Re: Mounted volume, different permissions

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Date: Thu, 25 Nov 2004 11:15:54 +0300

"ohaya" <ohaya@cox.net> wrote in message news:41A54FEB.42EFEB68@cox.net...
> Hi,
>
> I was working on installing Oracle onto a Solaris 9 system today, and
> ran into a very strange (to me) problem.
>
> What happened was that we originally had created a directory called
> "apps" under "/" on the hard drive and installed some of the Oracle
> software. Then, we decided that the "/" filesystem was too small for
> some other stuff we were going to be installing, so we uninstalled the
> Oracle software, and, using Veritas Volume manager, we created a 30GB
> volume.
>
> We then mounted the Veritas volume to "/apps", and proceeded to try to
> re-install the Oracle software, but we ran into problems. I struggled
> with this for awhile, then found that I was getting a "getcwd:
> permission denied" during the installation, but everything looked ok
> permission-wise when I checked using "ls -al / |grep apps".
>
> This happened even when I chmod'ed /apps and all the directories under
> that to 777 (I got desparate :)).
>
> I kind of puzzled over this for awhile, and did some searching, and
> found some posts indicating that 'sometimes', the permissions of the
> mount point can cause problems.
>
> I eventually ended up unmounting the Veritas volume, chmod'ed the
> "/apps" directory, then re-mounted the Veritas volume. After that, I
> tried the Oracle installation, and everything went fine.
>
>
> I guess that I'm happy that I was able to get around this problem (many,
> many hours), but I still am wondering about what exactly the problem
> was.
>
> I'm worried that I don't understand the problem exactly, and that it may
> come up again later.
>
>
> Can someone here explain this?
>
> What exactly is going on between the permissions of the underlying mount
> point vs. the permissions after the Veritas volume was mounted, i.e.,
> what are the "rules"?
>

I saw this already (not under Solaris). What apparently happens is
following - when you have to cd back up out of mounted filesystem the kernel
must first find the inode for mount point (in your case for /apps on root).
And it may happen that kernel is using the same rules for checking
permissions as for "normal" files - if you do not have permissions for the
_mount_point_ itself you simply cannot do "cd .." out of mounted filesystem.

getcwd just executes "cd ..; cd ..; ..." until it hits root that is why it
complaints.

I am rather surprised Solaris have this as well. But it seems to be common
to SVR4 derivatives.

> For example, should we always chmod the mount point to the desired
> permissions before mounting a Veritas volume?
>

it has nothing to do with Veritas. Consider:

bor@itspw1% ll /tmp/x
-rw-r--r-- 1 bor sinix 108462080 Nov 15 18:07 /tmp/x
bor@itspw1% sudo mount -r -F ufs /dev/lofi/1 /tmp/x
bor@itspw1% ll /tmp/x
total 72
drwxr-xr-x 2 root sys 512 Dec 18 2001 a/
lrwxrwxrwx 1 root other 9 Dec 19 2001 bin -> ./usr/bin/
...
bor@itspw1% cd /tmp/x
bor@itspw1% /bin/pwd
pwd: cannot determine current directory!

but

bor@itspw1% sudo -s
root@itspw1# cd /tmp/x
root@itspw1# /bin/pwd
/tmp/x

So yes, having at least 755 for *mount point* itself is almost a must.

regards

=arvi=

> Thanks,
> Jim

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