Not programming... not really computers...
 

Does anyone know why I cannot create a hard link to a directory with 'ln' on my linux box? The man page reads:

-d, -F, --directory
hard link directories (super-user only)

So su'ed to root, I shouldn't be getting this:

$ ln -d mail myMail
ln: creating hard link `myMail' to `mail': Operation not permitted

You mean, # ln -d mail myMail? =P
Hmm I'm not sure, is mail a symbolic link? (I don't actually know whether you're allowed to make hard links to symlinks, just a random guess.)

edit: don't think that's it

I assume they're on the same filesystem

what if you tried

$ ln -d mail/ myMail/ ?

or try just

$ ln mail myMail
(or)
$ ln mail/ myMail/


Do any of those combos work for you? I'm thinking the first and second would, but not sure.

Do you really want a hard link to a directory? Directory hard links are hard to make for a reason. I'd generally advise making a soft link unless you have a very specific reason to make a hard link.

Since you have already had answers about the hard link, may I ask the reasoning you are going against a symlink here?

I find that symlinking directories are often much easier.

I'm not doing this for any particular reason, just out of curiousity really. I generally don't like being told I can do something (in the man page) and then trying it and have it not work.

Yes, they are both on the same FS, actually they would be residing in the same directory if you take my command line exactly.

No, the original directory is not a symlink.

I guess it's more trying to figure out why this wouldn't work, or wouldn't be advisable. A directory is just a file with another bit set, is it not? Still held in an inode. Why is it OK to have a file that's hard linked, but not a directory then?

Edit: results of the above:
[root@mybox ~]# ln -d mail/ myMail/
ln: creating hard link `myMail/' to `mail/': No such file or directory

[root@mybox ~]# ln mail mymail
ln: `mail': hard link not allowed for directory

[root@mybox ~]# ln mail/ myMail/
ln: `mail/': hard link not allowed for directory

http://c2.com/cgi/wiki?HardLink

This link has information you might be interested in.

Hey, it wanted to work that time!

One mistake I frequently make with ln is that I give the args in the wrong order. I forget that it's "from" and "to" like cp, I for some reason thing the syntax ought to be more like "link this new thing to that old thing". Could that have bitten you?

Ahhh.. reversed args.. that makes sense.

Read firebirdta's link.

Making directory symlinks can break some filesystems. There is a reason only root can do it. Unless you have a very good reason to do it, understand precicely what the implications are on your particular filesystem, and are sufficiently skilled to do debugging on filesystem internal data structures, do not do it.

So, I'm a bit paranoid.

No, the args are definatly in the right order. That wiki link makes sense, especially:

That makes sense why even as root I cannot do it.

quick question....what happens if you try full path names to the directories? I've had that sort of thing come up as well...especially with that command that gave the "no such file or directory" jazz

Doesn't seem to matter, take the three examples above, with full paths, they return the same error messages.