Shallow Thoughts : : Dec

Akkana's Musings on Open Source Computing and Technology, Science, and Nature.

Sun, 23 Dec 2007

Gutsy's persistent net rules don't persist

I use wireless so seldom that it seems like each time I need it, it's a brand new adventure finding out what has changed since the last time to make it break in a new and exciting way.

This week's wi-fi adventure involved Ubuntu's current "Gutsy Gibbon" release and my prism54 wireless card. I booted the machine, switched to the right (a href="">network scheme, inserted the card, and ... no lights. ifconfig -a showed the card on eth1 rather than eth0.

After some fiddling, I ejected the card and re-inserted it; now ifconfig -a showed it on eth2. Each time I inserted it, the number incremented by one.

Ah, that's something I remembered from Debian Etch -- a problem with the udev "persistent net rules" file in /etc/udev.

Sure enough, /etc/udev/70-persistent-net.rules had two entries for the card, one on eth1 and the other on eth2. Ejecting and re-inserting added another one for eth3. Since my network scheme is set up to apply to eth0, this obviously wouldn't work.

A comment in that file says it's generated from 75-persistent-net-generator.rules. But unfortunately, the rules uesd by that file are undocumented and opaque -- I've never been able to figure out how to make a change in its behavior. I fiddled around for a bit, then gave up and chose the brute force solution:

And that worked fine. Without 75-persistent-net-generator.rules getting in the way, the name seen in 70-persistent-net.rules works fine and I'm able to use the network.

The weird thing about this is that I've been using Gutsy with my wired network card (a 3com) for at least a month now without this problem showing up. For some reason, the persistent net generator doesn't work for the Prism54 card though it works fine for the 3com. A scan of the Ubuntu bug repository reveals lots of other people hitting similar problems on an assortment of wireless cards; bug 153727 is a fairly typical report, but the older bug 31502 (marked as fixed) points to a likely reason this is apparently so common on wireless cards -- apparently some of them report the wrong MAC address before the firmware is loaded.

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[ 19:02 Dec 23, 2007    More linux | permalink to this entry | ]

Thu, 20 Dec 2007

Smart Wrapping with Greedy and Non-Greedy Regular Expressions

I had a chance to spend a day at the AGU conference last week. The American Geophysical Union is a fabulous conference -- something like 14,000 different talks over the course of the week, on anything related to earth or planetary sciences -- geology, solar system astronomy, atmospheric science, geophysics, geochemistry, you name it.

I have no idea how regular attendees manage the information overload of deciding which talks to attend. I wasn't sure how I would, either, but I started by going through the schedule for the day I'd be there, picking out a (way too long) list of potentially interesting talks, and saving them as lines in a file.

Now I had a file full of lines like:

1020      U22A    MS 303  Terrestrial Impact Cratering: New Insights Into the Cratering Process From Geophysics and Geochemistry II
Fine, except that I couldn't print out something like that -- printers stop at 80 columns. I could pass it through a program like "fold" to wrap the long lines, but then it would be hard to scan through quickly to find the talk titles and room numbers. What I really wanted was to wrap it so that the above line turned into something like:
1020      U22A    MS 303  Terrestrial Impact Cratering: New Insights
                          Into the Cratering Process From Geophysics
                          and Geochemistry II
But how to do that? I stared at it for a while, trying to figure out whether there was a clever vim substitute that could handle it. I asked on a couple of IRC channels, just in case there was some amazing Linux smart-wrap utility I'd never heard of. I was on the verge of concluding that the answer was no, and that I'd have to write a python script to do the wrapping I wanted, when Mikael emitted a burst of line noise:

Only it wasn't line noise. Seems Mikael just happened to have been reading about some of the finer points of vim regular expressions earlier that day, and he knew exactly the trick I needed -- that .\{72\}, which matches lines that are at least 72 characters long. And amazingly, that expression did something very close to what I wanted.

Or at least the first step of it. It inserts the first line break, turning my line into

1020      U22A    MS 303  Terrestrial Impact Cratering: New Insights
                          Into the Cratering Process From Geophysics and Geochemistry II
but I still needed to wrap the second and subsequent lines.

But that was an easier problem -- just do essentially the same thing again, but limit it to only lines starting with a tab. After some tweaking, I arrived at exactly what I wanted:

%s/^\(.\{,65\}\) \(.*\)/\1^M^I^I^I\2/

%g/^^I^I^I.\{58\}/s/^\(.\{,55\}\) \(.*\)/\1^M^I^I^I\2/
I had to run the second line two or three times to wrap the very long lines.

Devdas helpfully translated the second one into English: "You have 3 tabs, followed by 58 characters, out of which you match the first 55 and put that bit in $1, and the capture the remaining in $2, and rewrite to $1 newline tab tab tab $2."

Here's a more detailed breakdown:

Line one:
% Do this over the whole file
s/ Begin global substitute
^ Start at the beginning of the line
\( Remember the result of the next match
.\{,65\}_ Look for up to 65 characters with a space at the end
\) \( End of remembered pattern #1, skip a space, and start remembered pattern #2
.*\) Pattern #2 includes everything to the end of the line
/ End of matched pattern; begin replacement pattern
\1^M Insert saved pattern #1 (the first 65 lines ending with a space) followed by a newline
^I^I^I\2 On the second line, insert three tabs then saved pattern #2
/ End replacement pattern

Line two:
%g/ Over the whole file, only operate on lines with this pattern
^^I^I^I Lines starting with three tabs
.\{58\}/ After the tabs, only match lines that still have at least 58 characters (this guards against wrapping already wrapped lines when it's run repeatedly)
s/ Begin global substitute
^ Start at the beginning of the line
\( Remember the result of the next match
.\{,55\} Up to 55 characters
\) \( End of remembered pattern #1, skip a space, and start remembered pattern #2
.*\) Pattern #2 includes everything to the end of the line
/ End of matched pattern; begin replacement pattern
\1^M The first pattern (up to 55 chars) is one line
^I^I^I\2 Three tabs then the second pattern
/ End replacement pattern

Greedy and non-greedy brace matches

The real key is those curly-brace expressions, \{,65\} and \{58\} -- that's how you control how many characters vim will match and whether or not the match is "greedy". Here's how they work (thanks to Mikael for explaining).

The basic expression is {M,N} -- it means between M and N matches of whatever precedes it. (Vim requires that the first brace be escaped -- \{}. Escaping the second brace is optional.) So .{M,N} can match anything between M and N characters but "prefer" N, i.e. try to match as many as possible up to N. To make it "non-greedy" (match as few as possible, "preferring" M), use .{-M,N}

You can leave out M, N, or both; M defaults to 0 while N defaults to infinity. So {} is short for {0,∞} and is equivalent to *, while {-} means {-0,∞}, like a non-greedy version of *.

Given the string: one, two, three, four, five
,.\{}, matches , two, three, four,
,.\{-}, matches , two,
,.\{5,}, matches , two, three, four,
,.\{-5,}, matches , two, three,
,.\{,2}, matches nothing
,.\{,7}, matches , two,
,.\{5,7}, matches , three,

Of course, this syntax is purely for vim; regular expressions are unfortunately different in sed, perl and every other program. Here's a fun table of regexp terms in various programs.

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[ 12:44 Dec 20, 2007    More linux/editors | permalink to this entry | ]

Fri, 14 Dec 2007

XFCE dukes it out with Gnome; users lose

Looking for a volume control that might me installed on mom's XFCE4-based Xubuntu desktop, I tried running xfce4-mixer.

The mixer came up fine -- but after I exited, I discovered that my xchat had gone all wonky. None of my normal key bindings worked, my cursor was blinking, and the fonts used for tabs was about half its normal size. Over in my Firefox window, key bindings were also affected.

I've seen this sort of thing happen before with Gnome apps, and had found a way to solve it using gconf-editor. That app was not installed, so I installed it and discovered that it didn't help.

I tried killing the running gconfd-2, removing .gconf/ and .gconfd/ from my home directory, then removing the four gnome directories (.gnome/, .gnome2/, .gnome2_private/, and .gnome_private/). Nothing helped xchat (though Firefox did return to normal).

After much flailing and annoying people by restarting xchat repeatedly, it turned out the problem was that xfce-mixer had started a daemon called xfce-mcs-manager, which is like gconf, only different. Like gconf, it mucks with settings of all running gtk programs without asking first. It runs simultaneously with gconf, but overrides gconf, which in turn overrides the values set in ~/.gtkrc-2.0.

Killing xfce-mcs-manager caused my running xchat to revert to its normal settings.

... Well, *almost* revert. A few key bindings didn't get reset, as I discovered when I hit a ctrl-W to erase the last word and found myself disconnected from the channel. Another xchat restart, with xfce-mcs-manager not running, fixed that.

Aside from the ever-present issue of "Where do I look when some unfriendly program decides to change the settings in running applications?" (which begs the question, "What genius thought it would be a good idea to give any random app like a volume control the power to change settings in every other gtk application currently running on the system? And do they have their medications adjusted better now?") there's another reason this is interesting.

See, if an arbitrary app like xfce-mcs-manager can send a message to xchat to change key bindings like ctrl-W ... then maybe I could write a program that could send a similar message telling xchat to cancel those compiled-in bindings like ctrl-F and ctrl-L, ones that it doesn't allow the user to change. If I could get something like that working, I could use a standard xchat -- I'd no longer need to patch the source and build my own.

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[ 21:12 Dec 14, 2007    More linux | permalink to this entry | ]

Fri, 07 Dec 2007

Bug fixes? Why would we bother to ship bug fixes?

(A culture of regressions, part 2)

I've been running on Ubuntu's latest, "Gutsy gibbon", for maybe a month now. Like any release, it has its problems that I've needed to work around. Like many distros, these problems won't be fixed before the next release. But unlike other distros, it's not just lack of developer time; it turns out Ubuntu's developers point to an official policy as a reason not to fix bugs.

Take the case of the aumix bug. Aumix just plain doesn't work in gutsy. It prints, "aumix: SOUND_MIXER_READ_DEVMASK" and exits.

This turns out to be some error in the way it was compiled. If you apt-get the official ubuntu sources, build the package and install it yourself, it works fine. So somehow they got a glitch during the process of building it, and produced a bad binary.

(Minor digression -- does that make this a GPL violation? Shipping sources that don't match the distributed binary? No telling what sources were used to produce the binary in Gutsy. Not that anyone would actually want the sources for the broken aumix, of course.)

It's an easy fix, right? Just rebuild the binary from the source in the repository, and push it to the servers.

Apparently not. A few days ago, Henrik Nilsen Omma wrote in the bug:

This bug was nominated for Gutsy but does currently not qualify for a 7.10 stable release update (SRU) and the nomination is therefore declined. According the the SRU policy, the fix should already be deployed and tested in the current development version before an update to the stable releases will be considered. [ ... ] See:

Of course, I clicked on the link to receive enlightenment. Ubuntu's Stable Release page explains

Users of the official release, in contrast, expect a high degree of stability. They use their Ubuntu system for their day-to-day work, and problems they experience with it can be extremely disruptive. Many of them are less experienced with Ubuntu and with Linux, and expect a reliable system which does not require their intervention.
by way of explaining the official Ubuntu policy on updates:
Stable release updates will, in general, only be issued in order to fix high-impact bugs. Examples of such bugs include:
  • Bugs which may, under realistic circumstances, directly cause a security vulnerability
  • Bugs which represent severe regressions from the previous release of Ubuntu
  • Bugs which may, under realistic circumstances, directly cause a loss of user data

Clearly aumix isn't a security vulnerability or a loss of user data. But I could make a good argument that a package that doesn't work ... ever ... for anyone ... constitutes a severe regression from the previous version of that package.

Ubuntu apparently thinks that users get used to packages not working, and grow to like it. I guess that if you actually fixed packages that you broke, that would be disruptive to users of the stable release.

I'm trying to picture these Ubuntu target users, who embrace regressions and get upset when something that doesn't work at all gets fixed so that it works as it did in past releases. I can't say I've ever actually met a user like that myself. But evidently the Ubuntu Updates Team knows better.

Update: I just have to pass along Dave's comment: "When an organization gets to the point where it spends more energy on institutional processes for justifying not fixing something than on just fixing it -- it's over."

Update: Carla Schroder has also written about this.

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[ 11:21 Dec 07, 2007    More linux | permalink to this entry | ]

Thu, 06 Dec 2007

Shampoo marketing

[citrus shampoo] I bought a new bottle of shampoo. Like many shampoos, its label tries to promote it as a natural, healthy alternative for natural, healthy hair. To this end, it proclaims that it's "enriched with orange fruit extract and provitamin B5".

Leaving aside the question of "What's provitamin B5 and why should it be good to rub it on the outside of a dead keratin layer?", I like the colorful, natural, healthy looking picture on the front of the bottle.

The picture shows two halves of a sliced orange; a wedge of lime; and ... a watermelon?

Now, I know I'm not a botanist, but somehow I'd been unaware up to now that watermelon was a citrus fruit.

Amazing what you can learn simply from browsing the supermarket aisles!

[ 17:38 Dec 06, 2007    More humor | permalink to this entry | ]

Sat, 01 Dec 2007

More Tips on International Input

With what I learned last week, I've been able to type accented characters into GTK apps such as xchat, and a few other apps such as emacs. That's nice -- but I was still having trouble reading accented characters in mutt, or writing them in vim to send through mutt (darn terminal apps).

The biggest problem was the terminal. I was using urxvt, but it turns out that urxvt won't let me type any nonascii characters. It just ignores my multi-key sequences, or prints a space instead of the character I wanted. I have no idea why, but switching to plain ol' xterm solved that problem. Of course, I had to make sure that I was using a font that supported the characters I wanted (ISO 8859-1 or 8859-15 or something similar), which leaves out my favorite terminal font (Schumacher Clean bold), but Bitstream Vera Sans Mono bold is almost as readable.

Of course, it's important to have your locale variables set appropriately. There are several locale variables:

Which encodings to use for typing and displaying characters.
Which translations to use, in programs that offer them.
How to sort alphabetically (this one also affects whether ls groups capitalized filenames first).
Overrides any of the others.
The default, in case none of the other variables is set.
There are a few others which control very specific features like time, numbers, money, addresses and paper size: type locale to see all of them.

Once I switched to xterm, I was able to set either LANG or LC_CTYPE to either en_US.UTF-8 or en_US.ISO-8859-1. I set LC_COLLATE and LANG or LC_MESSAGES to C, so that I get the default (usually US) translations for programs and so that ls groups all the capitalized files first.

Along the way, I learned about yet another way to type accented characters.

setxkbmap -model pc104 -layout us -variant intl
switches to an international layout, at which point typing certain punctuation (like ' or ~) is assumed to be a prefix key. So instead of typing [Multi] ~ n, I can just type ~ n. The catch: it makes it harder to type quotes or tildes by themselves (you have to type a space after the quote or tilde).

Even faster, the international layout also offers shortcuts to many common characters with the "AltGr" key, which I'd heard about for years but never knew how to enable. AltGr is the right alt key, and typing, say, AltGr followed by n gives an ñ. You can see a full map at Wikipedia (AltGr characters are blue, quote prefixes are red).

To get back to a US non-international layout:

setxkbmap -model pc104 -layout us

Of course, these aren't the only keyboard layouts to choose from -- there are lots, plus you can define your own. And I was going to write a little bit about that, except it turns out they've changed it all around again since I last did that two years ago (don't you love the digital world?). So that will have to wait for another time.

But the place to start exploring is /usr/share/X11/xkb. The file symbols/us contains the definitions for those US keyboards, and I believe it's included via the files in the rules directory, probably rules/base, base.xml and base.lst. From there you're on your own. But the standard layouts probably follow the ones in the Wikipedia article on keyboard layouts

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[ 16:48 Dec 01, 2007    More linux | permalink to this entry | ]