GETLOGIN(3P)                                        POSIX Programmer's Manual                                       GETLOGIN(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

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  cur-
       rent  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 char-
              acter.


       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 subse-
       quently 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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                  GETLOGIN(3P)