LOGIN(3)                  Linux Programmer's Manual                 LOGIN(3)

NAME         top

       login, logout - write utmp and wtmp entries

SYNOPSIS         top

       #include <utmp.h>

       void login(const struct utmp *ut);

       int logout(const char *ut_line);

       Link with -lutil.

DESCRIPTION         top

       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.

   GNU details
       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.

RETURN VALUE         top

       The logout() function returns 1 if the entry was successfully written
       to the database, or 0 if an error occurred.

FILES         top

              user accounting database, configured through _PATH_UTMP in

              user accounting log file, configured through _PATH_WTMP in

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface Attribute     Value                │
       │login(),  │ Thread safety │ MT-Unsafe race:utent │
       │logout()  │               │ 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.

CONFORMING TO         top

       Not in POSIX.1.  Present on the BSDs.

NOTES         top

       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>.

SEE ALSO         top

       getutent(3), utmp(5)

COLOPHON         top

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GNU                              2016-10-08                         LOGIN(3)