Computers have been taught to distrust each other and will reject attempted connections most of the time. Nowadays, most computers and firewalls are utterly rude about it: it would be like asking someone to dance and having them ignore you as though you were invisible and inaudible. (Tony Lawrence)
Syslog can be run with a -m " option that just writes "- MARK
--" at whatever intervals you specify. The purpose is to provide
reassurance that syslogd is listening and doing its job even if it
has nothing else to do right now.
I've had people worried by their seeing MARK in logs and not
knowing why it was there, but until this thread I'd never seen
anyone wondering why it WASN'T there. The reason is that syslogd
doesn't bother to write a mark if something else cause it to write
a log entry during the interval you specified. After all, the point
of -m is to know that syslogd is alive and working, so why write a
special mark if it just did real work? That's apparently the
attitude of whoever wrote it, and it isn't entirely unreasonable,
though as someone mentioned in this thread, it probably should be
noted in the documentation.
So - if you are seeing "MARK, that's normal. Most systems are
set up to do that. It lets you know that syslog has been doing its
job, it isn't dead, there's just nothing to do right now. If you are NOT
seeing it, but are seeing regular activity from other sources, that's
normal too - don't worry about it.
Other Syslog issues
Another syslog issue that comes up now and then is syslog NOT
writing to a log after you've told it to do so in
/etc/syslog.conf. That's usually because you forgot to create the file; "man syslog" specifically says "For security reasons, syslogd will not append to log files that do not
exist; therefore, they must be created manually before running syslogd.".
"ttloop: peer died" could mean someone is scanning for open ports.
Entries complaining about passwords mean someone has mistyped a
password or is trying to guess one. Back in the days of dumb terminals,
you'd see this when someone left a book lying on a keyboard.