I'm not a KDE user, but a search came up with this:
KDM accepts two command line options related to logging:
-debug <n> (druuna: not of interest for this thread, text removed)
<file> is the file to log various messages to. The default log file is
/var/log/kdm.log. For internal reasons there is no option in kdmrc to
permanently specify the log file location. If you redirect KDM's
standard error output to a file, KDM will log there.
If KDM is configured to use syslog (and it _very_ probably is on any
modern system), all internally generated messages are logged to the
"daemon" facility. The log usually can be found in /var/log/debug.log
and /var/log/daemon.log; make sure that daemon.* is logged (look at
All this comes from: developer.kde.org
(halfway down the page, the "It doesn't work!!" section).
BTW: Wouldn't it be a better idea to solve the issues (why is kdm sending so many log messages, can you solve this).
Hope this helps.