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Way back a long time ago, Thompson and Ritchie were sitting opposite one another at the commissary, sipping coffees and discussing their evolving behemoth.

“This behemoth of ours,” said Ken, “is becoming rather popular, wouldn’t you say?” “Yes,” said Dennis. “Every time I want to do a compilation, I have to wait for hours and hours. It’s infuriating.” They both agreed that the load on their system was too great. Both sighed, picked up their mugs, and went back to the workbench. Little did they know that an upper-management type was sitting just within earshot of their conversation.

“We are AT&T Bell Laboratories, aren’t we?” the upper-management type thought to himself. “Well, what is our organization best known for?” The brill-cream in his hair glistened. “Screwing people out of lots of money, of course! If there were some way that we could keep tabs on users and charge them through the nose for their CPU time...”

The accounting utilities were born.

Years later Markus Gothe was a facing the CEO at his work, keep asking him where and how he got the information on other employees payrolls. There was indeed a conflict, Markus denied all the modus operandi on how to get held of such copies or information. Plans was made up to frame him, by interception.

This momement Markus realized the words of Rob Savoye “You cannot buy yourself free from guilt.” He left the room with pride, for making a stand. However, sadly enogh, the CEO never realized that meaning. You cannot buy yourself free from guilt; A new revival had come for the GNU acccounting utilities and so a POSIX-standard.

Seriously though, the accouting utilities can provide a system administrator with useful information about system usage—connections, programs executed, and utilization of system resources.

Information about users—their connect time, location, programs executed, and the like—is automatically recored in files by init and login. Four of them are of interest to us: wtmp, which has records for each login and logout; acct, which records each command that was run; usracct and savacct, which contain summaries of the information in acct by user and command, respectively. Each of the accounting utilities reports or summarizes information stored in these files.


prints statistics about users’ connect time. ac can tell you how long a particular user or group of users were connected to your system, printing totals by day or for all of the entries in the wtmp file.


turns accounting on or off.


lists the commands executed on the system, most recent first, showing the run state of each command. With last, you can search the acct file for a particular user, terminal, or command.


summarizes the information in the acct file into the savacct and usracct file. It also generates reports about commands, giving the number of invocations, cpu time used, average core usage, etc.


display acct and utmp files in a human-readable format.

For more detailed information on any of these programs, check the chapter with the program title.

A Note on File Names and Locations

The wtmp and acct files seem to live in different places and have different names for every variant of u*x that exists. The name wtmp seems to be standard for the login accounting file, but the process accounting file might be acct or pacct on your system. To find the actual locations and names of these files on your system, specify the --help flag to any of the programs in this package and the information will dumped to standard output.

Regardless of the names and locations of files on your system, this manual will refer to the login accounting file as wtmp and the process accounting files as acct, savacct, and usracct.

Support for Multiple Accounting File Formats under Linux

The detailed format of the acct file written by the Linux kernel varies depending on the kernel’s version and configuration: Linux kernels 2.6.7 and earlier write a v0 format acct file which unfortunately cannot store user and group ids (uid/gid) larger than 65535. Kernels 2.6.8 and later write the acct file in v1, v2 or v3 formats. (v3 if BSD_PROCESS_ACCT_V3 is selected in the kernel configuration, otherwise v1 if on the m68k architecture or v2 everywhere else).

Since version 6.4 the GNU accounting utilities on Linux systems are able to read all of the v0, v2 and v3 file formats (v1 is not supported). Thus you do not need to worry about the details given above. You can even read acct files where different records were written by differently configured kernels (you can find out about the format of each entry by using the dump-acct utility). In case you ever need to convert an acct file to a different format, the --raw option of dump-acct does that together with the new --format and --byteswap options that determine format and byte order of the output file.

Multiformat support under Linux is intended to be a temporary solution to aid in switching to the v3 acct file format. So do not expect GNU acct 6.7 to still contain Multiformat support. In a few years time, when everybody uses the v3 format, the ability to read multiple formats at runtime will probably be dropped again from the GNU accounting utilities. This does not, however, affect the ability to adapt to the acct file format at compile time (when ./configure is run). Even GNU acct 6.3.5 (that does not know about multiple file formats) will yield working binary programs when compiled under a (as yet hypothetical) Linux kernel 2.6.62 that is only able to write the v3 format.

History of the Accounting Utilities

I don’t have any idea who originally wrote these utilities. If anybody does, please send some mail to and I’ll add your information here!

Since the first alpha versions of this software in late 1993, many people have contributed to the package. They are (in alphabetical order):

Eric Backus <>

Suggested fixes for HP-UX 9.05 using /bin/cc: configure assumed you were using gcc and tacked on -Wall etc. He also noticed that file_rd.c was doing pointer arithmetic on a void * pointer (non-ANSI).

Christoph Badura <>

Christoph was a BIG HELP in computing statistics, most notably k*sec stuff! He also did Xenix testing and contributed some Makefile fixes and output optimizations.

Michael Calwas <>

Fixed bugs in mktime.c.

Derek Clegg <>

Suggested the simple, elegant fix for *_rd_never_used brain-damage.

Alan Cox <>

Original Linux kernel accounting patches.

Scott Crosby <>

Suggested idea behind --sort-real-time for sa.

Solar Designer <>

Added code for --ahz flag in lastcomm and sa.

Dirk Eddelbuettel <>

Managed bug-fixes & etc. for Debian distribution, as well as the architect of merge of GNU + Debian distributions. A big thanks to Dirk for kicking me back into gear again after a long period of no work on this project.

Jason Grant <>

Identified a buffer-overrun bug in sa.

Kaveh R. Ghazi <>

Tested the package on many systems with compilers other than gcc. Fixed K&R C support.

Susan Kleinmann <>

Contributed excellent man pages!

Alexander Kourakos <>

Inspired the --wide option for last.

Marek Michalkiewicz <>

Suggested the --ip-address flag for last.

David S. Miller <>

Noticed missing GNU-standard makefile rules.

Walter Mueller <>

Noticed install target was missing, and corrected a typo for prefix in

Ian Murdock <>

Tracked down miscellaneous bugs in sa.c under Linux. Added Debian package maintenance files.

Tuomo Pyhala <>

Reported buggy --strict-match flag in lastcomm.

Tim Schmielau <>

Added Linux multiformat support.

Luc I. Suryo <>

Suggested the --user flag for lastcomm.

Pedro A M Vazquez <>

Fixed bugs in sa.c and tested under FreeBSD.

Marco van Wieringen <>

Modified (wrote?) Linux kernel accounting patches.

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