byronc bits

pm-utils and Locked Screens

Tue, 06 Apr 2010 05:54:54 MDT

pm-utils seems to be the clear winner to userspace suspend and hibernate setup. It's a great back, but, for those of us who don't run a desktop environment with a power manager, there's one thing missing: screen locking. I'd like the screen to be locked when my computer resumes from either suspend or hibernate, and I don't want to run gnome-power-manager to get that functionality. So, 00lock-screen to the rescue. Just drop that file in /etc/pm/sleep.d and, as long as you have xscreensaver, gnome-screensaver, i3lock, or xlock setup, the screen will lock as your computer suspends or hibernates.

For the Archlinux users, it's already packaged in the AUR: pm-utils-screen-lock

OpenWRT on the D-Link DIR-615

Wed, 10 Mar 2010 06:41:01 MST

Last night, I finally got around to installing the OpenWRT 10.03 Beta on my D-Link DIR-615. The short version: it works and works well. There were only two surprises I ran into.

The first surprise is that the wireless drivers are not included in the install image. Running opkg update; opkg install kmod-ath9k takes care of that. The drivers are left out by design at least on this router and the WRT160NL. Bonus points to OpenWRT for allowing me to file a bug without creating an account on their bug tracker.

The second surprise is that the dynamic dns client doesn't know about DNS-O-Matic. I installed the ddns-scripts package and used the following config to get it working:

config 'service' 'myddns'
	option 'ip_source' 'network'
	option 'ip_network' 'wan'
	option 'check_unit' 'minutes'
	option 'enabled' '1'
	option 'domain' 'all.dnsomatic.com'
	option 'username' 'username'
	option 'password' 'password'
	option 'update_url' 'http://[USERNAME]:[PASSWORD]@updates.dnsomatic.com/nic/update?hostname=[DOMAIN]&myip=[IP]'
	option 'check_interval' '5'
	option 'force_interval' '480'
	option 'force_unit' 'hours'

gdb and pthread

Fri, 19 Feb 2010 21:33:22 MST

Error message translation time. Here's an error gdb gave me today:

[Thread debugging using libthread_db enabled]             
Cannot find new threads: generic error

Translation: Programs that use pthread functions should really be linked with the -lpthread option.

Scripting wireshark with lua

Wed, 09 Dec 2009 06:44:23 MST

While attempting to wrap some wireshark processing with a bash script, I discovered that I didn't need to write complex bash code at all, because wireshark has a built-in scripting language. Even better, it's a common scripting language: lua. It looks like Debian and its derivatives ship wireshark with lua support, but for everything else, you'll have to rebuild the package to enable it. There's a great page of examples and the api is really simple. And for those cases where you don't want to use the wireshark GUI, lua scripts work just fine with tshark.

If lua is overkill for the task at hand, tshark also offers decent control over what shows up in the output. If you want to see all HTTP requests and their request URI and method, without any other information about the packet, this tshark command will do the trick:

tshark -T fields -e http.request.method -e http.request.uri -R 'http'

View a Certificate

Wed, 20 May 2009 11:10:40 MDT

Yet another command I'll never remember unless I write it down. Here's how to view a certificate. In my case I was viewing a certificate that Mutt had stored:

openssl x509 -in .mutt_certs -noout -text

Saving ViM Macros

Wed, 11 Mar 2009 09:32:01 MDT

I use ViM macros (aka complex-repeat) all the time. Occasionally, I find that it would be nice to reuse one of my macros across editing sessions. Turns out it's pretty easy to save the macro. Just add a line like the following to a file that gets sourced when your file is opened by ViM (This example is from ~/.vim/ftplugin/rst.vim).

let @h = "yypVr"

Now, whenever I open a ReStructured Text file, I can hit @h and my macro will run.

Sparse Files and tar

Sun, 08 Mar 2009 18:50:42 MDT

GNU tar provides the -S option to efficiently handle sparse files. Of course it only works if you create the tarball with the -S option. That is all.

More Useful ViM Tags

Wed, 04 Mar 2009 20:35:04 MST

Frequently, I find myself writing C code that requires the use of struct ifreq. There are plenty of fields there and of course there are other structures that I never remember. I could always look in the headers, but it ends up being a good amount of digging before I find the real definition and all its accompanying pieces. So, I decided to let ctags and ViM do the work for me. I created ~/bin/update_local_tags with the following contents:

#!/bin/sh
[ -d ~/.localtags ] || mkdir ~/.localtags
ctags -f ~/.localtags/usrinclude.ctags --exclude=vector\*.hpp -R /usr/include >/dev/null 2>&1

Then I created ~/.vim/ftplugin/c.vim with the following contents:

setlocal tags+=$HOME/.localtags/usrinclude.ctags

For good measure I copied c.vim to cpp.vim so it would be loaded for C++ file types also.

Now I just have to run update_local_tags to generate a tag file for everything in /usr/include and ViM automatically includes that list whenever I edit a C or C++ file. Updating the tags file is still a manual process, I should probably attempt to hook it into apt. Observant readers will have noticed that I exclude vector*.hpp when generating the tags. Boost includes a few generated header files that match this pattern and swell the tag file to almost 750 MiB.

application/vnd.fdf and pdftk

Mon, 06 Oct 2008 20:40:24 MDT

So, if a webserver ever serves you a fdf file, you can view the resulting form with evince or your favorite pdf viewer. Just check the beginning of the fdf file to see which form the fields should be applied to and then run

pdftk form.pdf fill_form my.fdf output filledform.pdf

Using the verbatim Environment and listings Package with Beamer

Wed, 13 Aug 2008 22:11:25 MDT

I finally figured out how to make the verbatim environment work with Beamer. Beamer can't handle the following code:

\begin{frame}{A Title}
    \begin{verbatim}
    Don't mess with my text.
    \end{verbatim}
\end{frame}

To make it work, you need to include the fragile option for the frame. Example:

\begin{frame}[fragile]{A Title}
    \begin{verbatim}
    Don't mess with my text.
    \end{verbatim}
\end{frame}

If you use the listings package, the same trick works for the lstlistings environment.