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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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READLINK(3P) POSIX Programmer's Manual READLINK(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.
readlink, readlinkat — read the contents of a symbolic link
#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);
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().
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.
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.
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';
Conforming applications should not assume that the returned
contents of the symbolic link are null-terminated.
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.
None.
fstatat(3p), symlink(3p)
The Base Definitions volume of POSIX.1‐2017, fcntl.h(0p),
unistd.h(0p)
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 .
IEEE/The Open Group 2017 READLINK(3P)
Pages that refer to this page: unistd.h(0p), fstatat(3p), symlink(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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