[PLUG] Explanation for message log entry

[Rich Shepard]

   When I view /var/log/messages I see an entry every half-hour when I'm
logged into the system:

Jun 10 05:47:56 salmo -- MARK --
Jun 10 06:07:56 salmo -- MARK --
Jun 10 06:27:56 salmo -- MARK --
Jun 10 06:47:56 salmo -- MARK --
Jun 10 07:07:56 salmo -- MARK --
Jun 10 07:27:56 salmo -- MARK --
Jun 10 07:47:56 salmo -- MARK --
(so far today)

   I'm curious where this originates and what it means. It's obviously benign
and seems harmless and I'm curious what generates this entry and why. My web
search foo was not up to the task of finding an explanation.

Rich