NFS, hung processes

[Jonathan I. Kamens]

Query: any reason why this wasn't asked in comp.protocols.nfs?

In article <24D1DF49.7A5 at marob.masa.com> samperi at marob.masa.com (Dominick
Samperi) writes:
>There seems to be no obvious way to deal with the problem of hung processes
>due to a dead NFS server. The recently posted 'cknfs' program might help
>somewhat, but it does not deal with the situation where a server dies after
>a user logs in. Furthermore, it appears that a process may still hang
>even if no reference is made to dead NFS paths. I don't know why...perhaps
>the crashed machine is flooding the network with garbage packets????
>
>Perhaps some experienced NFS users could comment on various tricks that they
>have used to deal with the "NFS hang problem"?

  Project Athena has well over 1,000 workstations, with over 10,000
user accounts, and every user gets his home directory over NFS.  There
are also a lot of third-party lockers that people use often that are
exported via NFS.  We therefore encounter this problem much more often
than we'd like.

  The most common way of referencing a dead NFS path even if you don't
realize you're doing it is if you have said path in your search path
and try to execute a program and/or start a new shell.  Both will
cause the search path to be scanned, and they could encounter the dead
path and hang on it.

  One solution, which is what we use, is not to hard mount anything
but the most important NFS filesystems.  We mount all user filesystems
soft with a five minute error timeout by default, so if a user's
fileserver goes down, processes will only try to access it for five
minutes.  Once the user gets his prompt back, he can carefully save
whatever work he is doing to a local hard disk or mail it to himself
to prevent it from being lost.

  The only filesystems we hard mount by default are the system
software packs, since if they go down there isn't much you can do with
the workstation anyway.

Jonathan Kamens			              USnail:
MIT Project Athena				432 S. Rose Blvd.
jik at Athena.MIT.EDU				Akron, OH  44320
Office: 617-253-4261			      Home: 216-869-6432