UTMP(5) BSD File Formats Manual UTMP(5)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.
These files can grow rapidly on busy systems, daily or weekly rotation is
recommended. If any of these files do not exist, it is not created.
These files must be created manually and are normally maintained in
either the script /etc/daily or the script /etc/weekly. (See cron(8).)
#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];
long ut_time;
};
Each time a user logs in, the login 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 quiet, see login(1).) The login pro‐
gram 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. The utmp file is used by the
programs rwho(1), users(1), w(1), and who(1).
Next, the login program opens the file wtmp, and appends the user's utmp
record. The same utmp record, with an updated time stamp is later
appended to the file when the user logs out. (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 charac‐
ter ‘~’ 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.
(See date(1).) The command name date is recorded in the
field ut_name. In the field ut_line, the character ‘|’ indi‐
cates 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 ALSOlast(1), login(1), who(1), 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.
4th Berkeley Distribution June 1, 1994 4th Berkeley Distribution
