Section: POSIX Programmer's Manual (3P)
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.
--- read the contents of a symbolic link
ssize_t readlink(const char *restrict path, char *restrict buf,
ssize_t readlinkat(int fd, const char *restrict path,
char *restrict buf, size_t bufsize);
function shall place the contents of the symbolic link referred to by
in the buffer
which has size
If the number of bytes in the symbolic link is less than
the contents of the remainder of
are unspecified. If the
argument is not large enough to contain the link content, the first
bytes shall be placed in
If the value of
is greater than
the result is implementation-defined.
Upon successful completion,
shall mark for update the last data access timestamp of the symbolic
function shall be equivalent to the
function except in the case where
specifies a relative path. In this case the symbolic link whose content
is read is relative to the directory associated with the file
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.
is passed the special value AT_FDCWD in the
parameter, the current working directory shall be used and the behavior
shall be identical to a call to
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
to indicate the error.
These functions shall fail if:
Search permission is denied for a component of the path prefix of
argument names a file that is not a symbolic link.
An I/O error occurred while reading from the file system.
A loop exists in symbolic links encountered during resolution of the
The length of a component of a pathname is longer than
A component of
does not name an existing file or
is an empty string.
A component of the path prefix names an existing file that is neither
a directory nor a symbolic link to a directory, or the
argument contains at least one non-<slash>
character and ends with one or more trailing
characters and the last pathname component names an existing file that
is neither a directory nor a symbolic link to a directory.
function shall fail if:
was not opened with O_SEARCH and the permissions of the directory
do not permit directory searches.
argument does not specify an absolute path and the
argument is neither AT_FDCWD nor a valid file descriptor open for reading
argument is not an absolute path and
is a file descriptor associated with a non-directory file.
These functions may fail if:
symbolic links were encountered during resolution of the
The length of a pathname exceeds
or pathname resolution of a symbolic link produced an intermediate
result with a length that exceeds
The following sections are informative.
Reading the Name of a Symbolic Link
The following example shows how to read the name of a symbolic link
if ((len = readlink("/modules/pass1", buf, sizeof(buf)-1)) != -1)
buf[len] = '\0';
Conforming applications should not assume that the returned contents of
the symbolic link are null-terminated.
The type associated with
in order to be consistent with both the ISO C standard and the definition of
The behavior specified for
is zero represents historical practice. For this case, the standard
developers considered a change whereby
would return the number of non-null bytes contained in the symbolic
link with the buffer
remaining unchanged; however, since the
value can be used to determine the size of buffer necessary to contain
the contents of the symbolic link as returned by
this proposal was rejected, and the historical practice retained.
The purpose of the
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
resulting in unspecified behavior. By opening a file descriptor for
the target directory and using the
function it can be guaranteed that the symbolic link read is located
relative to the desired directory.
The Base Definitions volume of POSIX.1-2008,
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
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