#### 31.12.3 Logging In and Out ¶

These functions, derived from BSD, are available in the separate `libutil` library, and declared in `utmp.h`.

Note that the `ut_user` member of `struct utmp` is called `ut_name` in BSD. Therefore, `ut_name` is defined as an alias for `ut_user` in `utmp.h`.

Function: `int` login_tty `(int filedes)` ¶

  Preliminary: | MT-Unsafe race:ttyname | AS-Unsafe heap lock | AC-Unsafe lock fd mem | See POSIX Safety Concepts.

  This function makes filedes the controlling terminal of the current process, redirects standard input, standard output and standard error output to this terminal, and closes filedes.

  This function returns `0` on successful completion, and `-1` on error.

Function: `void` login `(const struct utmp *entry)` ¶

  Preliminary: | MT-Unsafe race:utent sig:ALRM timer | AS-Unsafe lock heap | AC-Unsafe lock corrupt fd mem | See POSIX Safety Concepts.

  The `login` functions inserts an entry into the user accounting database. The `ut_line` member is set to the name of the terminal on standard input. If standard input is not a terminal `login` uses standard output or standard error output to determine the name of the terminal. If `struct utmp` has a `ut_type` member, `login` sets it to `USER_PROCESS`, and if there is an `ut_pid` member, it will be set to the process ID of the current process. The remaining entries are copied from entry.

  A copy of the entry is written to the user accounting log file.

Function: `int` logout `(const char *ut_line)` ¶

  Preliminary: | MT-Unsafe race:utent sig:ALRM timer | AS-Unsafe lock heap | AC-Unsafe lock fd mem | See POSIX Safety Concepts.

  This function modifies the user accounting database to indicate that the user on ut_line has logged out.

  The `logout` function returns `1` if the entry was successfully written to the database, or `0` on error.

Function: `void` logwtmp `(const char *ut_line, const char *ut_name, const char *ut_host)` ¶

  Preliminary: | MT-Unsafe sig:ALRM timer | AS-Unsafe | AC-Unsafe fd | See POSIX Safety Concepts.

  The `logwtmp` function appends an entry to the user accounting log file, for the current time and the information provided in the ut_line, ut_name and ut_host arguments.

Portability Note: The BSD `struct utmp` only has the `ut_line`, `ut_name`, `ut_host` and `ut_time` members. Older systems do not even have the `ut_host` member.