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(5) 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(5), privileges(5), standards(5)


May 18, 2007 LINK(2)