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From: blymn@awadi.com.au (Brett Lymn)
Newsgroups: comp.os.386bsd.questions
Subject: Re: pwd problem with NFS
Date: 05 Sep 1994 06:55:47 GMT
Organization: AWA Defence Industries
Lines: 55
Message-ID: <BLYMN.94Sep5162547@mallee.awadi.com.au>
References: <33lntr$2ea@ale.dyas.leitch.com> <BLYMN.94Aug29125622@mallee.awadi.com.au>
<34akl9$8pj@ale.dyas.leitch.com>
NNTP-Posting-Host: mallee.awadi.com.au
In-reply-to: dchapes@dyas.leitch.com's message of 3 Sep 1994 16:00:41 -0400
>>>>> "Dave" == Dave Chapeskie <dchapes@dyas.leitch.com> writes:
In article <34akl9$8pj@ale.dyas.leitch.com> dchapes@dyas.leitch.com (Dave Chapeskie) writes:
Dave> In article <BLYMN.94Aug29125622@mallee.awadi.com.au>, Brett
Dave> Lymn <blymn@awadi.com.au> wrote:
>> No you have not checked all the permissions ;-) Unmount the nfs
>> mounted file systems and check the permissions on the
>> underlying mountpoints, if they are not read-execute for
>> everyone then you will get the strange messages you have been
>> seeing.
Dave> Ah Ah! It works okay now. But why does this happen?
Dave> Shouldn't either ls report the permissions on the underlying
Dave> mount point or shouldn't those permissions be ignored in
Dave> favor of the permissions on the mounted directory? It's
Dave> seems stupid and confusing to be using one set of
Dave> permissions while displaying another.
At first I was going to just shrug my shoulders and say "I dunno" but
after a bit of thought I think I have a theory (It's all mine!!!).
The theory goes that though we are used to thinking that a file system
"covers up" the underlying mount point. This cannot work for some
things. Consider the concept of "..", from the file system point of
view there is no ".." because it is the top of the tree. When that
file system gets mounted under another one then I suppose some magic
is done to point ".." of the mounted file system to the correct i-node
of the mount point so that when you do something like "cd .." it works
properly. Otherwise you would have the weird situation of doing a "cd
.." from the mounted file system and staying where you are - just like
you do in /.
Now if the permissions of the mount point are such that
you cannot read them then you cannot work out what you parent
directory is hence the message from ls *but* the permissions you see
for the mount point when something is mounted are those for "." of the
mounted file system *not* the mount point. Getting everything to work
so that you could see the underlying mount permissions without
breaking the concept of just having something that looks like one big
file system (anyone for VMS style sys$dsk0:[usr.blymn]? .... I thought
not ;-) would be - ummmm - challenging.
Managing disk storage on a unix system is made a lot easier by the
fact you can do things like "hmmmm /var is filling up / a lot - I'll
wack another disk on and mount it under /var to fix that"
Dave> I wonder how many
Dave> people get burned on this one.
*Lots* I am on a Sun mailing list and see this problem turn up quite
regularly.
--
Brett Lymn