Hi Harry, Guacamole uses libvncclient, 1.6.0 probably brought along an upgrade of that underlying library, so I think that underlying change is a reasonable hypothesis.
Your logs show "Security Type 2 and Scheme 2", which gives important info on the VNC server. My approach would be to try and connect to the server with a different VNC client than Guacamole as a way to narrow it down. Also understand what VNC server software and version is on the problematic server. Upgrading it might be an easy fix, or switching to a different VNC auth type. On Mon, May 11, 2026 at 8:28 AM Devine, Harry (FAA) via user < [email protected]> wrote: > Does ANYONE have any ideas on this? I have a few dozen users that can no > longer access any of their VNC connections, and they’re all looking to me > to tell them why. And I can’t find anything. I’m really stuck and could > use some help. > > > > Thanks, > > Harry > > > > > > [image: Image] > > Harry Devine > > Secure-OSE System Administrator > > U.S. Department of Transportation > > FAA/AJM-2432 > > (609) 485-4218 (Office) > > (609) 612-7274 (FAA Cell) > > *[email protected] <[email protected]>* > > > > *William J Hughes Technical Center* > > *Building 300 3rd Floor Column L20* > > *Atlantic City NJ 08405* > > > > > > *From:* Devine, Harry (FAA) via user <[email protected]> > *Sent:* Friday, May 8, 2026 10:26 AM > *To:* user <[email protected]> > *Cc:* Devine, Harry (FAA) <[email protected]> > *Subject:* Issue with VNC in 1.6.0 > > > > *CAUTION:* This email originated from outside of the Federal Aviation > Administration (FAA). Do not click on links or open attachments unless you > recognize the sender and know the content is safe. > > > > We upgraded one of our Guacamole servers to 1.6.0 this morning. We’ve > done this to a half-dozen or so previously, so I know it works. But on > this server, the users can now no longer connect to any VNC connections, > and I can’t seem to find what changed. I’ve asked them to verify that the > password for VNC on the connection side is still valid, but they haven’t > checked yet. I thought I’d put an excerpt from the log to see if anyone > has any ideas on where to look for answers. > > > > Thanks, > > Harry > > > > May 8 10:12:33 tfdm-access guacd[78029]: Creating new client for protocol > "vnc" > > May 8 10:12:33 tfdm-access guacd[78029]: Connection ID is > "$40b21c0e-7b73-48b5-88c9-040043ffe7fd" > > May 8 10:12:33 tfdm-access guacd[78486]: Cursor rendering: local > > May 8 10:12:33 tfdm-access guacd[78486]: The libvncclient library does > not support remote resize. > > May 8 10:12:33 tfdm-access guacd[78486]: User > "@e1e7896f-fe81-4967-8fd9-9447460e831a" joined connection > "$40b21c0e-7b73-48b5-88c9-040043ffe7fd" (1 users now present) > > May 8 10:12:33 tfdm-access server[78114]: 10:12:33.494 > [http-nio-8080-exec-1] INFO o.a.g.tunnel.TunnelRequestService - User > "harry.devine" connected to connection "361". > > May 8 10:12:33 tfdm-access server[78114]: 10:12:33.495 > [http-nio-8080-exec-1] INFO o.a.g.t.h.RestrictedGuacamoleHTTPTunnelServlet > - Using HTTP tunnel (not WebSocket). Performance may be sub-optimal. > > May 8 10:12:33 tfdm-access guacd[78486]: VNC server supports protocol > version 3.8 (viewer 3.8) > > May 8 10:12:33 tfdm-access guacd[78486]: We have 1 security types to read > > May 8 10:12:33 tfdm-access guacd[78486]: 0) Received security type 2 > > May 8 10:12:33 tfdm-access guacd[78486]: Selecting security type 2 (0/1 > in the list) > > May 8 10:12:33 tfdm-access guacd[78486]: Selected Security Scheme 2 > > May 8 10:12:33 tfdm-access guacd[78486]: VNC connection failed: > Authentication failure > > May 8 10:12:33 tfdm-access guacd[78486]: Unable to connect to VNC server. > > May 8 10:12:33 tfdm-access guacd[78486]: User > "@e1e7896f-fe81-4967-8fd9-9447460e831a" disconnected (0 users remain) > > May 8 10:12:33 tfdm-access guacd[78486]: Last user of connection > "$40b21c0e-7b73-48b5-88c9-040043ffe7fd" disconnected > > May 8 10:12:33 tfdm-access guacd[78029]: Connection > "$40b21c0e-7b73-48b5-88c9-040043ffe7fd" removed. > > > > > > [image: Image] > > Harry Devine > > Secure-OSE System Administrator > > U.S. Department of Transportation > > FAA/AJM-2432 > > (609) 485-4218 (Office) > > (609) 612-7274 (FAA Cell) > > *[email protected] <[email protected]>* > > > > *William J Hughes Technical Center* > > *Building 300 3rd Floor Column L20* > > *Atlantic City NJ 08405* > > > > >
