login, logout - write utmp and wtmp entries
void login(const struct utmp *ut);
int logout(const char *ut_line);
Link with -lutil.
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
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.
For an explanation of the terms used in this section, see attributes(7).
- user accounting database, configured through _PATH_UTMP in
- user accounting log file, configured through _PATH_WTMP in
|login (), logout ()
||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.
Not in POSIX.1. Present on the BSDs.
Note that 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>.
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