Screenlocking fails with SLE 15 SP4

[Frank Steiner]

Hi,

after upgrading from SuSE Linux Enterprise Desktop SP3 to SP4 we realized that NoMachine would not always lock the screen when nxplayer disconnects. We always connect to the physical screen.

1) When it first happened with ctwm and with xfce we restarted nxserver (without restarting the desktop session) after which locking an disconnection worked again. A while later I managed to collect a log where disconnecting from xfce didn’t lock the screen (with xlock), but the subsequent disconnects did, although we did not restart neither nxserver nor the desktop session.

2) We use kdm or sddm as login manager as gdm has some problems. With 15 SP3 nxserver would lock the screen also when using gnome as desktop (from kdm/ssdm). As the gdm screenlocked isn’t available with kdm/sddm, nxserver used xscreensaver if the user had started it or xlock otherwise. With 15 SP4, gnome desktops are never locked by nxserver when started from kdm or sddm.

This might be because the dbus name for the locking message has changed. With dbus-monitor I can see that the signals for locking the screen are still sent by nxserver, but while on SP3 (gnome-session-3.34) the message looks like
    mc    1666360979.211103    2    :1.135    org.freedesktop.ScreenSaver    /ScreenSaver    org.freedesktop.ScreenSaver    Lock
there are 3 messages in SP4:
mc    1666361095.639973    37    :1.63    org.gnome.Shell.ScreenShield    /org/gnome/ScreenSaver    org.gnome.ScreenSaver    Lock
mc    1666361095.690794    2    :1.103    org.freedesktop.ScreenSaver    /ScreenSaver    org.freedesktop.ScreenSaver    Lock
mc    1666361095.944046    42    :1.63    org.gnome.Shell.ScreenShield    /org/gnome/ScreenSaver    org.gnome.ScreenSaver    Lock
I write a little python proxy and saw that only this variant would work:
def __init__(self):
session_bus = dbus.SessionBus()
bus_name=dbus.service.BusName("org.gnome.Shell.ScreenShield",bus=session_bus)
dbus.service.Object.__init__(self,bus_name, '/org/gnome/ScreenSaver')
@dbus.service.method("org.gnome.ScreenSaver")
def Lock(self):
os.system( "/usr/bin/touch /tmp/t3" )

I.e. using org.gnome.Shell.ScreenShield as service.BusName but /org/gnome/ScreenSaver for the Object and method. The ScreenShield name is new in Gnome 41.

So maybe NoMachine 8 is doing sth. wrong with sending the correct bus message? But it seems it doesn’t realize it because I cannot see any message (as  has been in other issues with screen locking) that dbus failed and therefore a fallback to xlock would be used. NoMachine seems to thins that dbus locking went fine although it has no effect.

I send the logs for both cases if you want.

cu,

Frank

[Britgirl]

Hi, thanks for the information, we are investigating and will come back to you.

[og00r]

A while later I managed to collect a log where disconnecting from xfce didn’t lock the screen (with xlock),

Any chance for those collected logs? If possible I prefer logs from /home//.nx/
where is physical desktop owner when problem happen.

[Frank Steiner]

Not sure if the debugging was set accordingly for the logs in user home, but I can send them together with the global nxserver.log so that you can filter the matching logs from the users home. Where do I send them?

[Britgirl]

Please send to forum[at]nomachine[dot]com making sure to use the topic’s title as the subject of your email. Thanks!

[Frank Steiner]

I will send them. In the meantime I detected another bug with SLE 15 SP4 that I can reliably reproduce: when using gnome as desktop (we don’t used gdm but kdm or sddm for login, I’m not sure if it’s related to that or not) it will start in a somewhat strange mode. It shows the “Activities” button and a search field and some icons at the bottom. But the background image is smaller and only when you click on it, it will maximize and show the usual desktop icons. I thinks that the workspace you must activate by this first click in gnome-session-41.3.

Anyway, in this initial state where the desktop is not yet clicked, NX will not even try to lock the screen when disconnecting. I tailed ~/.nx/nxserver.log and there appears no line at all when disconnecting, no matter how often I re- and disconnect. But as soon as I clock the background image and desktop appears and I disconnect, I will see messages about org.gnome.ScreenSaver and also my test script I quoted above will receive a signal again.

Do you want logs for that problem, too?

[Britgirl]

We have opened a Trouble Report which can be monitored using the following link:

https://kb.nomachine.com/TR02T10471

We reproduced the same issue on Debian and also with the following envs:

sddm + gnome 43
gdm 43 + xfce4

On the other hand gdm + gnome 43 did not show the error.

[Author]

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