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

       login, logout - write utmp and wtmp entries

       #include <utmp.h>

       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 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.

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

              user accounting database, configured through _PATH_UTMP in

              user accounting log file, configured through _PATH_WTMP in

       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.

       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>.

       getutent(3), utmp(5)

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       latest version of this page, can be found at

GNU                               2017-09-15                          LOGIN(3)