Xaprb

Newer Linux kernels have per-process I/O accounting and you can use the iotop tool to find out what’s performing I/O, but in many cases I’m trying to find the source of an I/O problem in an older kernel. I found sort of a hack-ish way to do that today, while trying to figure out why a system was basically unresponsive.

I found a post on Stack Overflow that showed a way you can get per process I/O statistics from the kernel even in older kernels. I adapted this to my needs, and wrote a little script.

Here’s how you use it. First, get it:

wget http://aspersa.googlecode.com/svn/trunk/iodump

Then turn on kernel messages about I/O:

echo 1 > /proc/sys/vm/block_dump

This makes the kernel start writing messages about every I/O operation that takes place. Now all you have to do is get those messages and feed them into my script:

while true; do sleep 1; dmesg -c; done | perl iodump

Wait a little while, then cancel the script. The results should look something like the following:

root@kanga:~# while true; do sleep 1; dmesg -c; done | perl iodump
^C# Caught SIGINT.
TASK                   PID      TOTAL       READ      WRITE      DIRTY DEVICES
firefox               4450       4538        251       4287          0 sda4, sda3
kjournald             2100        551          0        551          0 sda4
firefox              28452        185        185          0          0 sda4
kjournald              782         59          0         59          0 sda3
pdflush                 31         30          0         30          0 sda4, sda3
syslogd               2485          2          0          2          0 sda3
firefox              28414          2          2          0          0 sda4, sda3
firefox              28413          1          1          0          0 sda4
firefox              28410          1          1          0          0 sda4
firefox              28307          1          1          0          0 sda4
firefox              28451          1          1          0          0 sda4

I deliberately generated a bunch of I/O by deleting my Firefox history and cache.

Got any better ideas, warnings, etc? Post them in the comments.

My brother sent me these thoughts, slightly edited:

Recently I looked at the [Wikipedia] Linux page. To my surprise it’s not about the kernel Linux, it’s about the “OS”. I looked at discussion and it appears that by general consensus the term Linux applies to the unix like operating system, and so it is correct for Wikipedia to follow that consensus. So, instead of providing information, they are deliberately misleading folks… Often what the majority does is wrong because the majority of people are not the experts. By definition, the experts are a minority.

You’d expect a higher standard from Wikipedia, wouldn’t you? Wouldn’t you? Aw, come on, surely you don’t mean to imply that Wikipedia is a place where things become true because most people say so, do you?

Consensus, when used in this way, is nothing other than mind-rot for the masses, group-think at its worst. There is a valid use of the word when it applies to decision-making. But this isn’t about decision-making, it’s about out-voting or out-discussing.

What’s interesting to me is that I heard a radio interview with Wikipedia’s founder Jimmy Wales, and he was extremely careful to say GNU/Linux when discussing the operating system that runs the website.

Saying that Linux is an operating system has not, does not, and never will make it true any more than saying that a steering wheel is a car makes it so.

One of the minor things I’ve noticed when I use Thunderbird on my IMAP accounts is that it doesn’t download IMAP messages until I click on them. Then I have to wait until I can see the message. I have heard that this is supposed to be fixed in Thunderbird 3, and I tried it but a lot of the extensions I need aren’t compatible with it.

Today I finally tried to search and find out more about the problem. Turns out I’m not alone — others have noticed that the setting to download message bodies for offline use doesn’t do what it’s supposed to.

Fortunately, there’s an extension for this. It’s called Sync On Arrival. So far, it’s working like a charm. The only thing I had to do was edit the install.rdf to increase the version number. It’s compatible with Thunderbird 2, even though it says it’s not.

Edit: see the comments for a way to do this with configuration alone, rather than an extension.