LINK(2) System Calls LINK(2)
NAME
link, linkat - link to a file
SYNOPSIS
#include <unistd.h>
int link(
const char *existing,
const char *new);
int linkat(
int efd,
const char *existing,
int nfd,
const char *new,
int flag);
DESCRIPTION
The
link() and
linkat() functions create a new link (directory entry)
for the existing file and increments its link count by one. The
existing argument points to a path name naming an existing file. The
new argument points to a pathname naming the new directory entry to
be created.
To create hard links, both files must be on the same file system.
Both the old and the new link share equal access and rights to the
underlying object. Privileged processes can make multiple links to a
directory. Unless the caller is privileged, the file named by
existing must not be a directory.
The
linkat() function is similar to
link(). If the path
existing is a
relative path, then the directory represented by
efd will be used as
the starting point to resolve
existing. If the path
new is a relative
path, then the directory represented by
nfd will be used as the
starting point to resolve
new. Both
efd and
nfd may be the special
value
AT_FDCWD which causes the current working directory to be used
as the starting point for path resolution.
By default,
linkat() does not follow symbolic links. To cause it to
follow symbolic links, the value of
flag should be
AT_SYMLINK_FOLLOW.
Upon successful completion,
link() and
linkat() 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 are marked for update.
RETURN VALUES
Upon successful completion,
0 is returned. Otherwise,
-1 is returned,
no link is created, and
errno is set to indicate the error.
ERRORS
The
link() and
linkat() functions will fail if:
EACCES A component of either path prefix denies search
permission, or the requested link requires writing in
a directory with a mode that denies write permission.
EDQUOT The directory where the entry for the new link is
being placed cannot be extended because the user's
quota of disk blocks on that file system has been
exhausted.
EEXIST The link named by
new exists.
EFAULT The
existing or
new argument points to an illegal
address.
EILSEQ The path argument includes non-UTF8 characters and
the file system accepts only file names where all
characters are part of the UTF-8 character codeset.
EINTR A signal was caught during the execution of the
link() or
linkat() functions.
ELOOP Too many symbolic links were encountered in
translating
path.
EMLINK The maximum number of links to a file would be
exceeded.
ENAMETOOLONG The length of the
existing or
new argument exceeds
PATH_MAX, or the length of a
existing or
new component exceeds
NAME_MAX while
_POSIX_NO_TRUNC is
in effect.
ENOENT The
existing or
new argument is a null pathname; a
component of either path prefix does not exist; or
the file named by
existing does not exist.
ENOLINK The
existing or
new argument points to a remote
machine and the link to that machine is no longer
active.
ENOSPC The directory that would contain the link cannot be
extended.
ENOTDIR A component of either path prefix is not a directory.
EPERM The file named by
existing is a directory and the
{
PRIV_SYS_LINKDIR} privilege is not asserted in the
effective set of the calling process.
The effective user ID does not match the owner of the
file and the {
PRIV_FILE_LINK_ANY} privilege is not
asserted in the effective set of the calling process.
EROFS The requested link requires writing in a directory on
a read-only file system.
EXDEV The link named by
new and the file named by
existing are on different logical devices (file systems).
The
linkat() functions will fail if:
EBADF If either
existing or
new is a relative path and
efd or
nfd respectively are not a valid file descriptor
or the value
AT_FDCWD.
EINVAL An invalid value is set in
flag. The only valid
values are
0 and
fBAT_SYMLINK_FOLLOW.
ENOTDIR If either
existing or
new is a relative path and
efd or
nfd respectively refer to a valid descriptor which
is not a directory.
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Standard |
+--------------------+-------------------+
|MT-Level | Async-Signal-Safe |
+--------------------+-------------------+
SEE ALSO
symlink(2),
unlink(2),
attributes(7),
privileges(7),
standards(7) May 18, 2007 LINK(2)
