NAME

       getlogin, getlogin_r - get login name

SYNOPSIS

       #include <unistd.h>

       char *getlogin(void);

       int getlogin_r(char *name, size_t namesize);

DESCRIPTION

       The  getlogin()  function  shall  return a pointer to a string containing the user name associated by the
       login activity with the controlling terminal of the current process. If  getlogin()  returns  a  non-null
       pointer,  then  that  pointer points to the name that the user logged in under, even if there are several
       login names with the same user ID.

       The getlogin() function need not be reentrant. A function that is not required to  be  reentrant  is  not
       required to be thread-safe.

       The  getlogin_r()  function  shall  put  the  name  associated by the login activity with the controlling
       terminal of the current process in the character  array  pointed  to  by  name.  The  array  is  namesize
       characters  long  and should have space for the name and the terminating null character. The maximum size
       of the login name is {LOGIN_NAME_MAX}.

       If getlogin_r() is successful, name points to the name the user used at login, even if there are  several
       login names with the same user ID.

RETURN VALUE

       Upon  successful completion, getlogin() shall return a pointer to the login name or a null pointer if the
       user's login name cannot be found. Otherwise, it shall return a null pointer and set  errno  to  indicate
       the error.

       The return value from getlogin() may point to static data whose content is overwritten by each call.

       If  successful, the getlogin_r() function shall return zero; otherwise, an error number shall be returned
       to indicate the error.

ERRORS

       The getlogin() and getlogin_r() functions may fail if:

       EMFILE {OPEN_MAX} file descriptors are currently open in the calling process.

       ENFILE The maximum allowable number of files is currently open in the system.

       ENXIO  The calling process has no controlling terminal.

       The getlogin_r() function may fail if:

       ERANGE The value of namesize is smaller than the length of  the  string  to  be  returned  including  the
              terminating null character.

       The following sections are informative.

EXAMPLES

   Getting the User Login Name
       The  following  example  calls the getlogin() function to obtain the name of the user associated with the
       calling process, and passes this information to the  getpwnam()  function  to  get  the  associated  user
       database information.

              #include <unistd.h>
              #include <sys/types.h>
              #include <pwd.h>
              #include <stdio.h>
              ...
              char *lgn;
              struct passwd *pw;
              ...
              if ((lgn = getlogin()) == NULL || (pw = getpwnam(lgn)) == NULL) {
                  fprintf(stderr, "Get of user information failed.\n"); exit(1);
                  }

APPLICATION USAGE

       Three  names associated with the current process can be determined: getpwuid( geteuid()) shall return the
       name associated with the effective user ID of the process; getlogin() shall return  the  name  associated
       with  the  current login activity; and getpwuid( getuid()) shall return the name associated with the real
       user ID of the process.

       The getlogin_r() function is thread-safe and returns values in a user-supplied buffer instead of possibly
       using a static data area that may be overwritten by each call.

RATIONALE

       The getlogin() function returns a pointer to the user's login name. The same user ID  may  be  shared  by
       several  login  names.  If  it  is  desired to get the user database entry that is used during login, the
       result of getlogin() should be used to provide the argument to the getpwnam() function.  (This  might  be
       used to determine the user's login shell, particularly where a single user has multiple login shells with
       distinct login names, but the same user ID.)

       The  information  provided  by  the  cuserid() function, which was originally defined in the POSIX.1-1988
       standard and subsequently removed, can be obtained by the following:

              getpwuid(geteuid())

       while the information provided by historical implementations of cuserid() can be obtained by:

              getpwuid(getuid())

       The thread-safe version of this function places the user name in a user-supplied  buffer  and  returns  a
       non-zero  value  if  it fails. The non-thread-safe version may return the name in a static data area that
       may be overwritten by each call.

FUTURE DIRECTIONS

       None.

SEE ALSO

       getpwnam() , getpwuid() , geteuid() , getuid() , the Base  Definitions  volume  of  IEEE Std 1003.1-2001,
       <limits.h>, <unistd.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc and The Open Group. In the event of any discrepancy between this version and the  original  IEEE  and
       The  Open  Group  Standard,  the  original  IEEE and The Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                                   2003                                           GETLOGIN(P)