> This might be a question out
> of ignorance, but is this a symbolic link (ln -s) or a hard link, and what
> is the difference anyway?
With a hard link, you have a separate directory entry to the identical
inode on the disk. The resulting link is *indistinguishable* from the
original file and will persist through a renaming of the original file.
In fact, if you delete the original file, the link will still point to
the real data. (An inode is not actually marked as "deleted" until all
references to it are deleted. With a hard link, you just have multiple
references to the same point on the disk.)
With a symbolic link, you have a separate directory entry pointing
to the *name* of the original file. Windows 95 added this type of
thing with a "Shortcut", and MacOS has an "alias". A symlink just
points to the filename. If the original file is renamed, moved,
or deleted, the link breaks.
Here is a real quick look at the difference. Note that I am using the
'-i' option to the ls command that shows the actual inodes on disk.
I have one file:
$ ls -li
total 16
1811630 drwxrwxr-x 2 dyork dyork 4096 Oct 25 12:29 ./
179521 drwxrwxrwt 40 root root 4096 Oct 25 12:28 ../
1811631 -rw-r--r-- 2 dyork dyork 1164 Oct 25 12:29 foo
I make the links:
$ ln foo hfoo
$ ln -s foo sfoo
$ ls -li
total 16
1811630 drwxrwxr-x 2 dyork dyork 4096 Oct 25 12:29 ./
179521 drwxrwxrwt 40 root root 4096 Oct 25 12:28 ../
1811631 -rw-r--r-- 2 dyork dyork 1164 Oct 25 12:29 foo
1811631 -rw-r--r-- 2 dyork dyork 1164 Oct 25 12:29 hfoo
1811632 lrwxrwxrwx 1 dyork dyork 3 Oct 25 12:29 sfoo -> foo
Note that the hard link shows the same size as the original as it *is*
the same thing as the original. They symlink shows a size of the number
of characters in the name it is linking to.
Move the original file. Hard link works. Symlink is broken.
$ mv foo foo2
$ ls -li
total 16
1811630 drwxrwxr-x 2 dyork dyork 4096 Oct 25 12:35 ./
179521 drwxrwxrwt 40 root root 4096 Oct 25 12:28 ../
1811631 -rw-r--r-- 2 dyork dyork 1164 Oct 25 12:29 foo2
1811631 -rw-r--r-- 2 dyork dyork 1164 Oct 25 12:29 hfoo
1811632 lrwxrwxrwx 1 dyork dyork 3 Oct 25 12:29 sfoo -> foo
Delete the original file. Hard link works. Symlink is broken.
$ rm foo2
$ ls -li
total 12
1811630 drwxrwxr-x 2 dyork dyork 4096 Oct 25 12:36 ./
179521 drwxrwxrwt 40 root root 4096 Oct 25 12:28 ../
1811631 -rw-r--r-- 1 dyork dyork 1164 Oct 25 12:29 hfoo
1811632 lrwxrwxrwx 1 dyork dyork 3 Oct 25 12:29 sfoo -> foo
Create a new file with the original *name*. Hard link points to the
*original* contents. Symlink now works, but points to the *new* contents
(which in this case is nothing).
$ touch foo
$ ls -li
total 12
1811630 drwxrwxr-x 2 dyork dyork 4096 Oct 25 12:36 ./
179521 drwxrwxrwt 40 root root 4096 Oct 25 12:28 ../
1811633 -rw-rw-r-- 1 dyork dyork 0 Oct 25 12:36 foo
1811631 -rw-r--r-- 1 dyork dyork 1164 Oct 25 12:29 hfoo
1811632 lrwxrwxrwx 1 dyork dyork 3 Oct 25 12:29 sfoo -> foo
$
You will find that things like init scripts (and most system admin
that I can think of) gets done with symlinks, as there is only
*one* definite copy of the contents. You also cannot do a hard link
from one partition to another, as they both need to point to the same
inode on the disk they are on... but you can do symlinks from anywhere
to anywhere.
Dan
--
Dan York, Director of Training, Network Server Solutions Group
Mitel Networks Corporation [EMAIL PROTECTED]
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