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

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

       getlogin, getlogin_r — get login name

       #include <unistd.h>

       char *getlogin(void);
       int getlogin_r(char *name, size_t namesize);

       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 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.

       The getlogin() and getlogin_r() functions may make use of file descrip‐
       tors 0, 1, and 2 to  find  the  controlling  terminal  of  the  current
       process, examining each in turn until the terminal is found. If in this
       case none of these three file descriptors is open  to  the  controlling
       terminal,  these functions may fail. The method used to find the termi‐
       nal associated with a file descriptor may depend on the file descriptor
       being open to the actual terminal device, not /dev/tty.

       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

       The application shall not modify	 the  string  returned.	 The  returned
       pointer might be invalidated or the string content might be overwritten
       by a subsequent call to getlogin().

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

       These functions may fail if:

       EMFILE All  file	 descriptors  available	 to  the process are currently

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

       ENOTTY None  of the file descriptors 0, 1, or 2 is open to the control‐
	      ling terminal of the current process.

       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.

   Getting the User Login Name S
       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

	   #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);

       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.

       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:


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


       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.


       getpwnam(), getpwuid(), geteuid(), getuid()

       The Base Definitions volume of POSIX.1‐2008, <limits.h>, <unistd.h>

       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal and Electronics Engineers,  Inc  and	 The  Open  Group.   (This  is
       POSIX.1-2008  with  the	2013  Technical Corrigendum 1 applied.) 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 .

       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker‐ .

IEEE/The Open Group		     2013			  GETLOGIN(3P)

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