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Alwin Lubbers avatar Ubuntu

Running multiple simultaneous VNC sessions

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Alwin Lubbers

I'm working on a project for a client that wants to access some Windows-apps via my website using noVNC, that gave me an idea for setting up a server with multiple users. I've installed TigerVNC-server on my CentOS 7 VPS, which works well when one user is connected, but when the second user connects, he/she will only get a black screen as it seems like gnome won't start for the second user.

If i, for example run the vncservice@:1 it all works fine and the user will be logged in no problem but when vncservice@:2 starts, it won't start gnome and he/she will get a black screen with only a cursor. When vncservice@:2 starts first, that user will be launched in to gnome but vncservice@:1 won't see their desktop etc. etc.

This is what my setup looks like:

[User 1 and 2 ~/.vnc/xstartup]
#!/bin/sh

unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS
/etc/X11/xinit/xinitrc
# Assume either Gnome or KDE will be started by default when installed
# We want to kill the session automatically in this case when user logs out. In case you modify
# /etc/X11/xinit/Xclients or ~/.Xclients yourself to achieve a different result, then you should
# be responsible to modify below code to avoid that your session will be automatically killed

sleep 60

if [ -e /usr/bin/gnome-session -o -e /usr/bin/startkde ]; then
    vncserver -kill $DISPLAY
    killall -u $USER
fi

[/etc/X11/xinit/xinitrc]

#!/bin/sh

# Mandatorily source xinitrc-common, which is common code shared between the
# Xsession and xinitrc scripts which has been factored out to avoid duplication
. /etc/X11/xinit/xinitrc-common

# The user may have their own clients they want to run.  If they don't,
# fall back to system defaults.
if [ -f $HOME/.Xclients ]; then
    exec $CK_XINIT_SESSION $SSH_AGENT $HOME/.Xclients || \
    exec $CK_XINIT_SESSION $SSH_AGENT $HOME/.Xclients
elif [ -f /etc/X11/xinit/Xclients ]; then
    exec $CK_XINIT_SESSION $SSH_AGENT /etc/X11/xinit/Xclients || \
    exec $CK_XINIT_SESSION $SSH_AGENT /etc/X11/xinit/Xclients
else
    # Failsafe settings.  Although we should never get here
    # (we provide fallbacks in Xclients as well) it can't hurt.
    [ -x /usr/bin/xsetroot ] && /usr/bin/xsetroot -solid '#222E45'
    [ -x /usr/bin/xclock ] && /usr/bin/xclock -geometry 100x100-5+5 &
    [ -x /usr/bin/xterm ] && xterm -geometry 80x50-50+150 &
    [ -x /usr/bin/twm ] && /usr/bin/twm
fi

[vncserver@:1 and vncserver@:2, is replace with the actual username]

[Unit]
Description=Remote desktop service (VNC)
After=syslog.target network.target

[Service]
Type=forking
User=<USERNAME>
Group=<USERNAME>

ExecStartPre=-/usr/bin/vncserver -kill %i
ExecStart=/usr/bin/vncserver %i
PIDFile=/home/<USERNAME>/.vnc/%H%i.pid
ExecStop=-/usr/bin/vncserver -kill %i


[Install]
WantedBy=multi-user.target

[Second user VNC log]

[root@.... ~]# systemctl status vncserver@:5
● vncserver@:5.service - Remote desktop service (VNC)
   Loaded: loaded (/etc/systemd/system/vncserver@:5.service; disabled; vendor preset: disabled)
   Active: active (running) since za 2021-07-24 19:04:54 CEST; 59s ago
  Process: 25990 ExecStart=/usr/bin/vncserver %i (code=exited, status=0/SUCCESS)
  Process: 25981 ExecStartPre=/usr/bin/vncserver -kill %i (code=exited, status=2)
 Main PID: 25997 (Xvnc)
   CGroup: /system.slice/system-vncserver.slice/vncserver@:5.service
           ├─25997 /usr/bin/Xvnc :5 -auth /home/AHtYezzDXegQScyu/.Xauthority -desktop <HOSTNAME>:5 (AHtYezzDXegQScyu) -fp catalogue:/etc/X11/fontpath.d -geometry 1024x768 -pn -rfbauth /home/AHtYezzDXegQScyu/.vnc/passwd -rfbport 5905 -rfbwait 30000
           ├─26006 /bin/sh /home/AHtYezzDXegQScyu/.vnc/xstartup
           ├─26018 dbus-launch --sh-syntax --exit-with-session
           ├─26019 /usr/bin/dbus-daemon --fork --print-pid 5 --print-address 7 --session
           ├─26053 /usr/libexec/imsettings-daemon
           ├─26057 /usr/libexec/gvfsd
           ├─26062 /usr/libexec/gvfsd-fuse /home/AHtYezzDXegQScyu/.gvfs -f -o big_writes
           ├─26126 /usr/libexec/at-spi-bus-launcher
           ├─26131 /usr/bin/dbus-daemon --config-file=/usr/share/defaults/at-spi2/accessibility.conf --nofork --print-address 3
           ├─26135 /usr/libexec/at-spi2-registryd --use-gnome-session
           ├─26158 /usr/bin/gnome-keyring-daemon --start --components=ssh
           ├─26241 /usr/libexec/xdg-permission-store
           ├─26246 /usr/libexec/gnome-shell-calendar-server
           ├─26251 /usr/libexec/evolution-source-registry
           ├─26258 /usr/libexec/goa-daemon
           ├─26269 /usr/libexec/goa-identity-service
           ├─26275 /usr/libexec/mission-control-5
           ├─26286 /usr/libexec/gvfs-udisks2-volume-monitor
           ├─26293 /usr/libexec/gvfs-mtp-volume-monitor
           ├─26299 /usr/libexec/gvfs-goa-volume-monitor
           ├─26305 /usr/libexec/gvfs-gphoto2-volume-monitor
           ├─26310 /usr/bin/dbus-daemon --fork --print-pid 5 --print-address 7 --session
           ├─26311 /usr/libexec/gvfs-afc-volume-monitor
           ├─26411 /usr/libexec/gsd-print-notifications
           ├─26413 /usr/libexec/gsd-rfkill
           ├─26418 /usr/libexec/gsd-screensaver-proxy
           ├─26454 sleep 60
           └─26458 /usr/libexec/evolution-calendar-factory

jul 24 19:05:22 <HOSTNAME> gnome-session-binary[26007]: WARNING: Failed to start app: Unable to start application: Failed to fork (Resource temporarily unavailable)
jul 24 19:05:22 <HOSTNAME> gsd-print-notif[26411]: Could not execute system-config-printer-udev handler: Failed to fork (Resource temporarily unavailable)
jul 24 19:05:22 <HOSTNAME> gnome-session-binary[26007]: WARNING: Application 'org.gnome.SettingsDaemon.Power.desktop' killed by signal 5
jul 24 19:05:22 <HOSTNAME> gnome-session[26007]: gnome-session-binary[26007]: WARNING: Application 'org.gnome.SettingsDaemon.Power.desktop' killed by signal 5
jul 24 19:05:22 <HOSTNAME> gnome-session-binary[26007]: GLib-WARNING: GError set over the top of a previous GError or uninitialized memory.
                                                                       This indicates a bug in someone's code. You must ensure an error is NULL before it's set.
                                                                       The overwriting error message was: Unable to start application: Failed to fork (Resource temporarily unavailable)...
jul 24 19:05:22 <HOSTNAME> gnome-session[26007]: gnome-session-binary[26007]: GLib-WARNING: GError set over the top of a previous GError or uninitialized memory.
jul 24 19:05:22 <HOSTNAME> gnome-session[26007]: This indicates a bug in someone's code. You must ensure an error is NULL before it's set.
jul 24 19:05:22 <HOSTNAME> gnome-session[26007]: The overwriting error message was: Unable to start application: Failed to fork (Resource temporarily unavailable)
jul 24 19:05:22 <HOSTNAME> evolution-calen[26465]: creating thread 'gdbus': Error creating thread: Resource temporarily unavailable
jul 24 19:05:47 <HOSTNAME> gnome-shell-cal[26246]: Could not load source 'birthdays': Timeout was reached

[/etc/X11/xinit/Xclients]

#!/bin/bash

GSESSION="$(type -p gnome-session)"
STARTKDE="$(type -p startkde)"

# check to see if the user has a preferred desktop
PREFERRED=
if [ -f /etc/sysconfig/desktop ]; then
    . /etc/sysconfig/desktop
    if [ "$DESKTOP" = "GNOME" ]; then
        PREFERRED="$GSESSION"
    elif [ "$DESKTOP" = "KDE" ]; then
        PREFERRED="$STARTKDE"
    fi
fi

if [ -n "$PREFERRED" ]; then
    exec "$PREFERRED"
fi

# now if we can reach here, either no desktop file was present,
# or the desktop requested is not installed.

if [ -n "$GSESSION" -a -f /usr/share/xsessions/gnome.desktop ]; then
    # by default, we run GNOME.
    exec "$GSESSION" --session=gnome
elif [ -n "$STARTKDE" ]; then
    # if GNOME isn't installed, try KDE.
    exec "$STARTKDE"
fi

# We should also support /etc/X11/xinit/Xclients.d scripts
XCLIENTS_D=/etc/X11/xinit/Xclients.d
if [ "$#" -eq 1 ] && [ -x "$XCLIENTS_D/Xclients.$1.sh" ]; then
    exec -l $SHELL -c "$SSH_AGENT $XCLIENTS_D/Xclients.$1.sh"
fi

# Failsafe.

# these files are left sitting around by TheNextLevel.
rm -f $HOME/Xrootenv.0

# Argh! Nothing good is installed. Fall back to twm
{
    # gosh, neither fvwm95 nor fvwm2 is available;
    # fall back to failsafe settings
    [ -x /usr/bin/xsetroot ] && /usr/bin/xsetroot -solid '#222E45'

    if [ -x /usr/bin/xclock ] ; then
        /usr/bin/xclock -geometry 100x100-5+5 &
    fi
    if [ -x /usr/bin/xterm ] ; then
        /usr/bin/xterm -geometry 80x50-50+150 &
    fi
    if [ -x /usr/bin/firefox -a -f /usr/share/doc/HTML/index.html ]; then
        /usr/bin/firefox /usr/share/doc/HTML/index.html &
    fi
    if [ -x /usr/bin/twm ] ; then
        exec /usr/bin/twm
    fi
}

The stupid thing is, after trying to start the second vncserver about 50 times, it usually works one time, when i stop and start the service again it won't show anything again, except for a mouse cursor.

There is plenty of free memory left (about 5 gigs), there also is plenty of storage space left (about 100 gigs). When i edit my ~/.vnc/xstartup file to include only a file manager, it works fine everytime, trying to run a session for multiple users seems to be the problem.

Thanks for reading trough all of this, i've already lost countless hours trying to debug this without any (major) improvements.

UPDATE 1: After many hours of more tinkering, i still didn't get gnome working. Desperate times call for desperate measures so i just ended up installing Xfce and made it prettier with a nice theme and a icon pack. It just worked after i installed it. I removed all gnome references from the xstartup files and added startxfce4.

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