UTMPDUMP(1) User Commands UTMPDUMP(1)

# [NAME](#NAME)

utmpdump - dump UTMP and WTMP files in raw format

# [SYNOPSIS](#SYNOPSIS)

**utmpdump** \[options] *filename*

# [DESCRIPTION](#DESCRIPTION)

**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.

# [OPTIONS](#OPTIONS)

**-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.

**-h**, **--help**

Display help text and exit.

**-V**, **--version**

Display version and exit.

# [NOTES](#NOTES)

**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](#File_formats)

Only the binary version of the [**utmp**(5)](/man/os/util-linux/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)](/man/os/util-linux/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.

# [BUGS](#BUGS)

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.

# [AUTHORS](#AUTHORS)

Michael Krapp

# [SEE ALSO](#SEE_ALSO)

[**last**(1)](/man/os/util-linux/last.1), [**w**(1)](/man/os/util-linux/w.1), [**who**(1)](/man/os/util-linux/who.1), [**utmp**(5)](/man/os/util-linux/utmp.5)

# [REPORTING BUGS](#REPORTING_BUGS)

For bug reports, use the *issue tracker* <https://github.com/util-linux/util-linux/issues>.

# [AVAILABILITY](#AVAILABILITY)

The **utmpdump** command is part of the util-linux package which can be downloaded from *Linux Kernel Archive* <https://www.kernel.org/pub/linux/utils/util-linux/>.

2026-10-19 util-linux 2.42.4

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Document: utmpdump(1) from util-linux 2.42.4-r1 (Chainguard OS)