NAME
utmp
, wtmp
,
lastlog
—
login records
SYNOPSIS
#include
<sys/types.h>
#include <utmp.h>
DESCRIPTION
The file<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, shutdowns
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 { 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 */ };
The lastlog
file is a linear array of
lastlog structures indexed by a user's UID. The
utmp
file is a linear array of
utmp structures 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.
Each time a user logs in, the
login(1) 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 (unless the login is
quiet, see
login(1)). The
login(1) 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
login(1) 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
accordingly, 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 initiated. The character
‘
~
’ is placed in the field ut_line, andreboot
orshutdown
in the field ut_name (see shutdown(8) and reboot(8)). date
- The system time has been manually or automatically 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 login(1). They 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 different
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), login(1), w(1), who(1), login(3), logout(3), logwtmp(3), ttyslot(3), ac(8), init(8)
HISTORY
A utmp
and wtmp
file format appeared in Version 6 AT&T
UNIX. The lastlog
file format appeared in
3.0BSD.