It is a system log file that tracks mostly login events on the 770. It seems to grow larger and larger with use. It will even increase in size every time you put the 770 in its case. I really do not see a need for it. I linked mine to /dev/null which is the "black hole". Any system writes to the file will essentially disappear. It seems to run much better this way. It has been a couple days now configured this way.