Monday, June 23, 2008

Exim is a bit nuts

I'm using Nagios to monitor servers, but was having some trouble getting emails to exit the Ubuntu JeOS server that I had set up to run it under VMware. (Most of my stuff is Windows, and Nagios is a linux program). It turns out that a program called exim is used to send emails, and it's a bit crazy.

All attempts to send email to myself resulted in replies which contained the error:
all relevant MX records point to non-existent hosts
Thanks to this entry on the PkgExim4UserFAQ, I was able to get a clue

A probable cause for this might be that all MX records for the offending domain point to site local or link local IP addresses, which are ignored by the dnslookup router to protect from misconfigured external domains. The default configuration has relaxed checking for domains that the local system is configured to allow relaying to, so adding the offending domain to dc_relay_domains will most probably help. Please note that this entry might be necessary anyway to bypass relay control for the domains in question.

Please note that no domain on the public Internet should have MX records pointing to site local or link local IP addresses, so you might check your externally visible MX records.

If this doesn't help, try analyzing the output of exim -d -bt some.local.part@the.offending.domain.example

Well, I did the requisite test, to find this among the output

ignored host mail.xxxx.com [10.0.0.x]

Ignored host?? Clearly not the same as one that is non-existent. So... the first error was a lie.

All the relevant records pointed correctly to a very much alive and well host, but exim chose to ignore it because it was local.

In order to get around this, you have to follow the suggestion of Marc Haber and tell it that it is going to relay email for your local domain (which sounds like a very bad idea) in order to get it to work.

I don't know why they did it this way, but I'm posting this here to help others figure it out.

Monday, June 16, 2008

XP era ends?

Larry Dignan over at ZDnet asks:

XP era ends: Will Vista step up?

Larry assumes that Vista is inevitable, and that anyone who questions it is unpatriotic... er... just a complainer. He then goes on to the straw men:

If you’re a Vista complainer you have two options from here:

  • Move away from Windows completely (users try a new OS and developers jump ship).
  • Or shut up and go with Vista.
Now, the false choice here asserts that all non-Vista operating systems will suddenly and completely have no value once Microsoft, in their infinite wisdom says so.

There are a lot of reasons to avoid Vista like the plague. People went along with having pre-loaded Windows back when new versions were generally an UP-grade... but Vista breaks far too many things, and causes way too much grief. There is a lot of user hostility being build up over this, causing people to start searching for alternative platforms as an escape route.

Linux seems to be the platform of choice, be it on a Mac or a PC. We can all run XP under VMware if we need to run some application that can't get ported eventually to Linux. Microsoft is quite aware of the place they are putting everyone into, but really has no choice in the matter. They desperately want to keep their OS market share to help drive their Office cash cow, but know that this is ultimately a losing proposition. So they will keep the drama going, probably announcing some form of "extended support" to keep it alive for a while longer to prevent defection to Linux.

The XP era is ending, long live Linux.

Sunday, June 08, 2008

166437 and counting

I've managed to gather all of my photos from the last 11 years in one disk, and I've got 166,437 distinct Jpeg files, plus some movies in AVI and MPG, and a few NEF files. WOW

Friday, June 06, 2008

Mellon Collie


I got a nice spiffy new hard drive to gather all my photos together on... only to find out that I may have lost a few years worth due to inadequate backups... ugh, I'm feeling a bit of Melancholia.

My main task now is to fight through this, and try to recover what I can. Ugh!

Update: I have all of them in a lower resolution format... good enough for small prints... still working on getting the originals back.

Tuesday, June 03, 2008

Towards a new database model

Over the past few days I've been pondering the way databases get used, and I think I have a way to help make things better by shifting things around a bit. I'm going to dive right in to deep territory here...

The current crop of SQL type databases are all batch oriented. They just don't scale well because of this. We need to update the model from one of data that gets visited by the occasional query to one where the queries are always running and updating their results.

If you find yourself requerying a database without having changed the data yourself, you're wasting a huge amount of resources. You really only want to know what's changed, and it's silly to re-examine everything that isn't modified since the last run of the query.


Imagine a table in a database. If you recorded the initial state of the table, and all of the subsequent operations, you could perfectly replicate the state of the table.

If you then wrote code to implement this type of logic, it takes a lot less code to keep valid replicas. You would have a stream of changes instead of a set of facts that constantly needed to be reexamined.

If you ran a query against such a table, then ran the query against the stream of changes, you could have a running output that worked vastly more efficiently, since you only have to examine records that have changed.

I'm not a computer scientist, nor an engineer, but it seems to me that this model should be looked into a bit, and has some promise to save us all some time and effort.

Who knows, it might even save Twitter.

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