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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
   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

   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 4.09 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/.



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