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READLINK(3P)               POSIX Programmer's Manual              READLINK(3P)
PROLOG
       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.
NAME
       readlink, readlinkat -- read the contents of a symbolic link
SYNOPSIS
       #include <unistd.h>
       ssize_t readlink(const char *restrict path, char *restrict buf,
           size_t bufsize);
       ssize_t readlinkat(int fd, const char *restrict path,
           char *restrict buf, size_t bufsize);
DESCRIPTION
       The readlink() function shall place the contents of the  symbolic  link
       referred  to  by path in the buffer buf which has size bufsize.  If the
       number of bytes in the symbolic link is less than bufsize, the contents
       of  the  remainder  of  buf are unspecified. If the buf argument is not
       large enough to contain the link content, the first bufsize bytes shall
       be placed in buf.
       If  the  value  of  bufsize  is greater than {SSIZE_MAX}, the result is
       implementation-defined.
       Upon successful completion, readlink() shall mark for update  the  last
       data access timestamp of the symbolic link.
       The  readlinkat()  function shall be equivalent to the readlink() func-
       tion except in the case where path specifies a relative path.  In  this
       case  the symbolic link whose content is read is relative to the direc-
       tory associated with the file descriptor  fd  instead  of  the  current
       working  directory. If the file descriptor was opened without O_SEARCH,
       the function shall check whether directory searches are permitted using
       the  current  permissions of the directory underlying the file descrip-
       tor. If the file descriptor was  opened  with  O_SEARCH,  the  function
       shall not perform the check.
       If  readlinkat() is passed the special value AT_FDCWD in the fd parame-
       ter, the current working directory shall be used and the behavior shall
       be identical to a call to readlink().
RETURN VALUE
       Upon  successful  completion, these functions shall return the count of
       bytes placed in the buffer. Otherwise, these functions shall  return  a
       value  of -1, leave the buffer unchanged, and set errno to indicate the
       error.
ERRORS
       These functions shall fail if:
       EACCES Search permission is denied for a component of the  path  prefix
              of path.
       EINVAL The path argument names a file that is not a symbolic link.
       EIO    An I/O error occurred while reading from the file system.
       ELOOP  A loop exists in symbolic links encountered during resolution of
              the path argument.
       ENAMETOOLONG
              The  length  of  a  component  of  a  pathname  is  longer  than
              {NAME_MAX}.
       ENOENT A component of path does not name an existing file or path is an
              empty string.
       ENOTDIR
              A component of the path prefix names an existing  file  that  is
              neither  a  directory nor a symbolic link to a directory, or the
              path argument contains at least one  non-<slash>  character  and
              ends  with  one or more trailing <slash> characters and the last
              pathname component names an existing  file  that  is  neither  a
              directory nor a symbolic link to a directory.
       The readlinkat() function shall fail if:
       EACCES fd  was  not  opened  with  O_SEARCH  and the permissions of the
              directory underlying fd do not permit directory searches.
       EBADF  The path argument does not specify an absolute path and  the  fd
              argument  is  neither  AT_FDCWD nor a valid file descriptor open
              for reading or searching.
       ENOTDIR
              The path argument is not an absolute  path  and  fd  is  a  file
              descriptor associated with a non-directory file.
       These functions may fail if:
       ELOOP  More  than  {SYMLOOP_MAX} symbolic links were encountered during
              resolution of the path argument.
       ENAMETOOLONG
              The length of a pathname exceeds {PATH_MAX}, or pathname resolu-
              tion  of  a symbolic link produced an intermediate result with a
              length that exceeds {PATH_MAX}.
       The following sections are informative.
EXAMPLES
   Reading the Name of a Symbolic Link
       The following example shows how to read the name  of  a  symbolic  link
       named /modules/pass1.
           #include <unistd.h>
           char buf[1024];
           ssize_t len;
           ...
           if ((len = readlink("/modules/pass1", buf, sizeof(buf)-1)) != -1)
               buf[len] = '\0';
APPLICATION USAGE
       Conforming applications should not assume that the returned contents of
       the symbolic link are null-terminated.
RATIONALE
       The type associated with bufsiz is a size_t in order to  be  consistent
       with  both the ISO C standard and the definition of read().  The behav-
       ior specified for readlink() when bufsiz is zero represents  historical
       practice.  For  this  case, the standard developers considered a change
       whereby readlink() would return the number of non-null bytes  contained
       in  the symbolic link with the buffer buf remaining unchanged; however,
       since the stat structure member st_size value can be used to  determine
       the  size  of  buffer necessary to contain the contents of the symbolic
       link as returned by readlink(), this proposal  was  rejected,  and  the
       historical practice retained.
       The purpose of the readlinkat() function is to read the content of sym-
       bolic links in directories other than  the  current  working  directory
       without  exposure  to  race conditions.  Any part of the path of a file
       could be changed in parallel to a  call  to  readlink(),  resulting  in
       unspecified  behavior.  By  opening  a  file  descriptor for the target
       directory and using the readlinkat() function it can be guaranteed that
       the symbolic link read is located relative to the desired directory.
FUTURE DIRECTIONS
       None.
SEE ALSO
       fstatat(), symlink()
       The Base Definitions volume of POSIX.1-2008, <unistd.h>
COPYRIGHT
       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 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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                         READLINK(3P)