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.\"     @(#)utmp.5	8.2 (Berkeley) 3/17/94
.\"
.Dd May 14, 2003
.Dt UTMP 5
.Os
.Sh NAME
.Nm utmp ,
.Nm wtmp ,
.Nm lastlog
.Nd login records
.Sh SYNOPSIS
.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 utmp ,
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.
.Pp
The
.Nm wtmp
file can grow rapidly on busy systems, and is normally rotated with
.Xr newsyslog 8 .
.Pp
These files must be created manually;
if they do not exist, they are not created automatically.
.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     8
#define UT_LINESIZE     8
#define UT_HOSTSIZE     16

struct lastlog {
        time_t  ll_time;
        char    ll_line[UT_LINESIZE];
        char    ll_host[UT_HOSTSIZE];
};

struct utmp {
        char    ut_line[UT_LINESIZE];
        char    ut_name[UT_NAMESIZE];
        char    ut_host[UT_HOSTSIZE];
        time_t	ut_time;
};
.Ed
.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, providing the login is not set
.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
.Fa lastlog
record is written,
.\" the
.\" .Xr libutil 3
.\" routine
the file
.Nm utmp
is opened and the
.Fa utmp
record for the user inserted.
This record remains there until
the user logs out at which time it is deleted (by clearing
the user and host fields, and updating the timestamp field).
The
.Nm utmp
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
.Fa utmp
record.
When the user logs out, a
.Fa utmp
record with the tty line, an updated time stamp, and cleared user and host
fields is appended to the file by
.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 shutdownxx -compact
.It Li reboot
.It Li shutdown
A system reboot or shutdown has been initiated.
The character
.Ql \&~
is placed in the field
.Fa ut_line ,
and
.Li reboot
or
.Li shutdown
in the field
.Fa ut_name
(see
.Xr shutdown 8
and
.Xr reboot 8 ) .
.Pp
.It Li date
The system time has been manually or automatically updated by
.Xr date 1 .
The command name
.Em date
is recorded in the field
.Fa ut_name .
In the field
.Fa ut_line ,
the character
.Ql \\*(Ba
indicates the time prior to the change, and the character
.Ql \&{
indicates the new time.
.El
.Sh FILES
.Bl -tag -width /var/log/lastlog -compact
.It Pa /var/run/utmp
The
.Nm utmp
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 ac 8 ,
.Xr init 8 ,
.Xr lastlogin 8 ,
.Xr newsyslog 8
.Sh HISTORY
A
.Nm utmp
and
.Nm wtmp
file format appeared in
.At v6 .
The
.Nm lastlog
file format appeared in
.Bx 3.0 .