sysdeps/unix/getlogin.c

   1 /* Copyright (C) 1991-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <unistd.h>
  20 #include <string.h>
  21 #include <stdio.h>
  22 #include <limits.h>
  23 #include <fcntl.h>
  24
  25 #include <utmp.h>
  26
  27 static char name[UT_NAMESIZE + 1];
  28
  29 /* Return the login name of the user, or NULL if it can't be determined.
  30    The returned pointer, if not NULL, is good only until the next call.  */
  31
  32 #ifdef STATIC
  33 STATIC
  34 #endif
  35 char *
  36 getlogin (void)
  37 {
  38   char tty_pathname[2 + 2 * NAME_MAX];
  39   char *real_tty_path = tty_pathname;
  40   int err;
  41   char *result = NULL;
  42   struct utmp *ut, line, buffer;
  43
  44   /* Get name of tty connected to fd 0.  Return NULL if not a tty or
  45      if fd 0 isn't open.  Note that a lot of documentation says that
  46      getlogin() is based on the controlling terminal---what they
  47      really mean is "the terminal connected to standard input".  The
  48      getlogin() implementation of DEC Unix, SunOS, Solaris, HP-UX all
  49      return NULL if fd 0 has been closed, so this is the compatible
  50      thing to do.  Note that ttyname(open("/dev/tty")) on those
  51      systems returns /dev/tty, so that is not a possible solution for
  52      getlogin().  */
  53   err = __ttyname_r (0, real_tty_path, sizeof (tty_pathname));
  54   if (err != 0)
  55     {
  56       __set_errno (err);
  57       return NULL;
  58     }
  59
  60   real_tty_path += 5;           /* Remove "/dev/".  */
  61
  62   __setutent ();
  63   strncpy (line.ut_line, real_tty_path, sizeof line.ut_line);
  64   if (__getutline_r (&line, &buffer, &ut) < 0)
  65     {
  66       if (errno == ESRCH)
  67         /* The caller expects ENOENT if nothing is found.  */
  68         __set_errno (ENOENT);
  69       result = NULL;
  70     }
  71   else
  72     {
  73       strncpy (name, ut->ut_user, UT_NAMESIZE);
  74       name[UT_NAMESIZE] = '\0';
  75       result = name;
  76     }
  77
  78   __endutent ();
  79
  80   return result;
  81 }