− write utmp and wtmp entries
login(const struct utmp *ut);
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).
login() takes the supplied struct utmp,
ut, and writes it to both the utmp and the wtmp
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.
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)
logout() function returns 1 if the entry was
successfully written to the database, or 0 if an error
user accounting database,
configured through _PATH_UTMP in
user accounting log file,
configured through _PATH_WTMP in
explanation of the terms used in this section, see
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(3) and logout(3) 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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