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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() function except in the case where path
       specifies a relative path. In this case the symbolic link whose  content  is  read  is  relative  to  the
       directory  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 descriptor. 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 parameter, 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 resolution 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  behavior  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 symbolic 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.

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