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link, linkat — make a hard file link
Standard C Library (libc, -lc)
link(const char *name1, const char *name2);
linkat(int fd1, const char *name1, int fd2, const char *name2, int flag);
The link() system call atomically creates the specified directory entry
(hard link) name2 with the attributes of the underlying object pointed at
by name1. If the link is successful: the link count of the underlying
object is incremented; name1 and name2 share equal access and rights to
the underlying object.
If name1 is removed, the file name2 is not deleted and the link count of
the underlying object is decremented.
The object pointed at by the name1 argument must exist for the hard link
to succeed and both name1 and name2 must be in the same file system. The
name1 argument may not be a directory.
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>:
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.
The link() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
The link() system call will fail and no link will be created if:
[ENOTDIR] A component of either path prefix is not a directory.
[ENAMETOOLONG] A component of either pathname exceeded 255
characters, or entire length of either path name
exceeded 1023 characters.
[ENOENT] A component of either path prefix does not exist.
[EOPNOTSUPP] The file system containing the file named by name1
does not support links.
[EMLINK] The link count of the file named by name1 would exceed
[EACCES] A component of either path prefix denies search
[EACCES] The requested link requires writing in a directory
with a mode that denies write permission.
[ELOOP] Too many symbolic links were encountered in
translating one of the pathnames.
[ENOENT] The file named by name1 does not exist.
[EEXIST] The link named by name2 does exist.
[EPERM] The file named by name1 is a directory.
[EPERM] The file named by name1 has its immutable or append-
only flag set, see the chflags(2) manual page for more
[EPERM] The parent directory of the file named by name2 has
its immutable flag set.
[EXDEV] The link named by name2 and the file named by name1
are on different file systems.
[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
[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.
[EIO] An I/O error occurred while reading from or writing to
the file system to make the directory entry.
[EROFS] The requested link requires writing in a directory on
a read-only file system.
[EFAULT] One of the pathnames specified is outside the
process's allocated address space.
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.
[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.
chflags(2), readlink(2), symlink(2), unlink(2)
The link() system call is expected to conform to ISO/IEC 9945-1:1990
(“POSIX.1”). The linkat() system call follows The Open Group Extended
API Set 2 specification.
The link() function appeared in Version 7 AT&T UNIX. The linkat() system
call appeared in FreeBSD 8.0.
The link() system call traditionally allows the super-user to link
directories which corrupts the file system coherency. This
implementation no longer permits it.