Upgrading the IBM T41 to Fedora Core 5, debugging

As noted in my last post, I had the very odd problem that Google mail would not work after the upgrade. I was really confused what about the upgrade could have caused this, but by the end of the day I was starting to have my suspicions. I did not have a great deal of time to work the problem during the day in any case, having that day job and all, so after hours I fired up WireShark (formerly Ethereal) and traced the failure. I then pondered the trace for a bit, and googled up a few more things.

At the same time, a good friend and reader of “Adventures” wrote me to say he had two FC5 virtual machines on his home server and neither had the problem I was describing.

I went home, fired up my FC5 guest on the Mac, updated it to current, and tested it: Google mail was fine there.

The help files over at Google kept telling me that this kind of problem only happens when my local disk cache is corrupt. But it turns out there is another kind of cache that can be corrupt and cause it: A network cache. I found a reference in the trace that said “Not Modified”, coming out of the networking caching appliance. Then a time-out from Google forcing a reset, over and over.

To bypass this, I went it to Google Mail with https:// rather than http://. And now it works fine.

In retrospect, this is probably a best practice anyway. Gmail flips to https for userid/password stuff but otherwise would use clear text transport. Using https:// to log in, my whole session will be SSL, and snoopy folks out there on the wire won't be able to so easily read my private family recipes for lefse.