SUMMARY: When MAIL server is down all machines suffer..

From: Ricardo Marek (
Date: Sun Mar 15 1992 - 09:46:12 CST

A short resume of the original posting:

|> In our site, with 20 hosts, we have setup a mail-server, where all
|> machines mount /var/spool/mail, so the mailbox is in common for everybody.
|> Mail works realy nice...
|> BUT, When for other reasons the MAIL server is down, all machines suffer.
|> Then the response is very slow in those machines (even few minutes till you
|> get response from shell (csh or tcsh)), all this happens even if
|> /var/spool/mail is the only NFS mounted directory.
|> Here is the escenario:
|> 1) at the MAIL SERVER:(Called ariadna)
|> - /etc/exports:
|> ...
|> /var/spool/mail
|> ...
|> 2) At the suffering machines:
|> - /etc/fstab:
|> ...
|> ariadna:/var/spool/mail /var/spool/mail nfs soft,rw,bg,noquota 0 0
|> ...

The answers:

1) If you don't add the `noquota' to the /etc/fstab on the client side, you
   will get a very slow response, (When the NFS server is down), specially
   during the `login' time, that is, because the machine is trying to check
   Also you may work-around by linking the `quota check' program to /bin/true.

2) Other reason is that the shell, checks the mailbox (/var/spool/mail/$USER)
   each time you go back to command mode. This can be fixed by setting or
   changing some environment variables. (biff, mail, MAIL, MAILPATH, MAILCHECK)
   you may do a setenv MAIL to /dev/null, (or unnseting the mail variable),
   and in place, try using a kind of daemon that checks for in-comming mail..
   (like xbiff in X-windows)... so if the daemon hangs, who cares?..
   This is nice handled by mailtool(1).

3) If you know that the mail-server will be down, you may do some changes
   to prevent other machines do behave slow, by moving the mailhost to other
   To be ready for this, you need:
   - Create an alias for the mailhost in the NIS maps:

     From: To:
     .... .... vivaldi vivaldi mailhost ariadna mailhost ariadna
     .... ....

   - Move /var/spool/mail in the mail-server to /var/spool/mail.dir
   - Create a symbolic link from /var/spool/mail -> /var/spool/mail.dir
   - In the /etc/fstab file of each client that mounts /var/spool/mail:
     mailhost:/var/spool/mail /var/spool/mail nfs rw,bg,noquota 0 0
     This mounts mailhost:/var/spool/mail to /var/spool/mail.dir,
     then, if the server goes down, you can at least scramble to change
     the symbolic links, so that they do NOT refer to the hung NFS
     mount /var/spool/mail.dir
   - Check the `R' option in the /etc/ file, must be:
     If you change this, don't forget to re-build the /etc/sendmail.fc file!!

   (Assuming NIS, and the Master NIS server is not the mailhost machine!!)
   So yo use the NIS maps to change the location of the mail-server
   (This is the way I have procceded!! Ugly but works)

4) Some told me to reduce the `timeout' option, (in the /etc/fstab file),
   the default is 7 (tenths of sec.) and the reentry to 1.. but it caused
   /var/spool/mail mounting point to timeout each time, when the the
   mail-server (or the network) is overloaded..

5) We still use `soft' option (in the /etc/fstab file), because with `hard'
   NFS mounts, the machine gets stuck. (We know that with soft-links we may
   loose some info..)

I didn't want to summarize till the results were applied on our site.

I would like to thanks to: (In no special order..) (J. Anthony Fitzgerald) (Rob McCool) (Chris Siebenmann) (Wolfgang S. Rupprecht)!jones (Bill Jones) (Michael Rothstein)
     scott@netcom (Scott Corcoran) (Larry W. Virden) (Michael J Shon)

I appologise for all those I may have forgotten, or their replies got after
this posting.

--- Ricky Marek

Ricky Marek (System Manager)
Fibronics Ltd., Matam Industrial Park, Haifa 31905, ISRAEL
phones: +972-4-313690            Fax: +972-4-550550
e-mail:   or  ricky@fibronics.UUCP

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