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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).

     allbox; lb lb lbw20 l l l.  Interface Attribute Value T{ login(),
     logout() T}   Thread safety  T{ MT-Unsafe race:utent
     sig:ALRM timer T}

     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>.