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
ut_line
,
and
reboot
or
shutdown
in the field
ut_name
(see
shutdown(8)
and
reboot(8)).
date
ut_name
.
In the field
ut_line
,
the character
`'
indicates the time prior to the change, and the character
`{'
indicates the new time.
/var/run/utmp
/var/log/wtmp
/var/log/lastlog
AT&T UNIX
.
The
lastlog
file format appeared in
3.0BSD.