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[thirdparty/man-pages.git] / man5 / utmp.5

.\" Copyright (c) 1993 Michael Haardt (michael@cantor.informatik.rwth-aachen.de),
.\" Fri Apr  2 11:32:09 MET DST 1993
.\"
.\" SPDX-License-Identifier: GPL-2.0-or-later
.\"
.\" Modified 1993-07-25 by Rik Faith (faith@cs.unc.edu)
.\" Modified 1995-02-26 by Michael Haardt
.\" Modified 1996-07-20 by Michael Haardt
.\" Modified 1997-07-02 by Nicolás Lichtmaier <nick@debian.org>
.\" Modified 2004-10-31 by aeb, following Gwenole Beauchesne
.TH utmp 5 (date) "Linux man-pages (unreleased)"
.SH NAME
utmp, wtmp \- login records
.SH SYNOPSIS
.nf
.B #include <utmp.h>
.fi
.SH DESCRIPTION
The
.I utmp
file allows one to discover information about who is currently using the
system.
There may be more users currently using the system, because not
all programs use utmp logging.
.PP
.B Warning:
.I utmp
must not be writable by the user class "other",
because many system programs (foolishly)
depend on its integrity.
You risk faked system logfiles and
modifications of system files if you leave
.I utmp
writable to any user other than the owner and group owner of the file.
.PP
The file is a sequence of
.I utmp
structures,
declared as follows in
.I <utmp.h>
(note that this is only one of several definitions
around; details depend on the version of libc):
.PP
.in +4n
.EX
/* Values for ut_type field, below */

#define EMPTY         0 /* Record does not contain valid info
                           (formerly known as UT_UNKNOWN on Linux) */
#define RUN_LVL       1 /* Change in system run\-level (see
                           \fBinit\fP(1)) */