May 19, 2012

revdep-rebuild doesn't detect qt-core's dependency on

It's a known issue, bug #413541. The end result is weird, because revdep-rebuild tells you that everything is fine, yet some apps display errors (they still launch though):

Unable to load library icui18n "Cannot load library icui18n: ( cannot open shared object file: No such file or directory)"

The workaround is to re-emerge qt-core (more packages might be affected).

If you wonder what's the root cause, it's using dlopen (in this case in qt-core) instead of linking directly (e.g. ELF DT_NEEDED entry) with given library.

In binary-only world, using dlopen may make sense sometimes. Package names, versions, and library SONAMEs vary between distros, so it's difficult to create a single package that works with multiple distros. It may be easier to dlopen the needed libraries (sometimes even trying different SONAMEs), and fail gracefully in case they are missing (e.g. just disable some optional functionality).

That's what Qt is doing here. However, in Open Source world, where software is packaged by distributions, the above case should be handled by linking directly (DT_NEEDED), allowing tools like revdep-rebuild to detect the breakage.

Other distributions are hitting this problem too, see e.g. and

May 12, 2012

ffmpeg saves the day (.mts files)

If you need to convert .mts files to .mov (so that e.g. iMovie can import them), I found ffmpeg to be the best tool for the task (I don't want to install and run "free format converters" that are usually Windows-only and come from untrusted sources). This post is inspired by iMovie and MTS blog post.

First I tried just changing the container:

for x in *.MTS; do ffmpeg -i ${x} -c copy ${x/.MTS/.mov}; done

But QuickTime could not play sound from those files because of AC-3 codec. Also, the quality of the video playback was very poor. The other command I tried was:

for x in *.MTS; do ffmpeg -i ${x} -vcodec copy -acodec mp2 -ac 2 ${x/.MTS/.mov}; done

Now QuickTime was able to play the sound, but problems with video remained. iMovie was unable to import the resulting files anyway (silently: I got no error message, just nothing happened when trying to import).

The final command that is proven to work well is this:

for x in *.MTS; do ffmpeg -i ${x} -vcodec mpeg1video -acodec mp2 -ac 2 -sameq ${x/.MTS/.mov}; done

The video has been converted perfectly, and iMovie successfully imported the movies. Note the useful bash substitution of extension, ${x/.MTS/.mov}. Enjoy!

May 4, 2012

Another reason why SELinux's neverallow is very useful

I'm only beginning my experiments with SELinux, and neverallow (which is basically an assertion that prevents inserting certain allow rules) seemed a bit weird to me.

While experimenting with some local policies though, after an update (selinux-base-policy and other sec-policy packages) my local policy triggered a neverallow rule about sys_module capability being unnecessarily granted.

In fact, re-compiling the local policy and loading the new version made the error disappear. Now this is indeed useful, because binary policy files are arguably harder to inspect, and if they get out of sync with the base policy, it's easy to introduce errors like in this case.

Another conclusion is that learning takes time: it was the update that triggered this situation. I wonder what else awaits me in the SELinux land. ;-)