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

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 char‐
       acter. 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 infor‐
       mation  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: get‐
       pwuid(  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, par‐
       ticularly  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	origi‐
       nally  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)
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