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.\"     @(#)utmp.5	8.2 (Berkeley) 3/17/94
.\" $FreeBSD: src/share/man/man5/utmp.5,v 1.9.2.8 2001/12/17 11:30:15 ru Exp $
.\" $DragonFly: src/share/man/man5/utmp.5,v 1.2 2003/06/17 04:37:00 dillon Exp $
.\"
.Dd November 14, 2001
.Dt UTMP 5
.Os
.Sh NAME
.Nm utmp ,
.Nm wtmp ,
.Nm lastlog
.Nd login records
.Sh SYNOPSIS
.In sys/types.h
.In utmp.h
.Sh DESCRIPTION
The file
.Aq Pa utmp.h
declares the structures used to record information about current
users in the file
.Nm ,
logins and logouts in the file
.Nm wtmp ,
and last logins in the file
.Nm lastlog .
The time stamps of date changes, shutdowns and reboots are also logged in
the
.Nm wtmp
file.
.Bd -literal -offset indent
#define _PATH_UTMP      "/var/run/utmp"
#define _PATH_WTMP      "/var/log/wtmp"
#define _PATH_LASTLOG   "/var/log/lastlog"

#define UT_NAMESIZE     16
#define UT_LINESIZE     8
#define UT_HOSTSIZE     16

struct lastlog {
        time_t  ll_time;		/* When user logged in */
        char    ll_line[UT_LINESIZE];	/* Terminal line name */
        char    ll_host[UT_HOSTSIZE];	/* Host user came from */
};

struct utmp {
        char    ut_line[UT_LINESIZE];	/* Terminal line name */
        char    ut_name[UT_NAMESIZE];	/* User's login name */
        char    ut_host[UT_HOSTSIZE];	/* Host user came from */
        time_t  ut_time;		/* When user logged in */
};
.Ed
.Pp
The
.Nm lastlog
file is a linear array of
.Vt lastlog
structures indexed by a user's
.Tn UID .
The
.Nm
file is a linear array of
.Vt utmp
structures indexed by a terminal line number
(see
.Xr ttyslot 3 ) .
The
.Nm wtmp
file consists of
.Vt utmp
structures and is a binary log file,
that is, grows linearly at its end.
.Pp
Each time a user logs in, the
.Xr login 1
program looks up the user's
.Tn UID
in the file
.Nm lastlog .
If it is found, the timestamp of the last time the user logged
in, the terminal line and the hostname
are written to the standard output (unless the login is
.Em quiet ,
see
.Xr login 1 ) .
The
.Xr login 1
program then records the new login time in the file
.Nm lastlog .
.Pp
After the new
.Vt lastlog
record is written,
.\" the
.\" .Xr libutil 3
.\" routine
the file
.Nm
is opened and the
.Vt utmp
record for the user is inserted.
This record remains there until
the user logs out at which time it is deleted.
The
.Nm
file is used by the programs
.Xr rwho 1 ,
.Xr users 1 ,
.Xr w 1 ,
and
.Xr who 1 .
.Pp
Next, the
.Xr login 1
program opens the file
.Nm wtmp ,
and appends the user's
.Vt utmp
record.
The user's subsequent logout from the terminal
line is marked by a special
.Vt utmp
record with
.Va ut_line
set accordingly,
.Va ut_time
updated, but
.Va ut_name
and
.Va ut_host
both empty
(see
.Xr init 8 ) .
The
.Nm wtmp
file is used by the programs
.Xr last 1
and
.Xr ac 8 .
.Pp
In the event of a date change, a shutdown or reboot, the
following items are logged in the
.Nm wtmp
file.
.Pp
.Bl -tag -width ".Li shutdown" -compact
.It Li reboot
.It Li shutdown
A system reboot or shutdown has been initiated.
The character
.Ql \&~
is placed in the field
.Va ut_line ,
and
.Li reboot
or
.Li shutdown
in the field
.Va ut_name
(see
.Xr shutdown 8
and
.Xr reboot 8 ) .
.Pp
.It Li date
The system time has been manually or automatically updated
(see
.Xr date 1 ) .
The command name
.Li date
is recorded in the field
.Va ut_name .
In the field
.Va ut_line ,
the character
.Ql \&|
indicates the time prior to the change, and the character
.Ql \&{
indicates the new time.
.El
.Sh NOTES
The
.Nm wtmp
file can grow rapidly on busy systems, so daily or weekly rotation
is recommended.
It is maintained by
.Xr newsyslog 8 .
.Pp
If any one of these files does not exist, it is not created by
.Xr login 1 .
They must be created manually.
.Pp
The supplied
.Xr login 3 ,
.Xr logout 3 ,
and
.Xr logwtmp 3
utility functions should be used to perform
the standard actions on the
.Nm
and
.Nm wtmp
files in order to maintain the portability across
systems with different formats of those files.
.Sh FILES
.Bl -tag -width ".Pa /var/log/lastlog" -compact
.It Pa /var/run/utmp
The
.Nm
file.
.It Pa /var/log/wtmp
The
.Nm wtmp
file.
.It Pa /var/log/lastlog
The
.Nm lastlog
file.
.El
.Sh SEE ALSO
.Xr last 1 ,
.Xr login 1 ,
.Xr w 1 ,
.Xr who 1 ,
.Xr login 3 ,
.Xr logout 3 ,
.Xr logwtmp 3 ,
.Xr ttyslot 3 ,
.Xr ac 8 ,
.Xr init 8
.Sh HISTORY
A
.Nm
and
.Nm wtmp
file format appeared in
.At v6 .
The
.Nm lastlog
file format appeared in
.Bx 3.0 .