Switching users is definitely not supported, because the TurboVNC Server
(Xvnc) process is owned by the user that started the TurboVNC session.
If you are using GNOME 3, then you are probably observing a symptom of
this issue:
https://github.com/TurboVNC/turbovnc/issues/238
GNOME 3 is just generally not very multi-session-friendly. You can
successfully use GNOME 3 with multiple simultaneous TurboVNC sessions
under the same user account, but per above, there are some known issues
with screen locking. Since most multi-user deployments of the TurboVNC
Server are on headless systems without local login capabilities,
disabling screen locking is a viable workaround for those systems. In
your case, you might want to consider a different window manager, such
as MATE or Xfce, that is more multi-session-friendly. You can use the
$wm variable in /etc/turbovncserver.conf or ~/.vnc/turbovncserver.conf
to specify that the TurboVNC Server should use a different window
manager than the local session, which would allow you to continue using
GNOME 3 with the local session.
As an aside, to the best of my (admittedly limited) understanding, this
relates to two resources: the D-Bus session and the XDG session. The
TurboVNC Server creates a unique D-Bus session for every TurboVNC
session, but all TurboVNC sessions running under the same user account
will share the same XDG session. That seems to be the root of the
screen locking issues. With TigerVNC, as an example, all VNC sessions
under the same user account share both the D-Bus session and XDG
session, so you can't start multiple simultaneous GNOME 3 instances
under the same user account at all. (Because all VNC sessions share the
same D-Bus session, TigerVNC also doesn't allow multiple simultaneous
instances of other window managers, such as MATE, that would otherwise
work fine.) We allow the same WM to be used with multiple simultaneous
VNC sessions under the same user account, but there are some caveats
when using GNOME 3.
DRC
On 7/26/22 4:24 AM, Felix Natter wrote:
hello TurboVNC community,
I am using TurboVNC 3.0 on client and server. On machine A,
I start a VNC server:
/opt/TurboVNC/bin/vncserver :1
Then I lock the session on A and go to machine B
(in this case they are in the same network, but in reality B could be
remote)
On machine B I connect to A:1 using:
/opt/TurboVNC/bin/vncviewer -Toolbar=0 -Shared=0 -MenuKey=F2 \
-Encoding=Tight -JPEG=1 -Quality=70 -CompressLevel=7 -Subsampling=4x \
A:1
I lock virtual session A:1 from B, and when I login again,
the physical session A:0 is also unlocked.
This is obviously a security problem.
If I log out cleanly on A (instead of locking the screen),
and redo the test, the problem is not reproducible any more
until I restart the VNC server on A.
~/.vnc/A:1.log looked unsuspicious (shall I post parts of it here?).
Also, if I do a switch user on a localhost:1 vncviewer session,
it triggers a switch user on :0. But I guess this is not supported.
Both machines are using Scientific Linux 7.9 ("Redhat7").
Many Thanks in Advance and Best Regards,
Felix
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