Chkwtmp examines the file /var/log/wtmp for entries with no information (containing only null-bytes). If such entries are found the program prints the time window for the original entry. This is done by displaying the timestamps of the wtmp-entry before and after the deleted entry.
To run chkwtmp you need read permission on the file /var/log/wtmp. Normally this file is world-readable and no special privileges are required to run the checker.
This program was designed to run on SunOS 4.x systems only. On other systems the output is undefined...