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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);

       #include <fcntl.h>

       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 access mode of the open file description associated with
       the file descriptor is not O_SEARCH, the function shall check whether  directory  searches
       are  permitted  using  the  current  permissions  of  the  directory  underlying  the file
       descriptor. If the access mode is 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 The access mode of the open file description associated with fd is not 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
       1003.1-2017,  Standard  for  Information Technology -- Portable Operating System Interface
       (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C)  2018  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
       Standard,  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 .

       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 .