utmpdump man page

utmpdump — dump UTMP and WTMP files in raw format


utmpdump [options] [filename]


utmpdump is a simple program to dump UTMP and WTMP files in raw format, so they can be examined. utmpdump reads from stdin unless a filename is passed.


-f, --follow
Output appended data as the file grows.
-o, --output file
Write command output to file instead of standard output.
-r, --reverse
Undump, write back edited login information into the utmp or wtmp files.
-V, --version
Display version information and exit.
-h, --help
Display help text and exit.


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

The only 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.


You may not use the -r option, as the format for the utmp/wtmp files strongly depends on the input format. This tool was not written for normal use, but for debugging only.


Michael Krapp

See Also

last(1), w(1), who(1), utmp(5)


The utmpdump command is part of the util-linux package and is available from Linux Kernel Archive.

Referenced By

getutmp(3), utmp(5).

Explore man page connections for utmpdump(1).

util-linux July 2014