NAME
link
, linkat
— make a hard file
link
SYNOPSIS
#include
<unistd.h>
int
link
(const char *path1,
const char *path2);
int
linkat
(int fd1,
const char *name1, int fd2,
const char *name2, int
flag);
DESCRIPTION
The
link
()
function call atomically creates the specified directory entry (hard link)
path2 with the attributes of the underlying object
pointed at by path1. If the link is successful, the
link count of the underlying object is incremented;
path1 and path2 share equal
access and rights to the underlying object.
If path1 is removed, the file path2 is not deleted and the link count of the underlying object is decremented.
In order for the system call to succeed, path1 must exist and both path1 and path2 must be in the same file system. As mandated by POSIX.1, path1 may not be a directory.
link
()
will resolve and follow symbolic links contained within both
path1 and path2. If the last
component of path1 is a symbolic link,
link
() will point the hard link,
path2, to the underlying object pointed to by
path1, not to the symbolic link itself.
The
linkat
()
system call is equivalent to link except in the case
where either name1 or name2 or
both are relative paths. In this case a relative path
name1 is interpreted relative to the directory
associated with the file descriptor fd1 instead of the
current working directory and similarly for name2 and
the file descriptor fd2.
Values for flag are constructed by a
bitwise-inclusive OR of flags from the following list, defined in
<fcntl.h>
:
AT_SYMLINK_FOLLOW
- If name1 names a symbolic link, a new link for the target of the symbolic link is created.
If
linkat
()
is passed the special value AT_FDCWD
in the
fd1 or fd2 parameter, the
current working directory is used for the respective
name argument. If both fd1 and
fd2 have value AT_FDCWD
, the
behavior is identical to a call to link
(). Unless
flag contains the
AT_SYMLINK_FOLLOW
flag, if
name1 names a symbolic link, a new link is created for
the symbolic link name1 and not its target. On OS X,
not assigning AT_SYMLINK_FOLLOW to flag may result in
some file systems returning an error.
RETURN VALUES
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.
ERRORS
link
() will fail and no link will be
created if:
- [
EACCES
] - A component of either path prefix denies search permission.
- [
EACCES
] - The requested link requires writing in a directory with a mode that denies write permission.
- [
EACCES
] - The current process cannot access the existing file.
- [
EDQUOT
] - The directory in which the entry for the new link is being placed cannot be extended because the user's quota of disk blocks on the file system containing the directory has been exhausted.
- [
EEXIST
] - The link named by path2 already exists.
- [
EFAULT
] - One of the pathnames specified is outside the process's allocated address space.
- [
EIO
] - An I/O error occurs while reading from or writing to the file system to make the directory entry.
- [
ELOOP
] - Too many symbolic links are encountered in translating one of the pathnames. This is taken to be indicative of a looping symbolic link.
- [
EMLINK
] - The file already has {LINK_MAX} links.
- [
ENAMETOOLONG
] - A component of a pathname exceeds
{NAME_MAX}
characters, or an entire path name exceeded{PATH_MAX}
characters. - [
ENOENT
] - A component of either path prefix does not exist, or is a dangling symbolic link.
- [
ENOENT
] - The file named by path1 does not exist, or is a dangling symbolic link.
- [
ENOSPC
] - The directory in which the entry for the new link is being placed cannot be extended because there is no space left on the file system containing the directory.
- [
ENOTDIR
] - A component of either path prefix is not a directory.
- [
EPERM
] - The file named by path1 is a directory.
- [
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.
- [
EDEADLK
] - The file named by path1 is a “dataless” file that must be materialized before being linked and the I/O policy of the current thread or process disallows file materialization (see getiopolicy_np(3)).
In addition to the errors returned by the
link
(), the linkat
() system
call may fail if:
- [
EBADF
] - The name1 or name2 argument
does not specify an absolute path and the fd1 or
fd2 argument, respectively, is neither
AT_FDCWD
nor a valid file descriptor open for searching. - [
EINVAL
] - The value of the flag argument is not valid.
- [
ENOTSUP
] - flag was not set to
AT_SYMLINK_FOLLOW (some file systems only).
- [
ENOTSUP
] - The underlying file system does not support this call.
- [
ENOTDIR
] - The name1 or name2 argument is
not an absolute path and fd1 or
fd2, respectively, is neither
AT_FDCWD
nor a file descriptor associated with a directory.
SEE ALSO
STANDARDS
The link
() function is expected to conform
to IEEE Std 1003.1-1988 (“POSIX.1”).
The linkat
() system call is expected to conform to
POSIX.1-2008 .