UTMP(5) File Formats Manual UTMP(5)NAME
utmp, wtmp - logged in users, login and logout history
SYNOPSIS
#include <sys/types.h>
#include <utmp.h>
DESCRIPTION
The files /etc/utmp and /usr/adm/wtmp respectively contain the currently logged in users, and the history of logins and logouts.
Each file is an array of the following structure defined in <utmp.h>:
struct utmp {
char ut_user[8]; /* user name */
char ut_line[12]; /* terminal name */
char ut_host[16]; /* host name, when remote */
time_t ut_time; /* login/logout time */
};
#define ut_name ut_user/* for compatibility with other systems */
The structure contains more fields than those listed, but they are only of interest to init and login. Note that the ut_name field is a
compatibility alias for ut_user, it is actually better to use it.
A login entry is completely specified. A logout entry has a null string for ut_name. A shutdown or reboot entry has an ut_line field con-
taining a "~" (tilde). The ut_name field is usually the name of the program that did the shutdown, or "reboot" at reboot. This is a bit
confusing, but note that there should always be two such entries. If you see just one entry then the system has crashed, if you see two
entries then the system was properly shut down and later rebooted.
FILES
/etc/utmp Currently logged in users.
/usr/adm/wtmp History of logins and logouts.
SEE ALSO who(1), ttyslot(3).
AUTHOR
Kees J. Bot (kjb@cs.vu.nl)
UTMP(5)
Check Out this Related Man Page
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.
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 '|' 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.
BSD May 14, 2003 BSD