man linkat (2): make a hard file link

Other Alias

link

LIBRARY

Lb libc

SYNOPSIS

In unistd.h Ft int Fn link const char *name1 const char *name2 Ft int Fo linkat Fa int fd1 const char *name1 int fd2 const char *name2 int flag Fc

DESCRIPTION

The Fn link system call atomically creates the specified directory entry (hard link) Fa name2 with the attributes of the underlying object pointed at by Fa name1 . If the link is successful: the link count of the underlying object is incremented; Fa name1 and Fa name2 share equal access and rights to the underlying object.

If Fa name1 is removed, the file Fa name2 is not deleted and the link count of the underlying object is decremented.

The object pointed at by the Fa name1 argument must exist for the hard link to succeed and both Fa name1 and Fa name2 must be in the same file system. The Fa name1 argument may not be a directory.

The Fn linkat system call is equivalent to Fa link except in the case where either Fa name1 or Fa name2 or both are relative paths. In this case a relative path Fa name1 is interpreted relative to the directory associated with the file descriptor Fa fd1 instead of the current working directory and similarly for Fa name2 and the file descriptor Fa fd2 .

Values for Fa flag are constructed by a bitwise-inclusive OR of flags from the following list, defined in In fcntl.h :

AT_SYMLINK_FOLLOW: If Fa name1 names a symbolic link, a new link for the target of the symbolic link is created.

If Fn linkat is passed the special value AT_FDCWD in the Fa fd1 or Fa fd2 parameter, the current working directory is used for the respective Fa name argument. If both Fa fd1 and Fa fd2 have value AT_FDCWD the behavior is identical to a call to Fn link . Unless Fa flag contains the AT_SYMLINK_FOLLOW flag, if Fa name1 names a symbolic link, a new link is created for the symbolic link Fa name1 and not its target.

RETURN VALUES

Rv -std link

ERRORS

The Fn link system call will fail and no link will be created if:

Bq Er ENOTDIR: A component of either path prefix is not a directory.
Bq Er ENAMETOOLONG: A component of either pathname exceeded 255 characters, or entire length of either path name exceeded 1023 characters.
Bq Er ENOENT: A component of either path prefix does not exist.
Bq Er EOPNOTSUPP: The file system containing the file named by Fa name1 does not support links.
Bq Er EMLINK: The link count of the file named by Fa name1 would exceed 32767.
Bq Er EACCES: A component of either path prefix denies search permission.
Bq Er EACCES: The requested link requires writing in a directory with a mode that denies write permission.
Bq Er ELOOP: Too many symbolic links were encountered in translating one of the pathnames.
Bq Er ENOENT: The file named by Fa name1 does not exist.
Bq Er EEXIST: The link named by Fa name2 does exist.
Bq Er EPERM: The file named by Fa name1 is a directory.
Bq Er EPERM: The file named by Fa name1 has its immutable or append-only flag set, see the chflags(2) manual page for more information.
Bq Er EPERM: The parent directory of the file named by Fa name2 has its immutable flag set.
Bq Er EXDEV: The link named by Fa name2 and the file named by Fa name1 are on different file systems.
Bq Er 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.
Bq Er 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.
Bq Er EIO: An I/O error occurred while reading from or writing to the file system to make the directory entry.
Bq Er EROFS: The requested link requires writing in a directory on a read-only file system.
Bq Er EFAULT: One of the pathnames specified is outside the process's allocated address space.

In addition to the errors returned by the Fn link , the Fn linkat system call may fail if:

Bq Er EBADF: The Fa name1 or Fa name2 argument does not specify an absolute path and the Fa fd1 or Fa fd2 argument, respectively, is neither AT_FDCWD nor a valid file descriptor open for searching.
Bq Er EINVAL: The value of the Fa flag argument is not valid.
Bq Er ENOTDIR: The Fa name1 or Fa name2 argument is not an absolute path and Fa fd1 or Fa fd2 , respectively, is neither AT_FDCWD nor a file descriptor associated with a directory.

STANDARDS

The Fn link system call is expected to conform to St -p1003.1-90 . The Fn linkat system call follows The Open Group Extended API Set 2 specification.

HISTORY

The Fn link function appeared in AT&T System v7 . The Fn linkat system call appeared in Fx 8.0 .

The Fn link system call traditionally allows the super-user to link directories which corrupts the file system coherency. This implementation no longer permits it.