NAME

       link, linkat — make a hard file link

LIBRARY

       Standard C Library (libc, -lc)

SYNOPSIS

       #include <unistd.h>

       int
       link(const char *name1, const char *name2);

       int
       linkat(int fd1, const char *name1, int fd2, const char *name2, int flag);

DESCRIPTION

       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>:

       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.

RETURN VALUES

       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 error.

ERRORS

       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 32767.

       [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.

       [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 information.

       [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 directory.

       [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.

       [EINTEGRITY]       Corrupted data was detected while reading from the file system.

       [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.

SEE ALSO

       chflags(2), readlink(2), symlink(2), unlink(2)

STANDARDS

       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.

HISTORY

       The link() function appeared in Version 1 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.

Debian                                           March 30, 2020                                          LINK(2)