login, logout - write utmp and wtmp entries
System utilities library (libutil, -lutil)
#include <utmp.h>
void login(const struct utmp *ut);
int logout(const char *ut_line);The utmp file records who is currently using the system. The wtmp file records all logins and logouts. See utmp(5).
The function login() takes the supplied struct
utmp, ut, and writes it to both the utmp and the wtmp
file.
The function logout() clears the entry in the utmp file again.
More precisely, login() takes the argument
ut struct, fills the field ut->ut_type (if there is
such a field) with the value USER_PROCESS, and fills
the field ut->ut_pid (if there is such a field) with the
process ID of the calling process. Then it tries to fill the field
ut->ut_line. It takes the first of stdin,
stdout, stderr that is a terminal, and stores the
corresponding pathname minus a possible leading /dev/ into this
field, and then writes the struct to the utmp file. On the other hand,
if no terminal name was found, this field is filled with "???" and the
struct is not written to the utmp file. After this, the struct is
written to the wtmp file.
The logout() function searches the utmp file for an
entry matching the ut_line argument. If a record is found, it
is updated by zeroing out the ut_name and ut_host
fields, updating the ut_tv timestamp field and setting
ut_type (if there is such a field) to
DEAD_PROCESS.
The logout() function returns 1 if the entry was successfully written to the database, or 0 if an error occurred.
/var/run/utmpuser accounting database, configured through
_PATH_UTMP in <paths.h>
/var/log/wtmpuser accounting log file, configured through
_PATH_WTMP in <paths.h>
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
| Thread safety | MT-Unsafe race:utent sig:ALRM timer |
In the above table, utent in race:utent signifies
that if any of the functions setutent(3),
getutent(3), or endutent(3) are used
in parallel in different threads of a program, then data races could
occur. login() and logout() calls
those functions, so we use race:utent to remind users.
The member ut_user of struct utmp is called
ut_name in BSD. Therefore, ut_name is defined as an
alias for ut_user in <utmp.h>.
BSD.