utmp(5)
Name
utmp, wtmp − login records
Syntax
#include <utmp.h>
Description
The utmp file records information about who is currently using the system. The file is a sequence of entries with the following structure declared in the include file:
struct utmp {
char ut_line[8]; /* tty name */
char ut_name[8]; /* user id */
char ut_host[16]; /* host name, if remote */
long ut_time; /* time on */
};
This structure gives the name of the special file associated with the user’s terminal, the user’s login name, and the time of the login in the form of time(.).
The wtmp file records all logins and logouts. A null user name indicates a logout on the associated terminal. A terminal referenced with a tilde (~) indicates that the system was rebooted at the indicated time. The adjacent pair of entries with terminal names referenced by a vertical bar (|) or a right brace (}) indicate the system-maintained time just before and just after a date command has changed the system’s timeframe.
The wtmp file is maintained by login() and init(.). Neither of these programs creates the file, so, if it is removed, record-keeping is turned off. It is summarized by ac(.).
Files
/etc/utmp
/usr/adm/wtmp