SYMLINK(3P) POSIX Programmer's Manual SYMLINK(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
symlink, symlinkat -- make a symbolic link relative to directory file
descriptor
SYNOPSIS
#include <unistd.h>
int symlink(const char *path1, const char *path2);
int symlinkat(const char *path1, int fd, const char *path2);
DESCRIPTION
The symlink() function shall create a symbolic link called path2 that
contains the string pointed to by path1 (path2 is the name of the sym-
bolic link created, path1 is the string contained in the symbolic
link).
The string pointed to by path1 shall be treated only as a character
string and shall not be validated as a pathname.
If the symlink() function fails for any reason other than [EIO], any
file named by path2 shall be unaffected.
If path2 names a symbolic link, symlink() shall fail and set errno to
[EEXIST].
The symbolic link's user ID shall be set to the process' effective user
ID. The symbolic link's group ID shall be set to the group ID of the
parent directory or to the effective group ID of the process. Implemen-
tations shall provide a way to initialize the symbolic link's group ID
to the group ID of the parent directory. Implementations may, but need
not, provide an implementation-defined way to initialize the symbolic
link's group ID to the effective group ID of the calling process.
The values of the file mode bits for the created symbolic link are
unspecified. All interfaces specified by POSIX.1-2008 shall behave as
if the contents of symbolic links can always be read, except that the
value of the file mode bits returned in the st_mode field of the stat
structure is unspecified.
Upon successful completion, symlink() shall mark for update the last
data access, last data modification, and last file status change time-
stamps of the symbolic link. Also, the last data modification and last
file status change timestamps of the directory that contains the new
entry shall be marked for update.
The symlinkat() function shall be equivalent to the symlink() function
except in the case where path2 specifies a relative path. In this case
the symbolic link is created 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 symlinkat() 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 symlink().
RETURN VALUE
Upon successful completion, these functions shall return 0. Otherwise,
these functions shall return -1 and set errno to indicate the error.
ERRORS
These functions shall fail if:
EACCES Write permission is denied in the directory where the symbolic
link is being created, or search permission is denied for a com-
ponent of the path prefix of path2.
EEXIST The path2 argument names an existing file.
EIO An I/O error occurs while reading from or writing to the file
system.
ELOOP A loop exists in symbolic links encountered during resolution of
the path2 argument.
ENAMETOOLONG
The length of a component of the pathname specified by the path2
argument is longer than {NAME_MAX} or the length of the path1
argument is longer than {SYMLINK_MAX}.
ENOENT A component of the path prefix of path2 does not name an exist-
ing file or path2 is an empty string.
ENOSPC The directory in which the entry for the new symbolic link is
being placed cannot be extended because no space is left on the
file system containing the directory, or the new symbolic link
cannot be created because no space is left on the file system
which shall contain the link, or the file system is out of file-
allocation resources.
ENOTDIR
A component of the path prefix of path2 names an existing file
that is neither a directory nor a symbolic link to a directory.
EROFS The new symbolic link would reside on a read-only file system.
The symlinkat() 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 path2 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 path2 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 path2 argument.
ENAMETOOLONG
The length of the path2 argument exceeds {PATH_MAX} or pathname
resolution of a symbolic link in the path2 argument produced an
intermediate result with a length that exceeds {PATH_MAX}.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
Like a hard link, a symbolic link allows a file to have multiple logi-
cal names. The presence of a hard link guarantees the existence of a
file, even after the original name has been removed. A symbolic link
provides no such assurance; in fact, the file named by the path1 argu-
ment need not exist when the link is created. A symbolic link can cross
file system boundaries.
Normal permission checks are made on each component of the symbolic
link pathname during its resolution.
RATIONALE
The purpose of the symlinkat() function is to create 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 symlink(), resulting in unspecified behavior. By
opening a file descriptor for the target directory and using the sym-
linkat() function it can be guaranteed that the created symbolic link
is located relative to the desired directory.
FUTURE DIRECTIONS
None.
SEE ALSO
fdopendir(), fstatat(), lchown(), link(), open(), readlink(), rename(),
unlink()
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 SYMLINK(3P)