VNC 5 crashes Linux - without even loggin in! (really!)

A few months ago I fully patched SLES 11 SP4 (running kdm) - back when RealVNC 5.1 was shiny and new. I discovered that just attempting to connect to Linux - that is, without even typing any login details - will repeatably crash Linux (not just kdm)! This is indeed very disturbing.

Fortunately, RealVNC 4.1.3 behaved normally with SLES, so I just kept using that. (BTW, RealVNC 5.1 worked normally with OpenSUSE 13.2 - also running kdm.)

Skip forward a few months. I just applied all the latest SLES 11 SP4 (still running kdm) patches and tried the even newer RealVNC 5.3 - the result is the same as before.

Google tells me that nobody else on the planet has had this problem, so I tried switching to gdm. Suddenly, life is beautiful again.

RealVNC 4.3.1 : OpenSUSE/kdm works normally, SLES/kdm works normally, SLES/gdm works normally
RealVNC 5.3 : OpenSUSE/kdm works normally, SLES/kdm crashes, SLES/gdm works normally

Also, logging in on the (virtual) VMWare “console” always works normally.

I will post some /var/log/messages and /var/log/kdm.log details as a follow-up.

Does anyone have any idea what could cause this behavior?

As promised, here the relevant sections of /var/log/kdm.log:

kdmgreet: Fatal IO error: client killed
kdmgreet: Fatal IO error: client killed
kdmgreet: Fatal IO error: client killed
kdmgreet: Fatal IO error: client killed
kdmgreet: cannot connect to X server myhost.mydomain.com:1
kdmgreet: Fatal IO error: client killed
kdmgreet: Fatal IO error: client killed
kdmgreet: Fatal IO error: client killed
kdmgreet: Fatal IO error: client killed
kdmgreet: Fatal IO error: client killed
kdmgreet: Fatal IO error: client killed
kdmgreet: Fatal IO error: client killed

and /var/log/messages:

Dec 22 16:13:51 myhost kdm: myhost.mydomain.com:12[31047]: Abnormal termination of greeter for display myhost.mydomain.com:12, code 1, signal 0
Dec 22 16:13:51 myhost kdm: myhost.mydomain.com:12[31047]: Fatal X server IO error: No such file or directory
Dec 22 16:13:58 myhost kdm_config[31216]: Multiple occurrences of key 'ShowUsers' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:13:58 myhost kdm_config[31216]: Multiple occurrences of key 'UseTheme' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:13:58 myhost kdm: myhost.mydomain.com:13[31221]: Received unknown or unexpected command -2 from greeter
Dec 22 16:13:58 myhost kdm: myhost.mydomain.com:13[31221]: Abnormal termination of greeter for display myhost.mydomain.com:13, code 1, signal 0
Dec 22 16:13:59 myhost kdm_config[31243]: Multiple occurrences of key 'ShowUsers' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:13:59 myhost kdm_config[31243]: Multiple occurrences of key 'UseTheme' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:13:59 myhost kdm: myhost.mydomain.com:14[31248]: Received unknown or unexpected command -2 from greeter
Dec 22 16:13:59 myhost kdm: myhost.mydomain.com:14[31248]: Abnormal termination of greeter for display myhost.mydomain.com:14, code 1, signal 0
Dec 22 16:14:01 myhost kdm_config[31270]: Multiple occurrences of key 'ShowUsers' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:01 myhost kdm_config[31270]: Multiple occurrences of key 'UseTheme' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:01 myhost kdm: myhost.mydomain.com:15[31275]: Received unknown or unexpected command -2 from greeter
Dec 22 16:14:01 myhost kdm: myhost.mydomain.com:15[31275]: Abnormal termination of greeter for display myhost.mydomain.com:15, code 1, signal 0
Dec 22 16:14:04 myhost kdm_config[31297]: Multiple occurrences of key 'ShowUsers' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:04 myhost kdm_config[31297]: Multiple occurrences of key 'UseTheme' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:04 myhost kdm: myhost.mydomain.com:1[31302]: Received unknown or unexpected command -2 from greeter
Dec 22 16:14:04 myhost kdm: myhost.mydomain.com:1[31302]: Abnormal termination of greeter for display myhost.mydomain.com:1, code 1, signal 0
Dec 22 16:14:08 myhost kdm_config[31320]: Multiple occurrences of key 'ShowUsers' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:08 myhost kdm_config[31320]: Multiple occurrences of key 'UseTheme' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:08 myhost kdm: myhost.mydomain.com:16[31325]: Received unknown or unexpected command -2 from greeter
Dec 22 16:14:08 myhost kdm: myhost.mydomain.com:16[31325]: Abnormal termination of greeter for display myhost.mydomain.com:16, code 1, signal 0
Dec 22 16:14:13 myhost kdm_config[31347]: Multiple occurrences of key 'ShowUsers' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:13 myhost kdm_config[31347]: Multiple occurrences of key 'UseTheme' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:13 myhost kdm: myhost.mydomain.com:17[31352]: Received unknown or unexpected command -2 from greeter
Dec 22 16:14:13 myhost kdm: myhost.mydomain.com:17[31352]: Abnormal termination of greeter for display myhost.mydomain.com:17, code 1, signal 0
Dec 22 16:14:19 myhost kdm_config[31376]: Multiple occurrences of key 'ShowUsers' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:19 myhost kdm_config[31376]: Multiple occurrences of key 'UseTheme' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:20 myhost kdm: myhost.mydomain.com:18[31381]: Received unknown or unexpected command -2 from greeter
Dec 22 16:14:20 myhost kdm: myhost.mydomain.com:18[31381]: Abnormal termination of greeter for display myhost.mydomain.com:18, code 1, signal 0
Dec 22 16:14:27 myhost kdm_config[31438]: Multiple occurrences of key 'ShowUsers' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:27 myhost kdm_config[31438]: Multiple occurrences of key 'UseTheme' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:27 myhost kdm: myhost.mydomain.com:19[31443]: Received unknown or unexpected command -2 from greeter
Dec 22 16:14:27 myhost kdm: myhost.mydomain.com:19[31443]: Abnormal termination of greeter for display myhost.mydomain.com:19, code 1, signal 0
Dec 22 16:14:35 myhost kdm_config[31466]: Multiple occurrences of key 'ShowUsers' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:35 myhost kdm_config[31466]: Multiple occurrences of key 'UseTheme' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:35 myhost kdm: myhost.mydomain.com:20[31471]: Received unknown or unexpected command -2 from greeter
Dec 22 16:14:35 myhost kdm: myhost.mydomain.com:20[31471]: Abnormal termination of greeter for display myhost.mydomain.com:20, code 1, signal 0
Dec 22 16:14:44 myhost kdm_config[31493]: Multiple occurrences of key 'ShowUsers' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:44 myhost kdm_config[31493]: Multiple occurrences of key 'UseTheme' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:44 myhost kdm: myhost.mydomain.com:21[31498]: Received unknown or unexpected command -2 from greeter
Dec 22 16:14:44 myhost kdm: myhost.mydomain.com:21[31498]: Abnormal termination of greeter for display myhost.mydomain.com:21, code 1, signal 0
Dec 22 16:14:54 myhost kdm_config[31650]: Multiple occurrences of key 'ShowUsers' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:54 myhost kdm_config[31650]: Multiple occurrences of key 'UseTheme' in section [X-*-Greeter] of /usr/share/kde4/config/kdm/kdmrc
Dec 22 16:14:54 myhost kdm: myhost.mydomain.com:12[31655]: Received unknown or unexpected command -2 from greeter
Dec 22 16:14:54 myhost kdm: myhost.mydomain.com:12[31655]: Abnormal termination of greeter for display myhost.mydomain.com:12, code 1, signal 0

I have read that all these “Multiple occurrences …” messages - despite looking somewhat worrisome - are “normal” - or at least fairly common, and not indicative of a problem.

Any suggestions on where (other than the entire /var/log tree) I might find a more useful error message?