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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 dif-
       fer (consult 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 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 cur-
       rent login activity; and getpwuid( getuid()) shall return the name associated with the real user ID of the pro-
       cess.

       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 getlo-
       gin() 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  overwrit-
       ten 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, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, 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(3P)