utmpdump can be useful in cases of corrupted utmp or
wtmp entries. It can dump out utmp/wtmp to an ASCII file, which can then
be edited to remove bogus entries, and reintegrated using:
utmpdump -r < ascii_file > wtmp
But be warned, utmpdump was written for debugging
purposes only.
File formats
Only the binary version of the utmp(5) is
standardised. Textual dumps may become incompatible in future.
The version 2.28 was the last one that printed text output using
ctime(3) timestamp format. Newer dumps use millisecond
precision ISO-8601 timestamp format in UTC-0 timezone. Conversion from
former timestamp format can be made to binary, although attempt to do so
can lead the timestamps to drift amount of timezone offset.