NAME
utmp,
wtmp,
lastlog
—
login records
SYNOPSIS
#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.
The
wtmp file can grow rapidly on busy systems, and is
normally rotated with
newsyslog(8).
These files must be created manually; if they do not exist, they are not created
automatically.
#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;
};
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, providing the login is not set
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 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
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. When the user logs out, a
utmp record with the tty line, an updated time stamp,
and cleared user and host fields is appended to the file by
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, and reboot
or
shutdown
in the field
ut_name (see
shutdown(8) and
reboot(8)).
date
- The system time has been manually or automatically updated
by date(1). The command name
date is recorded in the field
ut_name. In the field ut_line,
the character ‘
*(Ba
’ indicates the
time prior to the change, and the character
‘{
’ indicates the new time.
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),
utmpx(5),
ac(8),
init(8),
lastlogin(8),
newsyslog(8)
HISTORY
A
utmp and
wtmp file format appeared in
Version 6 AT&T UNIX. The
lastlog file format appeared in
3.0BSD.