From: Wade Hampton <wade.hampton@nsc1.net>
Subject: df hangs on down nfs server mounted with hard,intr, can't kill
Date: Tue, 09 Mar 2004 14:33:01 -0500
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[I posted this to the Fedora list yesterday.]

I have a Fedora server with kernel 2.4.22-1-2163 SMP mounting a
remote solaris server (hence choice of options):

  rsize=32768,ro,hard,intr,tcp,nfsvers=3

When the remote is down or disconnected, a "df" hangs (as expected),
but I can't kill it, even as root or with kill -9.  The docs for mount 
indicate
that the INTR option should allow for killing apps mounted with HARD.
Is this a bug (glibc, 2.4 kernel, NFS, or Fedora's kernel)?

I also coded a test program that calls statvfs(2) and it hangs on
the statvfs(2) call when run against a down NFS server.  It too
can't be interrupted or killed.

My questions are:

1)  Is there a safe and reliable means to check for a down NFS server
    (e.g., is showmount -e <server> safe enough?)

2)  Is the non-interruptable operation (even with INTR option)
    a bug or feature?

3)  Is there a simple kernel call, /proc entry, or similar that can
   be used to reliably check for free/used disk space and for a down
   host, without hanging my application?
  
       A showmount -e followed by a statvfs() might work, but
       there is the possibility of losing the host between the two
       calls, resulting in an application hang.

4)  Is there a perl module to accomplish this?

This would be very useful for network monitoring, e.g., when the
server goes down and stays down for >1 minute, generate an SNMP
trap and write to a log file.  It would be good if you can't put an SNMP
agent on the server, but only on the client.  It is also useful for writing
a highly reliable client application.

As I have no control over the remote system, when it went down,
I had to do a hard reboot of my Linux box to stop the hung apps.  This
is a Windows solution, not a Linux solution....
 
Note, I found this when writing some scripts for MRTG to check
the disk utilization of partitions.  My df's hung so I didn't even get
the proper values for my local partitions.  After a few days, I had
LOTS of hung MRTG apps and had to reboot (this test server is
down for a week or two).

Thanks
-- 
Wade Hampton


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