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LOGIN(3)                   Linux Programmer's Manual                  LOGIN(3)
NAME
       login, logout - write utmp and wtmp entries
SYNOPSIS
       #include <utmp.h>
       void login(const struct utmp *ut);
       int logout(const char *ut_line);
       Link with -lutil.
DESCRIPTION
       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  lead-
       ing /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
       The  logout()  function returns 1 if the entry was successfully written
       to the database, or 0 if an error occurred.
FILES
       /var/run/utmp
              user  accounting  database,  configured  through  _PATH_UTMP  in
              <paths.h>
       /var/log/wtmp
              user  accounting  log  file,  configured  through  _PATH_WTMP in
              <paths.h>
ATTRIBUTES
       For  an  explanation  of  the  terms  used   in   this   section,   see
       attributes(7).
       +----------+---------------+----------------------+
       |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
       Not in POSIX.1.  Present on the BSDs.
NOTES
       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
       getutent(3), utmp(5)
COLOPHON
       This page is part of release 4.15 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.
GNU                               2017-09-15                          LOGIN(3)