Originální popis anglicky:
link - link to a file
Návod, kniha: POSIX Programmer's Manual
#include <unistd.h>
int link(const char *
path1, const char
*path2 );
The
link() function shall create a new link (directory entry) for the
existing file,
path1.
The
path1 argument points to a pathname naming an existing file. The
path2 argument points to a pathname naming the new directory entry to
be created. The
link() function shall atomically create a new link for
the existing file and the link count of the file shall be incremented by one.
If
path1 names a directory,
link() shall fail unless the process
has appropriate privileges and the implementation supports using
link()
on directories.
Upon successful completion,
link() shall mark for update the
st_ctime field of the file. Also, the
st_ctime and
st_mtime fields of the directory that contains the new entry shall be
marked for update.
If
link() fails, no link shall be created and the link count of the file
shall remain unchanged.
The implementation may require that the calling process has permission to access
the existing file.
Upon successful completion, 0 shall be returned. Otherwise, -1 shall be returned
and
errno set to indicate the error.
The
link() function shall fail if:
- EACCES
- A component of either path prefix denies search permission,
or the requested link requires writing in a directory that denies write
permission, or the calling process does not have permission to access the
existing file and this is required by the implementation.
- EEXIST
- The path2 argument resolves to an existing file or
refers to a symbolic link.
- ELOOP
- A loop exists in symbolic links encountered during
resolution of the path1 or path2 argument.
- EMLINK
- The number of links to the file named by path1 would
exceed {LINK_MAX}.
- ENAMETOOLONG
- The length of the path1 or path2 argument
exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.
- ENOENT
- A component of either path prefix does not exist; the file
named by path1 does not exist; or path1 or path2
points to an empty string.
- ENOSPC
- The directory to contain the link cannot be extended.
- ENOTDIR
- A component of either path prefix is not a directory.
- EPERM
- The file named by path1 is a directory and either
the calling process does not have appropriate privileges or the
implementation prohibits using link() on directories.
- EROFS
- The requested link requires writing in a directory on a
read-only file system.
- EXDEV
- The link named by path2 and the file named by
path1 are on different file systems and the implementation does not
support links between file systems.
- EXDEV
- path1 refers to a named STREAM.
The
link() function may fail if:
- ELOOP
- More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the path1 or path2 argument.
- ENAMETOOLONG
- As a result of encountering a symbolic link in resolution
of the path1 or path2 argument, the length of the
substituted pathname string exceeded {PATH_MAX}.
The following sections are informative.
The following example shows how to create a link to a file named
/home/cnd/mod1 by creating a new directory entry named
/modules/pass1.
#include <unistd.h>
char *path1 = "/home/cnd/mod1";
char *path2 = "/modules/pass1";
int status;
...
status = link (path1, path2);
In the following program example, the
link() function links the
/etc/passwd file (defined as
PASSWDFILE) to a file named
/etc/opasswd (defined as
SAVEFILE), which is used to save the
current password file. Then, after removing the current password file (defined
as
PASSWDFILE), the new password file is saved as the current password
file using the
link() function again.
#include <unistd.h>
#define LOCKFILE "/etc/ptmp"
#define PASSWDFILE "/etc/passwd"
#define SAVEFILE "/etc/opasswd"
...
/* Save current password file */
link (PASSWDFILE, SAVEFILE);
/* Remove current password file. */
unlink (PASSWDFILE);
/* Save new password file as current password file. */
link (LOCKFILE,PASSWDFILE);
Some implementations do allow links between file systems.
Linking to a directory is restricted to the superuser in most historical
implementations because this capability may produce loops in the file
hierarchy or otherwise corrupt the file system. This volume of
IEEE Std 1003.1-2001 continues that philosophy by prohibiting
link() and
unlink() from doing this. Other functions could do it
if the implementor designed such an extension.
Some historical implementations allow linking of files on different file
systems. Wording was added to explicitly allow this optional behavior.
The exception for cross-file system links is intended to apply only to links
that are programmatically indistinguishable from "hard" links.
None.
symlink() ,
unlink() , the Base Definitions volume of
IEEE Std 1003.1-2001,
<unistd.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 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
.
