Re: ls -L [some symbolic linked file] not working
Re: ls -L [some symbolic linked file] not working
- Subject: Re: ls -L [some symbolic linked file] not working
- From: Mailing list subscriptions <email@hidden>
- Date: Wed, 20 Sep 2006 13:17:16 +0200
El 20/09/2006, a las 12:51, Steve Checkoway escribió:
I disagree. While both of those properties of links are true, I
wouldn't say that's the difference. As I'm sure you well know, a
hard link is just another link to the same inode with a different
path. I know that either HFS or OS X (I'm not sure which) has
issues with files that have at any point been hard linked whereas a
symbolic link is a different file which points to a path (as can be
read by readlink(2)). There is no difference between an original
link to a file and a hard link to the file. For all intents and
purposes, they are the same file. This is not true of a symlink.
Hard links as implemented in 10.0:
HFS+ lacks support in the volume format for hard links, a standard
feature of UFS. Initially, the attempted creation of a link to a
file would yield a "not supported" error. We had discussed some
"80%" solutions, such as creating symbolic links instead, but the
semantics of symbolic links are significantly different. For
troubleshooting reasons it is preferable to fail at link creation
time than at some later time due to problems related to these
semantic differences. The problem is that there is a significant
amount of software which breaks if hard link creation fails, and
some of that software needs to be redesigned if hard links cannot
be used. In order to accommodate this software, we now emulate hard
links by creating a "kernel-level" symbolic link which is visible
only to and interpreted by the HFS+ file system. This was necessary
due to the lack of support in the volume format. The resulting
behavior is very similar to that of hard links when viewed from
above the kernel, though they are relatively inefficient in
comparison.
http://www.wsanchez.net/papers/USENIX_2000/
Information on hard links (to directories!) in Leopard:
Apple added traditional hard links (that is, hard links to files)
to HFS+ back before Mac OS X 10.0 was released. In Leopard, HFS+
supports hard links to directories as well—an ability wholly alien
to any other Unix-like operating system that I can think of. This
is how Time Machine builds its sparse trees. The very first backup
is a full copy. All subsequent backups contain hard links to the
unchanged portions of the previous backup.
http://arstechnica.com/staff/fatbits.ars/2006/8/15/4995
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