freebsd/share/man/man5/utmp.5

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.\"     @(#)utmp.5	8.2 (Berkeley) 3/17/94
.\" $FreeBSD$
.\"
.Dd March 17, 1994
.Dt UTMP 5
.Os BSD 4
.Sh NAME
.Nm utmp ,
.Nm wtmp ,
.Nm lastlog
.Nd login records
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <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
These files can grow rapidly on busy systems, so daily or weekly rotation
is recommended. 
If any one of these files does not exist, it is not created.
They must be created manually and are maintained by
.Xr newsyslog 8 .
.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;
        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 (unless the login is
.Em quiet ,
see
.Xr login 1 ) .
The
.Nm login
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.
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
program opens the file
.Nm wtmp ,
and appends the user's
.Fa utmp
record.
The same
.Fa utmp
record, with an updated time stamp is later appended
to the file when the user logs out (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 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
(see
.Xr date 1 ) .
The command name
.Xr 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
.Sh HISTORY
A
.Nm utmp
and
.Nm wtmp
file format appeared in
.At v6 .
The
.Nm lastlog
file format appeared in
.Bx 3.0 .