Hi,
it really depends on your name resolution. If you access hostx.my.ipv6.domain and this name resolves to an ipv6 address, this will be used. Also, if you only access the short name hostx and have my.ipv6.domain in the list of domains in /etc/resolv.conf's search line before my.ipv4.domain it will be preferred.
Uli
On Tue, Jan 20, 2026 at 9:48 AM Athanasios Silis <athanasios.silis@gmail.com> wrote:
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 --debugto 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,
nxstartagentis executed fine, andnxproxyalso starts without errors. but then2go-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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