sudo: pam_limits(sudo:session): Unknown kernel rlimit 'Max realtime timeout' ignored

PAM stands for Pluggable Authentication Modules. It's basically the Linux (and some other *nix systems) API that apps and system components use for auth.

It's used by both cron and sudo when starting a session for checking session-related limits, as I understand it.

I don't know about the bug itself - you should probably wait a little bit so it gets sorted out, perhaps upstream. It doesn't seem to be critical as both cron and sudo are still working. I take it you're using sid - sometimes Debian unstable just gets bitten by bugs. It's its reason to be.

But if you're interested in just removing the syslog spam you can configure syslog not to log cron and sudo (providing these make up the bulk of the spamming linked to this bug).

First comment out all occurrences of cron in /etc/syslog.conf and add cron.none to your *.* line. In the standard Debian install that would leave it like this:

*.*;auth,authpriv,cron.none  -/var/log/syslog

Which as I understand it means "log everything to /var/log/syslog except ...".

You can alternatively send cron to a separate logfile. See How can I prevent cron from filling up my syslog? for this.

Then:

/etc/init.d/sysklogd restart

For stopping sudo from logging to the syslog add these lines to your /etc/sudoers:

Defaults logfile=/var/log/sudo.log
Defaults !syslog

It should then log to that separate file only.