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List:       linux-net
Subject:    Re: NFS/root problem
From:       miquels () drinkel ! cistron ! nl (Miquel van Smoorenburg)
Date:       1996-09-28 0:28:12
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In article <1.5.4.16.19960927002516.5fdf8430@mailhost.3wave.com>,
Mark Lane  <mlane@3wave.com> wrote:
>Hi everyone.
>        I have a Debian Linux 2.0.6 box which is NFS-mounting /var/spool/mail 
>and /home from a Slakware Linux 1.2.8 box.  The 1.2.8 file system is exported 
>using default values, and UID's/GID's are shared between both systems.  

Oh-oh. File locking doesn't work over NFS, so if someone is updating
his mailbox while mail is coming in.. bye bye mailbox.

This is because Linux currently doesn't have a "lockd", a file lock deamon.
Even commercial systems that do have it don't always get it right.
Dot-locking (locking the mailbox with a user.lock file) is supposed to
overcome this, but all mail programs (except procmail) use O_EXCL to
do dotlocking and guess what.. that also doesn't work over NFS (ARRRGH!)
I've recently posted a kernel patch on linux-kernel to fix this, but
it won't be in 2.0.x. It'll be in 2.1.x probably, oh well.. Anyway
this doesn't work on any other system as well currently.

>The 2.0.6 box is mounting the file system using default settings.  
>        The root account on the 2.0.6 client box cannot access NFS-mounted
>files for read or write.  I have read the man pages for exports, nfsd, mountd, 
>and mount on both boxes, along with the NFS-root mini-howto (just in 
>case...), but cannot find anything to indicate what's wrong.

In /etc/exports:

/var/spool/mail		otherbox(rw,no_root_squash)

See "man exports".

But I would _strongly_ suggest you do _not_ share /var/spool/mail over
NFS. It's just asking for trouble..

Mike.
-- 
+   Miquel van Smoorenburg   + Cistron Internet Services +  Living is a     |
|  miquels@cistron.nl (SP6)  | Independent Dutch ISP     |   horizontal     |
+ miquels@drinkel.cistron.nl + http://www.cistron.nl/    +      fall        +

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