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DESCRIPTION

#define _PATH_UTMP      "/var/run/utmp"
#define _PATH_WTMP      "/var/log/wtmp"
#define _PATH_LASTLOG   "/var/log/lastlog"

#define UT_NAMESIZE     16
#define UT_LINESIZE     8
#define UT_HOSTSIZE     16

struct lastlog {
        time_t  ll_time;		/* When user logged in */
        char    ll_line[UT_LINESIZE];	/* Terminal line name */
        char    ll_host[UT_HOSTSIZE];	/* Host user came from */
};

struct utmp {
        char    ut_line[UT_LINESIZE];	/* Terminal line name */
        char    ut_name[UT_NAMESIZE];	/* User's login name */
        char    ut_host[UT_HOSTSIZE];	/* Host user came from */
        time_t  ut_time;		/* When user logged in */
};

The lastlog file is a linear array of lastlog structures indexed by a user's UID. The utmp file is a linear array of utmp structures indexed by a terminal line number (see ttyslot(3)). The wtmp file consists of utmp structures and is a binary log file, that is, grows linearly at its end.

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 (unless the login is 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 is 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(1) program opens the file wtmp, and appends the user's utmp record. The user's subsequent logout from the terminal line is marked by a special utmp record with ut_line set accordingly, ut_time updated, but ut_name and ut_host both empty (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 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 (see 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.