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SubjectRe: Symlink indirection
On Fri, 13 Dec 2002, Amos Waterland wrote:

> I think that you and Richard are dicussing a slightly different issue
> than the original poster asked about. The original question was:
>
> On Fri, 13 Dec 2002, Andrew Walrond wrote:
> > Is the number of allowed levels of symlink indirection (if that is the
> > right phrase; I mean symlink -> symlink -> ... -> file) dependant on the
> > kernel, or libc ? Where is it defined, and can it be changed?
>
> To which Richard replied:
>
> > Since a symlink is just a file containing a name, the resulting path
> > length is simply the maximum path length that user-space tools allow.
> > This should be defined as "PATH_MAX". Posix defines this as 255
> > characters but I think posix requires that this be the minimum and all
> > file-name handling buffers must be at least PATH_MAX in length.
> >
> > A hard link is just another directory-entry for the same file. This,
> > therefore follows the same rules. There must be enough space on the
> > device to contain the number of directory entries, as well as enough
> > buffer length in the tools necessary to manipulate these "nested"
> > directories, which are not really "nested" at all.
>
> But Richard is not actually completely correct. There is a limit of 5
> levels of symlink indirection in vanilla 2.4 series Linux kernels.
>
> % touch 0
> % for i in `seq 1 10`; do ln -s `ls | sort | tail -1` $i; done
> % ls
> 0 1 10 2 3 4 5 6 7 8 9
> % cat 5
> % cat 6
> cat: 6: Too many levels of symbolic links
> % strace cat 6 2>&1 | grep 'open("6",'
> open("6", O_RDONLY|O_LARGEFILE) = -1 ELOOP (Too many levels of symbolic links)
>
> This has been discussed by Al Viro et al. many times on lkml. I believe
> that it is not a user-space or POSIX issue, but rather a kernel issue.
> Thanks.
>
> Amos Waterland
>

Yep. I thought the original poster was talking about following
the links, i.e., "indirection", rather than creating links which
is "definition".

So, the kernel does set a limit on the number of symlinks of the form,

ln -s a b ; ln -s b c ; ln -s c d ; ln -s d e ; # etc.


Cheers,
Dick Johnson
Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
Why is the government concerned about the lunatic fringe? Think about it.


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