utmp(5)

NAME

utmp, wtmp, lastlog - login records

SYNOPSIS

#include <sys/types.h>
#include <utmp.h>

DESCRIPTION

The file #include <utmp.h>
declares the structures used to record information about

current users in
the file utmp, logins and logouts in the file wtmp, and last

logins in
the file lastlog. The time stamps of date changes, shut

downs and reboots
are also logged in the wtmp file.

#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 {

int32_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 lo

gin name */
char ut_host[UT_HOSTSIZE]; /* Host user

came from */
int32_t ut_time; /* When user

logged in */

};

The lastlog file is a linear array of lastlog structures in

dexed by a
user's UID. The utmp file is a linear array of utmp struc

tures indexed
by a terminal line number (see ttyslot(3)). The wtmp file

consists of
utmp structures and is a binary log file, that is, grows

linearly at its
end.

By default, each time a user logs in, the pam_lastlog(8)

program looks up
the user's UID in the file 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. The pam_lastlog(8) program

then records
the new login time in the file lastlog.

After the new lastlog record is written, the file utmp is

opened and the
utmp record for the user is inserted. This record remains

there until
the user logs out at which time it is deleted. The utmp

file is used by
the programs rwho(1), users(1), w(1), and who(1).

Next, the pam_lastlog(8) program opens the file wtmp, and

appends the
user's utmp record. The user's subsequent logout from the

terminal line
is marked by a special utmp record with ut_line set accord

ingly, ut_time
updated, but ut_name and ut_host both empty (see init(8)).

The wtmp file
is used by the programs last(1) and ac(8).

In the event of a date change, a shutdown or reboot, the

following items
are logged in the wtmp file.

reboot
shutdown A system reboot or shutdown has been initiat

ed. The char

acter `~' is placed in the field ut_line, and

reboot or
shutdown in the field ut_name (see shutdown(8)

and
reboot(8)).

date The system time has been manually or automati

cally updated

(see date(1)). The command name date is

recorded in the
field ut_name. In the field ut_line, the

character `|'
indicates the time prior to the change, and

the character
`{' indicates the new time.

NOTES

The wtmp file can grow rapidly on busy systems, so daily or

weekly rotation is recommended. It is maintained by newsyslog(8).

If any one of these files does not exist, it is not created

by
pam_lastlog(8). The files must be created manually.

The supplied login(3), logout(3), and logwtmp(3) utility

functions should
be used to perform the standard actions on the utmp and wtmp

files in
order to maintain the portability across systems with dif

ferent formats
of those files.

FILES

/var/run/utmp The utmp file.
/var/log/wtmp The wtmp file.
/var/log/lastlog The lastlog file.

SEE ALSO

last(1), w(1), who(1), login(3), logout(3), logwtmp(3),

ttyslot(3),
ac(8), init(8), pam_lastlog(8)

HISTORY

A utmp and wtmp file format appeared in Version 6 AT&T UNIX.

The lastlog
file format appeared in 3.0BSD.

BSD November 14, 2001

BSD