Not File System Specific? (Not Quite) 293 Date: Fri, 5 Jan 90 14:01:05 EST From: curt@ai.mit.edu (Curtis Fennell)3 Subject: Re: NFS Problems To: all-ai@ai.mit.edu As most of you know, we have been having problems with NFS because of a bug in the operating system on the Suns. This bug makes it appear that NFS mounted files have been trashed, when, in fact, they are OK. We have taken the recommended steps to correct this problem, but until Sun gets us a fix, it will reoccur occasionally. The symptoms of this problem are: When you go to log in or to access a file, it looks as though the file is garbage or is a completely different file. It may also affect your .login file(s) so that when you log in, you see a different prompt or get an error message to the effect that you have no login files/ directory. This is because the system has loaded an incorrect file pointer across the net. Your original file probably is still OK, but it looks bad. If this happens to you, the first thing to do is to check the file on the server to see if is OK on the server. You can do this by logging directly into the server that your files are on and looking at the files. If you discover that your files are trashed locally, but not on the server, all you have to do is to log out locally and try again. Things should be OK after you’ve logged in again. DO NOT try to remove or erase the trashed files locally. You may accidentally trash the good files on the server. REMEMBER, this problem only makes it appear as if your files have been trashed it does not actually trash your files. We should have a fix soon in the meantime, try the steps I’ve recom- mended. If these things don’t work or if you have some questions, feel free to ask me for help anytime. —Curt 3Forwarded to UNIX-HATERS by David Chapman.

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 yduj@lucid.com 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) yduJ@lucid.com '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