UTMP(5) | File Formats Manual | UTMP(5) |
utmp
, wtmp
,
lastlog
— login
records
#include
<utmp.h>
The <utmp.h>
file
declares the structures used to record information about current users in
the utmp
file, logins and logouts in the
wtmp
file, and last logins in the
lastlog
file. The timestamps of date changes,
shutdowns, and reboots are also logged in the wtmp
file.
wtmp
can grow rapidly on busy systems, so
daily or weekly rotation is recommended. If any one of these files does not
exist, it is not created. They must be created manually and are maintained
by newsyslog(8).
#define _PATH_UTMP "/var/run/utmp" #define _PATH_WTMP "/var/log/wtmp" #define _PATH_LASTLOG "/var/log/lastlog" #define UT_NAMESIZE 32 #define UT_LINESIZE 8 #define UT_HOSTSIZE 256 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 lastlog
file. 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 (provided the login is not
“quiet”; see
login(1)). The
login(1) program then records
the new login time in the lastlog
file.
After the new lastlog record is written, the
utmp
file is opened and the
utmp record for the user is inserted. This record
remains until the user logs out at which time it is deleted. The
utmp
file is used by the programs
users(1),
w(1), and
who(1).
Next, the login(1)
program opens the wtmp
file and appends the user's
utmp record. When the user logs out, a
utmp record with the tty line, an updated timestamp,
and zeroed name and host fields is appended to the file (see
init(8)). The
wtmp
file is used by the programs
last(1) and
ac(8).
In the event of a date change, shutdown, or reboot, the following
items are logged in the wtmp
file:
reboot
shutdown
date
A utmp
and wtmp
file format appeared in Version 3 AT&T
UNIX. The lastlog
file format appeared in
3.0BSD.
The strings in the utmp and lastlog structures are not normal ‘C’ strings and are thus not guaranteed to be null terminated.
September 10, 2015 | OpenBSD-6.5 |