Shallow Thoughts : : Mar

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

Sat, 26 Mar 2016

Debian: Holding packages you build from source, and rebuilding them easily

Recently I wrote about building the Debian hexchat package to correct a key binding bug.

I built my own version of the hexchat packages, then installed the ones I needed:

dpkg -i hexchat_2.10.2-1_i386.deb hexchat-common_2.10.2-1_all.deb hexchat-python_2.10.2-1_i386.deb hexchat-perl_2.10.2-1_i386.deb

That's fine, but of course, a few days later Debian had an update to the hexchat package that wiped out my changes.

The solution to that is to hold the packages so they won't be overwritten on the next apt-get upgrade:

aptitude hold hexchat hexchat-common hexchat-perl hexchat-python

If you forget which packages you've held, you can find out with aptitude:

aptitude search '~ahold'

Simplifying the rebuilding process

But now I wanted an easier way to build the package. I didn't want to have to search for my old blog post and paste the lines one by one every time there was an update -- then I'd get lazy and never update the package, and I'd never get security fixes.

I solved that with a zsh function:

newhexchat() {
    # Can't set errreturn yet, because that will cause mv and rm
    # (even with -f) to exit if there's nothing to remove.
    cd ~/outsrc/hexchat
    echo "Removing what was in old previously"
    rm -rf old
    echo "Moving everything here to old/"
    mkdir old
    mv *.* old/

    # Make sure this exits on errors from here on!
    setopt localoptions errreturn

    echo "Getting source ..."
    apt-get source hexchat
    cd hexchat-2*
    echo "Patching ..."
    patch -p0 < ~/outsrc/hexchat-2.10.2.patch
    echo "Building ..."
    debuild -b -uc -us
    echo
    echo 'Installing' ../hexchat{,-python,-perl}_2*.deb
    sudo dpkg -i ../hexchat{,-python,-perl}_2*.deb
}

Now I can type newhexchat and pull a new version of the source, build it, and install the new packages.

How do you know if you need to rebuild?

One more thing. How can I find out when there's a new version of hexchat, so I know I need to build new source in case there's a security fix?

One way is the Debian Package Tracking System. You can subscribe to a package and get emails when a new version is released. There's supposed to be a package tracker web interface, e.g. package tracker: hexchat with a form you can fill out to subscribe to updates -- but for some packages, including hexchat, there's no form. Clicking on the link for the new package tracker goes to a similar page that also doesn't have a form.

So I guess the only option is to subscribe by email. Send mail to pts@qa.debian.org containing this line:

subscribe hexchat [your-email-address]
You'll get a reply asking for confirmation.

This may turn out to generate too much mail: I've only just subscribed, so I don't know yet. There are supposedly keywords you can use to limit the subscription, such as upload-binary and upload-source, but the instructions aren't at all clear on how to include them in your subscription mail -- you say keyword, or keyword your-email, so where do you put the actual keywords you want to accept? They offer no examples.

Use apt to check whether your version is current

If you can't get the email interface to work or suspect it'll be too much email, you can use apt to check whether the current version in the repository is higher than the one you're running:

apt-cache policy hexchat

You might want to automate that, to make it easy to check on every package you've held to see if there's a new version. Here's a little shell function to do that:

# Check on status of all held packages:
check_holds() {
    for pkg in $( aptitude search '~ahold' | awk '{print $2}' ); do
        policy=$(apt-cache policy $pkg)
        installed=$(echo $policy | grep Installed: | awk '{print $2}' )
        candidate=$(echo $policy | grep Candidate: | awk '{print $2}' )
        if [[ "$installed" == "$candidate" ]]; then
            echo $pkg : nothing new
        else
            echo $pkg : new version $candidate available
        fi
    done
}

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[ 11:11 Mar 26, 2016    More linux | permalink to this entry | comments ]

Thu, 17 Mar 2016

Changing X brightness and gamma with xrandr

I switched a few weeks ago from unstable ("Sid") to testing ("Stretch") in the hope that my system, particularly X, would break less often. The very next day, I updated and discovered I couldn't use my system at night any more, because the program I use to reduce the screen brightness by tweaking X gamma no longer worked. Neither did other related programs, such as xgamma and xcalib.

The Dell monitor I use doesn't have reasonable hardware brightness controls: strangely, the brightness button works when the monitor is connected over VGA, but if I want to use the sharper HDMI connection, brightness adjustment no longer works. So I depend on software brightness adjustment in order to use my computer at night when the room is dim.

Fortunately, it turns out there's a workaround. xrandr has options for both brightness and gamma:

xrandr --output HDMI1 --brightness .5
xrandr --output HDMI1 --gamma .5:.5:.5

I've always put xbrightness on a key, so I can use a function key to adjust brightness interactively up and down according to conditions. So a command that sets brightness to .5 or .8 isn't what I need; I need to get the current brightness and set it a little brighter or a little dimmer. xrandr doesn't offer that, so I needed to script it.

You can get the current brightness with

xrandr --verbose | grep -i brightness

But I was hoping there would be a more straightforward way to get brightness from a program. I looked into Python bindings for xrandr; there are some, but with no documentation and no examples. After an hour of fiddling around, I concluded that I could waste the rest of the day poring through the source code and trying things hoping something would work; or I could spend fifteen minutes using subprocess.call() to wrap the command-line xrandr.

So subprocesses it was. It made for a nice short script, much simpler than the old xbrightness C program that used <X11/extensions/xf86vmode.h> and XF86VidModeGetGammaRampSize(): xbright on github.

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[ 11:01 Mar 17, 2016    More linux | permalink to this entry | comments ]

Tue, 08 Mar 2016

Juniper allergy season

It's spring, and that means it's the windy season in New Mexico -- and juniper allergy season.

When we were house-hunting here, talking to our realtor about things like local weather, she mentioned that spring tended to be windy and a lot of people got allergic. I shrugged it off -- oh, sure, people get allergic in spring in California too. Little did I know.

A month or two after we moved, I experienced the worst allergies of my life. (Just to be clear, by allergies I mean hay fever, sneezing, itchy eyes ... not anaphylaxis or anything life threatening, just misery and a morbid fear of ever opening a window no matter how nice the temperature outside might be.)

[Female (left) and male junipers in spring]
I was out checking the mail one morning, sneezing nonstop, when a couple of locals passed by on their morning walk. I introduced myself and we chatted a bit. They noticed my sneezing. "It's the junipers," they explained. "See how a lot of them are orange now? Those are the males, and that's the pollen."

I had read that juniper plants were either male or female, unlike most plants which have both male and female parts on every plant. I had never thought of junipers as something that could cause allergies -- they're a common ornamental plant in California, and also commonly encountered on trails throughout the southwest -- nor had I noticed the recent color change of half the junipers in our neighborhood.

But once it's pointed out, the color difference is striking. These two trees, growing right next to each other, are the same color most of the year, and it's hard to tell which is male and which is female. But in spring, suddenly one turns orange while the other remains its usual bright green. (The other season when it's easy to tell the difference is late fall, when the female will be covered with berries.)

Close up, the difference is even more striking. The male is dense with tiny orange pollen-laden cones.

[Female juniper closeup] [male juniper closeup showing pollen cones]

A few weeks after learning the source of my allergies, I happened to be looking out the window on a typically windy spring day when I saw an alarming sight -- it looked like the yard was on fire! There were dense clouds of smoke billowing up out of the trees. I grabbed binoculars and discovered that what looked like fire smoke was actually clouds of pollen blowing from a few junipers. Since then I've gotten used to seeing juniper "smoke" blowing through the canyons on windy spring days. Touching a juniper that's ready to go will produce similar clouds.

The good news is that there are treatments for juniper allergies. Flonase helps a lot, and a lot of people have told me that allergy shots are effective. My first spring here was a bit miserable, but I'm doing much better now, and can appreciate the fascinating biology of junipers and the amazing spectacle of the smoking junipers (not to mention the nice spring temperatures) without having to hide inside with the windows shut.

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[ 20:20 Mar 08, 2016    More nature | permalink to this entry | comments ]

Fri, 04 Mar 2016

Recipe: Easy beef (or whatever) jerky

You don't need a special smoker or dehydrator to make great beef jerky.

Winter is the time to make beef jerky -- hopefully enough to last all summer, because in summer we try to avoid using the oven, cooking everything outside so as not to heat up the house. In winter, having the oven on for five hours is a good thing.

It took some tuning to get the flavor and the amount of saltiness right, but I'm happy with my recipe now.

Beef jerky

Ingredients

Directions

Heat water slightly (30-40 sec in microwave) to help dissolve salt. Mix all ingredients except beef.

Cut meat into small pieces, trimming fat as much as possible.

Marinate in warm salt solution for 15 min, stirring occasionally. (For pork, you might want a shorter marinating time. I haven't tried other meats.)

Set the oven on its lowest temperature (170F here).

Lay out beef on a rack, with pieces not touching or overlapping.
Nobody seems to sell actual cooking racks, but you can buy "cooling racks" for cooling cookies, which seem to work fine for jerky. They're small so you probably need two racks for a pound of beef.

Ideally, put the rack on one oven shelf with a layer of foil on the rack below to catch the drips.
You want as much air space as possible under the meat. You can put the rack on a cookie sheet, but it'll take longer to cook and you'll have to turn the meat halfway through. Don't lay the beef directly on cookie sheet or foil unless you absolutely can't find a rack.

Cook until sufficiently dry and getting hard, about 4 to 4-1/2 hours at 170F depending on how dry you like your jerky. Drier jerky will keep longer unrefrigerated, but it's not as tasty. I cook mine a little less and store it in the fridge when I'm not actually carrying it hiking or traveling.

If you're using a cookie sheet, turn the pieces once at around 2-3 hours when the tops start to look dry and dark.

Tip: if you're using a rack without a cookie sheet, a fork wedged between the bars of the rack makes it easy to remove a rack from the oven.

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[ 12:24 Mar 04, 2016    More recipes | permalink to this entry | comments ]