Forum OpenACS Q&A: Response to servername-error.log
First, stop the server, move the logfile to a different filename, then restart the server. This will cause new log entries to go to a newly created error.log, and allow you to work on the other file without doing something that might make AOLserver get confused.
I would suggest that you use the "split" command to split the error.log file into more manageable chunks. Then you can use less, vi, emacs, or whatever you prefer to look at the chunks. The split man page will have more information for you on how to use it.
If this doesn't work for you, then the answer is to use a combination of "tail -f error.log" to see any new entries that are added, tail -n to display a certain number of lines at the end of the file, and grep.