veyon-server doesn't start on login-screen

rettich

Hi, everyone,
the current version 4.5.7 of veyon is running on my ubuntu 20.04 client. X11 (not Wayland) runs as the display manager.
A systemctl status veyon.service as root on the Ubuntu client delivers:

root@lz-r99:~# systemctl status veyon.service 
● veyon.service - Veyon Service
     Loaded: loaded (/lib/systemd/system/veyon.service; enabled; vendor preset:>
     Active: active (running) since Sat 2021-08-07 09:59:42 CEST; 13min ago
       Docs: man:veyon-service(1)
   Main PID: 40772 (veyon-service)
      Tasks: 28 (limit: 9495)
     Memory: 64.7M
     CGroup: /system.slice/veyon.service
             ├─40772 /usr/bin/veyon-service
             ├─41151 /usr/bin/veyon-server
             └─41152 /usr/bin/veyon-worker {8e997d84-ebb9-430f-8f72-d45d9821963>

Aug 07 09:59:42 lz-r99 systemd[1]: Started Veyon Service.
Aug 07 09:59:46 lz-r99 veyon-service[40772]: 2021-08-07T09:59:46.632: [WARN] Li>
Aug 07 09:59:49 lz-r99 veyon-service[40772]: 2021-08-07T09:59:49.648: [WARN] QP>

So everything is as it should be.
As soon as the user logs out, the login screen is no longer visible on the teacher's computer. A systemctl status veyon.service as root on the Ubuntu client delivers:

root@lz-r99:~# systemctl status veyon.service 
● veyon.service - Veyon Service
     Loaded: loaded (/lib/systemd/system/veyon.service; enabled; vendor preset:>
     Active: active (running) since Sat 2021-08-07 09:59:42 CEST; 20min ago
       Docs: man:veyon-service(1)
   Main PID: 40772 (veyon-service)
      Tasks: 4 (limit: 9495)
     Memory: 3.9M
     CGroup: /system.slice/veyon.service
             └─40772 /usr/bin/veyon-service

Aug 07 09:59:42 lz-r99 systemd[1]: Started Veyon Service.
Aug 07 09:59:46 lz-r99 veyon-service[40772]: 2021-08-07T09:59:46.632: [WARN] Li>
Aug 07 09:59:49 lz-r99 veyon-service[40772]: 2021-08-07T09:59:49.648: [WARN] QP>

A veyon-server start as root on the Ubuntu client delivers:

root@lz-r99:~# veyon-server start
2021-08-07T10:23:21.701: [ERR] VncServer: no VNC server plugins found!
KLDAP: connection closed!

If a user now logs in, his screen is visible again on the teacher's computer.

Can anyone give me a hint?
Thank you for thinking along.
Greeting,
Mathias

tobydox

Hi @rettich

thank you very much for the detailled information! Did you use a version other than 4.5.7 before, i.e. is this a new behaviour after upgrading to 4.5.7? If so we should try to find the bad change which introduced this behaviour. Starting veyon-server manually is not recommended except for doing so via autostart items inside the user session. When starting as root, it will detect the missing X11 display and thus no VNC server can be used.

rettich

@tobydox
Hello, I've tried both. I upgraded from 4.5.5 to 4.5.7. And I set up veyon on a test system. the effect was the same both times.
Before my update, lightdm was running and now gdm3 is running.
Unfortunately, I can't get to my computer in the next two weeks. Renovation work is taking place in our school. So it will be difficult to try or test something.
Warm greetings,
Mathias

tobydox

@rettich OK let's see if we can fix the problem in the next 2 weeks then. FYI: updated packages (4.5.7-2) for Ubuntu are available in the PPA which revert one change in the 4.5.7 which is suspected to cause the problems. In case you have the chance to test, please report back if everything is OK again after upgrading.

rettich

@tobydox
Hello Tobydox,
I updated veyon to 4.5.7-2. Unfortunately, that made the problem worse:
When an Ubuntu client starts now, I see the screen for about 2 seconds. Then I see this in Veyon-Master:

If I restart the service on the client with Veyon-Configurator, a black screen appears briefly in Veyon-Master. Then you see this again:

One tip would be great.

Regards,
Mathias

hammergil

@rettich
That was my issue as well! Unfortunately there seems to be no answers since it has been weeks since there were any suggestions to fix it.

rettich

@hammergil
Thanks for your answer. So I know that I'm not the only one with this problem.
I set up two computers with ubuntu 20.04 for testing reason. Veyon does not work with gdm3 (with WaylandEnable = false).
Then I installed lightdm. The result was the same. Veyon is not running.
Is there anyone who has Veyon running on an updated ubuntu 20.04?
Funnily enough, Veyon ran before the holidays. Then I updated and Veyon stopped working.

hammergil

@rettich
I gave up and am now using classroomspy found at classroomspy.com. There is a demo to download and try. It cost me $699 for 25 computers and is a 1-time cost which i think is very reasonable.

Not only that, but the developer scheduled a zoom with me to iron out an issue I was having the very same day that I made the purchase.

hammergil

@hammergil
I also asked for a new feature. They put out a new version of the software with my request the very next day.

rettich

@hammergil
I'll wait for ubuntu to be supported again. So far there is no veyon with us.

tobydox

@rettich I'm sorry for the inconveniences. It looks like on the one hand the VNC server crashes, on the other hand the VNC server process can't be terminated in time when switching from the display manager to the user session ("process still running message"). Is there a chance you can downgrade to 4.5.6 by manually installing https://github.com/veyon/veyon/releases/download/v4.5.6/veyon_4.5.6-0-ubuntu-focal_amd64.deb (or even 4.5.5 via https://github.com/veyon/veyon/releases/download/v4.5.5/veyon_4.5.5-0-ubuntu-focal_amd64.deb)?

rettich

@tobydox
Version 4.5.6 works best.
The login screen is visible immediately after the start. When a user logs out, the login screen is no longer visible. I think you can live with that.

However, if you log off a user with veyon-master, the screen remains black. Logging a user off is, I think, an important tool.
Interestingly, the problems do not arise if you use lightdm instead of gdm3.
Greeting,
Mathias

tobydox

Hi @rettich
thank you very much for testing! Today we spent lots of time in debugging and improving the Veyon Service on Linux, especially Ubuntu. If you want you can try the latest build for Ubuntu 20.04 at https://github.com/veyon/veyon/releases/download/v4.5.7/veyon_4.5.7-38-ubuntu-focal_amd64.deb - it should fix multiple issues regarding server start, user logoff and user switch. I'm looking forward to your feedback

rettich

Hi @tobydox
the new version 4.5.7-38 has gotten better. Thank you for your good work.

With veryon-master you can see a lightdm login screen. Unfortunately, veyon-master only shows a black screen for a user logged on to a lightdm computer. You can't even see the username.

If you observe the login screen on a gdm3 computer with veyon-master, you only see a screen that is switched off. As soon as a user is logged in, you can see the screen correctly.

If you log off a user with veyon-master, the screen on the corresponding computer no longer remains black. Another user can now log on to the computer again.

Greeting,
Mathias

tobydox

Hi @rettich
can you please test https://github.com/veyon/veyon/releases/download/v4.5.7/veyon_4.5.7-50-ubuntu-focal_amd64.deb ? It contains further fixes and works flawlessly in our test VMs with Ubuntu/Kubuntu/Lubuntu 20.04. Is your GDM3 configured with WaylandEnabled=false?

rettich

Hi @tobydox,
ubuntu and lightdm work perfectly.

ubuntu and gdm3:
The veyon service does not start automatically when the system is started. When I start veyon-service, the screen of the logged in user is shown in veyon-maser.
If the user logs off again, the login screen in veyon-master can not longer be seen. If the user logs in again, the screen is displayed again in veyon-master.

Is your GDM3 configured with WaylandEnabled=false? Yes.

I hope I can help with my description.
Greeting,
Mathias

tobydox

Hi @rettich

thank you for testing and your feedback! I wonder what's different with your GDM3 or Veyon configuration since here in a fresh Ubuntu 20.04 VM the service starts properly and the login screen can be accessed by Veyon Master. What's the output of systemctl status veyon after booting? Any errors in /tmp/VeyonServ*.log (switch to debug log level before)?

rettich

Hi @tobydox,
it's hard to believe. If I set "debug log level", veyon runs as it should.
I have now set "information, warnings and errors".
At first everything seems to be working again. When I log out I see the login screen in veyon-master (as it should be).
When I log in again I only see a black window in veyon-master.

I am logged in as linuxadmin on lc02. In veyon-master on lc01, however, only a black screen can be seen. The name of the logged on user is not displayed.
systemctl status veyon.service as root returns:

● veyon.service - Veyon Service
     Loaded: loaded (/lib/systemd/system/veyon.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2021-09-14 16:30:06 CEST; 13min ago
       Docs: man:veyon-service(1)
   Main PID: 2732 (veyon-service)
      Tasks: 9 (limit: 9481)
     Memory: 22.3M
     CGroup: /system.slice/veyon.service
             ├─2732 /usr/bin/veyon-service
             └─2807 /usr/bin/veyon-server

Sep 14 16:30:06 lc02 systemd[1]: Started Veyon Service.
Sep 14 16:30:06 lc02 veyon-service[2732]: 2021-09-14T16:30:06.458: [INFO] LinuxServiceCore: Starting server for new session "/org/freedesktop/login1/session/_32" with ID 0 at seat "/org/freedesktop/login1/seat/>
Sep 14 16:30:20 lc02 veyon-service[2732]: 2021-09-14T16:30:20.567: [INFO] LinuxServiceCore: stopping server for removed session "/org/freedesktop/login1/session/_32"
Sep 14 16:30:20 lc02 veyon-service[2732]: 2021-09-14T16:30:20.601: [INFO] LinuxServiceCore: Starting server for new session "/org/freedesktop/login1/session/c1" with ID 0 at seat "/org/freedesktop/login1/seat/s>
Sep 14 16:30:27 lc02 veyon-service[2732]: 2021-09-14T16:30:27.661: [INFO] LinuxServiceCore: stopping server for removed session "/org/freedesktop/login1/session/c1"
Sep 14 16:30:31 lc02 veyon-service[2732]: 2021-09-14T16:30:31.709: [WARN] LinuxServerProcess: server for session "/org/freedesktop/login1/session/c1" still running - killing now
Sep 14 16:30:34 lc02 veyon-service[2732]: 2021-09-14T16:30:34.742: [INFO] LinuxServiceCore: Starting server for new session "/org/freedesktop/login1/session/_35" with ID 0 at seat "/org/freedesktop/login1/seat/>
Sep 14 16:30:38 lc02 veyon-service[2732]: 2021-09-14T16:30:38.858: [WARN] LinuxServerProcess: server for session "/org/freedesktop/login1/session/c1" still running - killing now

And here are the contents of the log files:

root@lc02:/tmp# cat Veyon
VeyonFeatureWorker-8e997d84-ebb9-430f-8f72-d45d9821963d.log  VeyonServiceDataManager                                      
VeyonServer.log                                              VeyonService.log                                             
root@lc02:/tmp# cat VeyonService.log 
2021-09-14T16:30:06.458: [INFO] LinuxServiceCore: Starting server for new session "/org/freedesktop/login1/session/_32" with ID 0 at seat "/org/freedesktop/login1/seat/seat0"
2021-09-14T16:30:20.567: [INFO] LinuxServiceCore: stopping server for removed session "/org/freedesktop/login1/session/_32"
2021-09-14T16:30:20.601: [INFO] LinuxServiceCore: Starting server for new session "/org/freedesktop/login1/session/c1" with ID 0 at seat "/org/freedesktop/login1/seat/seat0"
2021-09-14T16:30:27.661: [INFO] LinuxServiceCore: stopping server for removed session "/org/freedesktop/login1/session/c1"
2021-09-14T16:30:31.709: [WARN] LinuxServerProcess: server for session "/org/freedesktop/login1/session/c1" still running - killing now
2021-09-14T16:30:34.742: [INFO] LinuxServiceCore: Starting server for new session "/org/freedesktop/login1/session/_35" with ID 0 at seat "/org/freedesktop/login1/seat/seat0"
2021-09-14T16:30:38.858: [WARN] LinuxServerProcess: server for session "/org/freedesktop/login1/session/c1" still running - killing now

root@lc02:/tmp# cat Veyon
VeyonFeatureWorker-8e997d84-ebb9-430f-8f72-d45d9821963d.log  VeyonServiceDataManager                                      
VeyonServer.log                                              VeyonService.log                                             
root@lc02:/tmp# cat VeyonServer.log 
2021-09-14T16:30:06.758: [INFO] ComputerControlServer: Access control successful for "::ffff:192.168.0.42" "linuxadmin"
2021-09-14T16:30:20.702: [WARN] VariantStream: none or invalid data read
2021-09-14T16:30:20.702: [ERR] PersistentLogonCredentials: Empty data
2021-09-14T16:30:21.361: [INFO] ComputerControlServer: Access control successful for "::ffff:192.168.0.42" "linuxadmin"
2021-09-14T16:30:34.811: [ERR] FeatureWorkerManager: can't listen on localhost!
2021-09-14T16:30:34.823: [WARN] VncProxyServer: could not listen on port 11100 "Die angegebene Adresse ist bereits in Gebrauch"
2021-09-14T16:30:34.823: [ERR] main: Failed to start server

Once again, thank you very much for your help.
Greeting,
Mathias

tobydox

You identified the actual issue here: when killing server instances, Veyon Service kills the Veyon Server process and all children process recursively. However due to a missing code line, the base process itself was not killed. In debug mode, veyon-server is run as a child of catchsegv so it's killed properly. I commited a fix and uploaded a new build: https://github.com/veyon/veyon/releases/download/v4.5.7/veyon_4.5.7-56-ubuntu-focal_amd64.deb

rettich

Hi @tobydox ,
it's much better now.
When the Linux client starts, its login screen is displayed correctly in veyon-master.
If a user then logs in, his screen is also displayed correctly in Veyon-master.
If the user logs off again immediately, the login screen is no longer displayed in veyon-master.

If a user logs in again, his screen is displayed correctly again. If this user logs off after a few minutes, the login screen is displayed correctly.

Well, even if the login screen is not displayed, you can work well with this version of veyon.

Thanks very much

Mathias

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veyon-server doesn't start on login-screen