No session on headless server

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  • #3361
    Anamon
    Participant

    I’m trying to run nxserver on a headless RHEL system (no screens attached) in order to access the desktop environment. I’m running into the exact same issues as discussed in this thread: https://www.nomachine.com/forums/topic/nxclient-unable-to-find-session-on-headless-x-server

    The thread ends with a possible but unconfirmed solution, which however doesn’t seem to make any difference in my case.

    The remote access setup works fine if a screen is connected (and then removed) from the server while it is booting up. Any NoMachine client can connect to the machine and interact with the desktop. However, if not screen is present during system boot, the X server isn’t started and no displays are set up for it, so nxclient fails with the message “<No available sessions on this server>” and detailed reason “<The server was unable to make the local display available or access to the local display is disabled.>”

    I tried following both the procedures in https://www.nomachine.com/AR10K00710 and the thread mentioned above, to use Xvfb as an in-memory screen for the X server to run on.

    The command to start Xvfb ends with the message “Initializing built-in extension GLX” (and seemingly hanging there, although it turns out I’m correctly sent back to the shell, just the prompt doesn’t show anymore). Starting gnome-desktop seems to work fine as well, returning me to shell with a background process ID and a lot of Gnome-related child processes running.

    However, none of this makes a difference as far as NoMachine client is concerned. I still get the same messages about no sessions/displays being available on the server machine (even if, as pointed out in the thread, I set a 24-bit display mode for Xvfb). So either something goes wrong while setting up the framebuffer-X, or maybe the nxserver services aren’t correctly invoked (or at all) if the X server is started this way, as opposed to a regular GUI boot.

    Does anyone have any more pointers regarding where I could continue looking for the problem?

    I’m using NoMachine 4.2.21_1 x86_64 on RHEL6 for the server, and NoMachine 4.2.21_1 on Windows 7 x64 as the client, both free versions (no built-in virtual desktop feature).

    #3374
    reza
    Moderator

    Please try the procedure from attachment.
    It was adjusted to RHEL paths and tested on RHEL 6.5.

    Attachments:
    #4120
    cescarpa
    Participant

    I am running the free version of NoMachine 4-2-26 as display server in a opensuse 13.1, and same NoMachine version under OSX for the client side.

    As the starting mail reports, i can access the linux server whenever it has a monitor connected, otherwise i get connected to a black  screen that does not allow me to login or access the server

    I followed the configuration recommendations provided in the article https://www.nomachine.com/AR10K00710 and did not get it to work.

    after executing:

    COOKIE=ps -ef | md5sum | cut -f 1 -d " "
    xauth -f ~/Xvfb-0.auth add :0 MIT-MAGIC-COOKIE-1 $COOKIE
    xauth add :0 MIT-MAGIC-COOKIE-1 $COOKIE
    Xvfb :0 -auth ~/Xvfb-0.auth -screen 0 1024x768x24 &
    DISPLAY=:0 nohup /etc/gdm/Xsession gnome-session &
    
    I can see the Xvfb running: (ps -ax |grep -i x)
    
    but after i run
    DISPLAY=:0 nohup /etc/gdm/Xsession gnome-session &
    it results in an error shown in ~/.xsession-errors-:0
    
    Invalid MIT-MAGIC-COOKIE-1 key/etc/X11/xim.d/es/40-ibus started sucessfully
    Invalid MIT-MAGIC-COOKIE-1 keyxrdb: Resource temporarily unavailable
    xrdb: Can't open display ':0'
    Invalid MIT-MAGIC-COOKIE-1 keyInvalid MIT-MAGIC-COOKIE-1 key
    ** (gnome-session-check-accelerated:13488): WARNING **: Could not open X display
    Invalid MIT-MAGIC-COOKIE-1 keyUnable to init server
    
    (gnome-session-check-accelerated:13488): Gtk-WARNING **: cannot open display: :0
    Invalid MIT-MAGIC-COOKIE-1 key
    #4135
    reza
    Moderator

    We just verified procedure from AR10K00710 on OpenSUSE 13.1 and it works correctly.
    Your logs suggests that there is something wrong with authorization cookie.
    Please execute following commands to assure that cookie is correct and equal in both cases:
    xauth -f ~/Xvfb-0.auth list :0
    xauth list :0

    #4192
    smartin
    Participant

    Hi Anamon,

    I had similar problems on a headless Debian box. The free version of NoMachine 4 only shares the physical screen. In my case Debian booted up with a default VGA configuration (640×480), totally useless for doing any work, but at least a connection. The Workstation license enables virtual desktops, this allows you to connect to the remote box using a screen with the same resolution as your client computer.

    This configuration works OK for me, however personally I would prefer XRANDR support so I can resize the client window size.

    Regards.

    #4219
    dtc42
    Participant

    I also followed the instructions here for NoMachine_4.2.26

    https://www.nomachine.com/AR10K00710

    And was able to get the basic functionality to work on an AWS debian instance. On AWS, typically an “admin” or “ec2-user” is provided with sudo privileges. My goal is to allow NoMachine access to a gnome desktop as the ec2-user.

    Following the KnowledgeBase article as “root”, then I can connect to a desktop using nxplayer — but *only* as the “root” user. (To make this work I also had to modify /usr/NX/etc/server.cfg and change the default values for:  VirtualDesktopAuthorization 0, and PhysicalDesktopAuthorization 0)

    If I try to follow the KnowledgeBase procedure as the “ec2-user” then the nxserver –restart fails.

    > /usr/NX/bin/nxserver –restart
    NX> 500 ERROR: Only a user with administrative privileges
    NX> 500 ERROR: can use option: restart.

    Running nxserver –restart as sudo does work, but then the proper Desktop connections are not displayed in nxplayer.

    Is there any way to provide a headless Desktop connection to a non-root user?

    Thanks!
    -dave

    #4249
    reza
    Moderator

    Please assure that you are following most recent version of article.
    Couple of weeks ago the article was modified to let non root users use it and didn’t include a command for restarting a server anymore. It is no longer needed.

    #4257
    dtc42
    Participant

    Thank you for your quick reply. I did a

    1) clean install of nomachine_4.2.26_1_amd64.deb,
    2) and followed the instructions to start Xvfb on display :0 as a non-root user

    ps -ef shows:

    1002     10252     1  0 18:09 pts/1    00:00:00 Xvfb :0 -auth /home/googlestudent/Xvfb-0.auth -screen 0 1280x1024x24

    and netstat -l shows:

    tcp        0      0 *:4000                  *:*                     LISTEN

    When I try to attach using nxplayer, it actually connects and lets me enter the password for the non-root user, but instead of connecting to the Desktop I get the attached error screen instead (Ooops! Could not start the display server. Error is 5: Input/output error). I will attach the error logs.

    When I try this same sequence as the *root* user, then the final connection to a Desktop is successful, but I would like to do this as a non-root user.

    Thanks!
    -dave

     

     

     

     

    #4280
    Haven
    Contributor

    Hello dtc42,

    We will need nxserver and nxnode logs to investigate further. Please follow the instructions here:

    https://www.nomachine.com/AR07K00677

    Send them to issues[at]nomachine[dot]com

    #4347
    Haven
    Contributor

    Hello dtc42,

    I logs you submitted we found that session because nxserver choose wrong X server to attach to. In user processes we can found two running X servers:

    vnc4           Xvnc4 :1 -desktop localhost:1 (googlestudent) -auth /home/googlestudent/.Xauthority -geometry 1280×1024 -depth 16 -rfbwait 30000 -rfbauth /home/googlestudent/.vnc/passwd -rfbport 5901 -pn -fp /usr/X11R6/lib/X11/fonts/Type1/,/usr/X11R6/lib/X11/fonts/Speedo/,/usr/X11R6/lib/X11/fonts/misc/,/usr/X11R6/lib/X11/fonts/75dpi/,/usr/X11R6/lib/X11/fonts/100dpi/,/usr/share/fonts/X11/misc/,/usr/share/fonts/X11/Type1/,/usr/share/fonts/X11/75dpi/,/usr/share/fonts/X11/100dpi/ -co /etc/X11/rgb

    and

    Xvfb            Xvfb :0 -auth /home/googlestudent/Xvfb-0.auth -screen 0 1280x1024x2

    Please try to disable other X server before connecting to session or uncomment in node.cfg file key:

    #
    # Specify on which physical display the server must connect.
    #
    #DisplayDefault :0

    Then nxserver will always choose X server with display defined in this key.

    • This reply was modified 7 years, 2 months ago by Haven.
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