server and not wayland? And on the client?
>>>
>>> Uli
>>>
>>>
>>>
>>> Athanasios Silis <athanasios.silis@gmail.com> schrieb am Mo., 19. Jan. 2026, 19:34:
>>>>
>>>> Hi all,
>>>> I recently installed x2goserver (and x2goclient but this is probably not relevant in this case) on a fresh slackware-current system.
>>>>
>>>> Then, using x2goclients from other computers (other slackware64-15.0, ubuntu20.04 and 24.04 and debian systems) I want to "fetch" a desktop from this fresh system to one of the other client systems.
>>>>
>>>> The connection seems to go through normally but I never see a desktop window poping up. I have tried "xfce" and "fluxbox" (as a custom command) both of which have been faithfully working in the past and in other installations.
>>>>
>>>> I used `x2goclient --debug` to invoke the session and see if there are any meaningful messages error messages from the client side, but I have not been able to figure out if there is anything relevant:
>>>>
>>>>     $ x2goclient --debug
>>>>     qt5ct: using qt5ct plugin
>>>>     x2go-INFO-1> "Starting X2Go Client 4.1.2.2..."
>>>>     [...]
>>>>     x2go-INFO-3> "Started X2Go Client."
>>>>     [...]
>>>>     x2go-INFO-8> "Starting connection to server: x.x.x.x:22"
>>>>     [...]
>>>>     x2go-DEBUG-../src/sshmasterconnection.cpp:687> User authentication OK.
>>>>     [...]
>>>>     x2go-DEBUG-../src/sshmasterconnection.cpp:702> Login Check - OK
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:2947> SSH connection established.
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:3374> Continue normal X2Go session
>>>>     [...]
>>>>     x2go-DEBUG-../src/sshprocess.cpp:387> Starting tunnel via SshProcess object 2: "localhost":57842 -> "localhost":58842
>>>>     [...]
>>>>     x2go-DEBUG-../src/sshmasterconnection.cpp:2065> Executing remote: "bash -l -c 'echo \"X2GODATABEGIN:1790db9f-7b15-48ca-9eec-7596bdb1cccf\"; export PATH=\"/usr/local/bin:/usr/bin:/bin\";export TERM=\"dumb\"; X2GODPI=141 X2GO_XINERAMA=no x2gostartagent 800x600 adsl 16m-jpeg-9 unix-kde-depth_24 us auto 1 D startfluxbox both; echo \"X2GODATAEND:1790db9f-7b15-48ca-9eec-7596bdb1cccf\";'"
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:6142> "Starting NX proxy, command: nxproxy -S nx/nx,options=/home/user/.x2go/S-poker-50-1768844727_stDstartfluxbox_dp24/options:50"
>>>>     [...]
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:6618> Proxy wrote on stderr: "\nNXPROXY - Version 3.5.99.23\n\nCopyright (c) 2001, 2011 NoMachine[...]
>>>>         Info: Connecting to remote host 'localhost:58842'.\n
>>>>         Info: Connected to remote proxy on FD#5.\n"
>>>>
>>>>
>>>> So it seems ssh connection gets established, login is OK, `nxstartagent` is executed fine, and  `nxproxy` also starts without errors. but then
>>>>
>>>>
>>>>
>>>>     2go-DEBUG-../src/sshprocess.cpp:109> New TCP connection.
>>>>     x2go-DEBUG-../src/sshprocess.cpp:114> New socket: 21
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:11659> "Searching proxy window: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:13278> "Searching window with title: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     x2go-DEBUG-../src/sshmasterconnection.cpp:1977> Creating new channel.
>>>>
>>>>     x2go-DEBUG-../src/sshmasterconnection.cpp:1990> New channel:0x7f5b580102e0
>>>>
>>>>     x2go-DEBUG-../src/sshmasterconnection.cpp:1994> Forwarding parameters: from remote ("localhost":57842) to local ("localhost":35710)
>>>>     x2go-DEBUG-../src/sshmasterconnection.cpp:2028> Temporary session port after config file parse: 57842
>>>>     x2go-DEBUG-../src/sshmasterconnection.cpp:2032> Temporary session host after config file parse: localhost
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:11659> "Searching proxy window: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:13278> "Searching window with title: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:11659> "Searching proxy window: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:13278> "Searching window with title: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:11659> "Searching proxy window: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:13278> "Searching window with title: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     [...]
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:6618> Proxy wrote on stderr: "Info: Aborting the procedure due to signal '15'.\nSession: Session terminated at 'Mon Jan 19 19:46:53 2026'.\n"
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:6475> Deleting Proxy.
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:6520> Waiting for proxy to exit.
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:6544> Checking exit status.
>>>>     x2go-DEBUG-../src/sshprocess.cpp:199> Executing remote command via SshProcess object 3: "x2gocmdexitmessage nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     x2go-DEBUG-../src/sshprocess.cpp:213> this=SshProcess(0x55f9bbed6c50) Running masterCon->addChannelConnection(this, '"475b1d25-5fe0-4e44-abcc-dea30df785f1"', '"bash -l -c 'echo \"X2GODATABEGIN:475b1d25-5fe0-4e44-abcc-dea30df785f1\"; export PATH=\"/usr/local/bin:/usr/bin:/bin\";export TERM=\"dumb\"; x2gocmdexitmessage nass-50-1768844727_stDstartfluxbox_dp24; echo \""');
>>>>     x2go-DEBUG-../src/sshmasterconnection.cpp:1810> Locking SSH channel connection MUTEX.
>>>>     x2go-DEBUG-../src/sshmasterconnection.cpp:2055> "ssh_channel_open_forward failed": "No channel request of this type from server"
>>>>
>>>>     x2go-DEBUG-../src/sshmasterconnection.cpp:2187> "ssh_channel_write failed": "Remote channel is closed"
>>>>
>>>> then it tries to resume
>>>>
>>>>     x2go-DEBUG-../src/sshmasterconnection.cpp:2065> Executing remote: "bash -l -c 'echo \"X2GODATABEGIN:a6aca35a-a72c-4453-96b1-0a2e1b49dfcb\"; export PATH=\"/usr/local/bin:/usr/bin:/bin\";export TERM=\"dumb\"; x2goresume-session nass-50-1768844727_stDstartfluxbox_dp24 800x600 adsl 16m-jpeg-9 us auto 1 both no; echo \"X2GODATAEND:a6aca35a-a72c-4453-96b1-0a2e1b49dfcb\";'"
>>>>
>>>>     x2go-DEBUG-../src/sshmasterconnection.cpp:2071> "ssh_channel_open_session failed": "Socket error: Success"
>>>>
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:11659> "Searching proxy window: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:13278> "Searching window with title: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     x2go-DEBUG-../src/sshprocess.cpp:478> I/O error: "ssh_channel_open_forward failed."" - No channel request of this type from server" (2).
>>>>     x2go-DEBUG-../src/sshprocess.cpp:478> I/O error: "ssh_channel_write failed."" - Remote channel is closed" (2).
>>>>     x2go-DEBUG-../src/sshprocess.cpp:478> I/O error: "ssh_channel_open_session failed."" - Received SSH_MSG_DISCONNECT: 2:oclose packet referred to nonexistent channel 0" (3).
>>>>     x2go-DEBUG-../src/sshprocess.cpp:478> I/O error: "ssh_channel_open_session failed."" - Socket error: Success" (4).
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:11659> "Searching proxy window: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:13278> "Searching window with title: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:11659> "Searching proxy window: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>     x2go-DEBUG-../src/onmainwindow.cpp:13278> "Searching window with title: X2GO-nass-50-1768844727_stDstartfluxbox_dp24"
>>>>
>>>> and afterwards I get the last 2 messages in an endless loop. No desktop window pops up.
>>>>
>>>>
>>>> I am also very confused about the
>>>>
>>>>     "ssh_channel_open_session failed": "Socket error: Success"
>>>>
>>>>
>>>> I have not found any information about how to enable debug output in the server side (only on the client side) and the current messages do not give me a clear view as to what is wrong.
>>>>
>>>> Do you have any idea which way I should look next?
>>>>
>>>> Thank you in advance for your help.
>>>>
>>>>
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