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 (consult the correspond-
       ing 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 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.

       The getlogin() and getlogin_r() functions may make use of file descriptors 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 control-
       ling terminal, these functions may fail. The method used to find the terminal associated with a file descriptor	may  depend  on  the  file
       descriptor being open to the actual terminal device, not /dev/tty.

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 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.

ERRORS

       These functions may fail if:

       EMFILE All file descriptors available to the process are currently open.

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

       ENOTTY None of the file descriptors 0, 1, or 2 is open to the controlling 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.

EXAMPLES

   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
       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.
"); 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 POSIX.1-2008, <limits.h>, <unistd.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy  --	Portable  Operating  System  Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical 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 Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .

       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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE
/The Open Group						       2013							      GETLOGIN(3P)