symlink

SYMLINK(3POSIX)             POSIX Programmer's Manual            SYMLINK(3POSIX)



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
       symbolic 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.
       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
       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 parameter,
       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
              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.

       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 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.

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
       symlinkat() 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 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
       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.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                   2013                       SYMLINK(3POSIX)