"Troy Rollo" <t...@parrycarroll.com.au> writes: > You can hard link a directory (historically done as root using /etc/link or > /sbin/link rather than /usr/bin/ln or /bin/ln).
On which file system, without causing it serious errors? I can't say categorically that nothing allows it, but it is considered to be a serious violation of the semantics of the system by ... well, most things. Certainly all the common file system drivers in Linux, as well as by the core VFS; see http://lxr.linux.no/linux+v2.6.34/fs/namei.c#L2423 for vfs_link: 2445 if (S_ISDIR(inode->i_mode)) 2446 return -EPERM; So, you could, but only if you go back far enough that unlink('/') worked, along with those other nasty ways to break the file system and all. :) > Doing so traditionally requires (1) root; and (2) a direct call to the > "link" system call (which is what the old /etc/link and /sbin/link did). ...while you used to be able to break things as root, on some platforms, it wasn't ever considered a healthy thing to do — at least, to the best of my knowledge on the topic. > However if this is indeed what has been done, then I can speculate as to > what might have happened. I seem to recall that the Linux kernel caches the > file system hierarchy Nope. That isn't even close to accurate; the way data is cached varies wildly between different systems, but it isn't especially hierarchical; file data is usually in the page cache indexed by inode. > in which case there is might be a chance that the kernel cached hierarchy > does not reflect what is on disk. Well, if the file system was fundamentally broken it would certainly break caching, but usually in vastly more nasty ways than this. > Hard linking directories is a sufficiently unusual thing to do that it is > possible such a cache was never tested against it. Actually, it is impossible in anything resembling a recent Linux kernel as noted, so this categorically *cannot* be the cause of the issue. Daniel -- ✣ Daniel Pittman ✉ dan...@rimspace.net ☎ +61 401 155 707 ♽ made with 100 percent post-consumer electrons -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
