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Full Discussion: links: (soft, hard? symbolic??) inode
Top Forums UNIX for Dummies Questions & Answers links: (soft, hard? symbolic??) inode Post 20925 by hugo_perez on Tuesday 7th of May 2002 05:06:32 PM
Old 05-07-2002
You have an explanation about hard links and soft links wiyh directories.

An explanation with files could be:

A file is referenced in the system by a i-node number, when you create a
file, the OS assign an i-node number to the file_name.
example:

a- create a file "pp"
echo "hard_soft_link_inode?" >> pp

b- list the file
ls -l pp
-rw-r--r-- 1 root system 22 May 07 18:39 pp
The number 1 is the number of hard links that the file has.

c- view the i-node number of pp assigned by the system:
ls -i pp
24 pp
the 24 number is the i-node number


d- when you make a hard link, the count of i-nodes of the file
is increased by 1 (and when you unlink the the hard link the number
is decreased by 1):

ln pp hard_link_to_pp
ln pp hard_link2_to_pp
ls -l pp
-rw-r--r-- 3 root system 22 May 07 18:39 pp

ls -i hard_link_to_pp
24 hard_link_to_pp

ls -i hard_link2_to_pp
24 hard_link_to_pp


if you remove the original file (you can access the file content by the
hard link)
rm pp

cat hard_link_to_pp
hard_soft_link_inode?

when you use the unlink command the i-node count decrease by 1:
unlink hard_link_to_pp
ls -l hard_link2_to_pp
-rw-r--r-- 1 root system 22 May 07 18:39 hard_link2_to_pp

if you unlink/rm again you lost the file.

Note: I prefer to use the unlink command over a hard link over the rm command.


The soft link is a pointer that could be point to nothing, to a file in the
same FS, or to a file in other FS (recommended use). To create a soft link
you need to use the "-s" flag of the "ln command".

A common use of hard links is some scripts in the rcX.d (X=1,2,3,S) that
are associated to files in the init.d directory. Use the "ls -i" in rc3.d and in the
init.d directories.

Good luck with your test, and sorry with my poor english.
 

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LEARN ABOUT HPUX

symlink

symlink(2)							System Calls Manual							symlink(2)

NAME

       symlink - make symbolic link to a file

SYNOPSIS

DESCRIPTION

       The function creates a symbolic link. Its name is the pathname pointed to by path2, which must be a pathname that does not name an existing
       file or symbolic link. The contents of the symbolic link are the string pointed to by path1.

RETURN VALUE

       Upon successful completion, returns 0. Otherwise, it returns -1 and sets to indicate the error.

ERRORS

       If fails, is set to one of the following values:

	      [EACCES]		       Write permission is denied in the directory where the symbolic link is being created, or search	permission
				       is denied for a component of the path prefix of path2.

	      [EEXIST]		       The path2 argument names an existing file or symbolic link.

	      [EFAULT]		       path1  or path2 points outside the process's allocated address space.  The reliable detection of this error
				       is implementation-dependent.

	      [EIO]		       An I/O error occurred while reading from path1, making the directory entry for path2, allocating the  inode
				       for path2, or writing out the link contents of path2.

	      [ELOOP]		       Too many symbolic links were encountered in resolving path2.

	      [ENAMETOOLONG]	       The length of the path2 argument exceeds or pathname resolution of a symbolic link produced an intermediate
				       result that exceeds or a pathname component is longer than

	      [ENOENT]		       A component of path2 does not name an existing file or path2 is an empty string.

	      [ENOSPC]		       The directory in which the entry for the new symbolic link is being placed cannot be  extended  because	no
				       space  is  left	on  the  file  system containing the directory, or the new symbolic link cannot be created
				       because no space is left on the file system which will contain the link, or the file system is out of file-
				       allocation resources.

	      [ENOTDIR] 	       A component of the path prefix of path2 is not a directory.

	      [EROFS]		       The new symbolic link would reside on a read-only file system.

APPLICATION USAGE

       Like  a hard link, a symbolic link allows a file  to have multiple logical names. The presence of a hard link guarantees the existence of a
       file, even after the original name has been removed. A symbolic link provides no such assurance; in fact, the file named by the path1 argu-
       ment need not exist when the link is created. A symbolic link can cross	file  system boundaries.

       Normal permission checks are made on each component of the symbolic link pathname during its resolution.

AUTHOR

       was developed by the University of California, Berkeley.

SEE ALSO

       cp(1), chown(2), link(2), lstat(2), open(2), readlink(2), unlink(2), symlink(4), <unistd.h>.

STANDARDS CONFORMANCE

CHANGE HISTORY

       First released in Issue 4, Version 2.

																	symlink(2)
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