/*
* Structure of utmp and wtmp files.
*
* Assuming the number 8 is unwise.
*/
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 is a utmp entry that does not correspond to a genuine user
*/
#define nonuser(ut) ((ut).ut_host[0] == 0 && \
strncmp((ut).ut_line, "tty", 3) == 0 && ((ut).ut_line[3] == 'p' \
|| (ut).ut_line[3] == 'q' \
|| (ut).ut_line[3] == 'r' \
|| (ut).ut_line[3] == 's'))
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(3C).
The wtmp file records all logins and logouts. A null user name indicates a logout on the associated terminal. Furthermore, the terminal name `~' indicates that the system was rebooted at the indicated time; the adjacent pair of entries with terminal names `|' and `{' indicate the system-maintained time just before and just after a date command has changed the system's idea of the time.
Wtmp is maintained by login(1) and init(8). Neither of these programs creates the file, so if it is removed record-keeping is turned off. It is summarized by ac(8).