ugh.book

294 NFS

One of the reason that NFS silently corrupts files is that, by default, NFS is

delivered with UDP checksum error-detection systems turned off. Makes

sense, doesn’t it? After all, calculating checksums takes a long time, and

the net is usually reliable. At least, that was the state-of-the-art back in

1984 and 1985, when these decisions were made.

NFS is supposed to know the difference between files and directories.

Unfortunately, different versions of NFS interact with each other in strange

ways and, occasionally, produce inexplicable results.

Date: Tue, 15 Jan 91 14:38:00 EST

From: Judy Anderson <[email protected]>

To: UNIX-HATERS

Subject: Unix / NFS does it again...

boston-harbor% rmdir foo

rmdir: foo: Not a directory

boston-harbor% rm foo

rm: foo is a directory

Eek? How did I do this???

Thusly:

boston-harbor% mkdir foo

boston-harbor% cat > foo

I did get an error from cat that foo was a directory so it couldn’t out-

put. However, due to the magic of NFS, it had deleted the directory

and had created an empty file for my cat output.

Of course, if the directory has FILES in it, they go to never-never

land. Oops. This made my day so much more pleasant... Such a

well-designed computer system.

yduJ (Judy Anderson) [email protected]

'yduJ' rhymes with 'fudge'

Freeze Frame!

NFS frequently stops your computer dead in its tracks. This freezing hap-

pens under many different circumstances with many different versions of

NFS. Sometimes it happens because file systems are hard-mounted and a