|
HTML rendering created 2025-02-02 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. |
|
|
PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
|
|
|
SYMLINK(3P) POSIX Programmer's Manual SYMLINK(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.
symlink, symlinkat — make a symbolic link
#include <unistd.h>
int symlink(const char *path1, const char *path2);
#include <fcntl.h>
int symlinkat(const char *path1, int fd, const char *path2);
The symlink() function shall create a symbolic link called path2
that contains the string pointed to by path1 (path2 is the name of
the symbolic link created, path1 is the string contained in the
symbolic link).
The string pointed to by path1 shall be treated only as a 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. Implementations 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 timestamps 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 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 symlinkat() 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 symlink().
Upon successful completion, these functions shall return 0.
Otherwise, these functions shall return -1 and set errno to
indicate the error.
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 component 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
existing file or path2 is an empty string.
ENOENT or ENOTDIR
The path2 argument contains at least one non-<slash>
character and ends with one or more trailing <slash>
characters. If path2 without the trailing <slash>
characters would name an existing file, an [ENOENT] error
shall not occur.
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 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 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.
None.
Like a hard link, a symbolic link allows a file to have multiple
logical 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 argument 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.
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 symlinkat() function it can
be guaranteed that the created symbolic link is located relative
to the desired directory.
None.
fdopendir(3p), fstatat(3p), lchown(3p), link(3p), open(3p),
readlink(3p), rename(3p), unlink(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 SYMLINK(3P)
Pages that refer to this page: unistd.h(0p), fdopendir(3p), fstatat(3p), lchown(3p), link(3p), open(3p), readdir(3p), readlink(3p), rename(3p), unlink(3p)
|
HTML rendering created 2025-02-02 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. |
|