Help, I have a mission critical VPS runing Ubuntu 10.04 , which I am using for django. the web-app has been running fine for a month and then suddenly I can't write to the sqlite database anymore, getting an "disk i/o" error (no problems reading from it though). which from what I can tell is usually permission problem. Nothing worked so I tried reseting the permissions to 777 and owner to www-data allong on the directory it's in and all the files, still no luck. I then SU'd to the www-data user and ran echo "hi" > hi.txt followed by cat hi.txt, and it was blank. I ran ls to see if it had been created even, and it was there, it was just blank. I switched back to root and ran cat hi.txt, and it was still blank, so I ran echo "hi" > hi.txt again followed by cat hi.txt and it now said correctly "hi" back. I switched back to www-data to see if I could read it, and I could. www-data is the owner of hi.txt and permissions where 644 . What can I do? It seems like www-data suddenly can't write inside a file (it can however create them), but can only read no matter what the permissions or who owns it. Help!
Smells unpleasant. My first suspicion would be a filesystem problem with symptoms that screwy. Check dmesg for filesystem errors, perhaps take a maintenance to do a fsck to be sure.