% ar m God
ar: God does not exist

Obviously thats a very old and used joke, nowdays we’re much more advanced than that:

$ ar m God
$ ar: creating God ]]> http://nicolasb.com.ar/2010/07/oh-my-god/feed/ 0 http://nicolasb.com.ar/2010/07/elvis-is-alive/ http://nicolasb.com.ar/2010/07/elvis-is-alive/#comments Tue, 06 Jul 2010 11:42:31 +0000 nico http://nicolasb.com.ar/?p=924 Unix trivia day: in the olden days of the 90’s there were a lot of Unix boxes out there named “elvis”. Nowdays it’s not uncommon to find one, either. Have you ever wondered why are there so many boxes called elvis?

This is related to Solaris’ ping command. When you ping $HOST it prints “$HOST is alive” (if it’s responding the pings), thus elvis is alive!

Quite a progress I’d say, as these are mostly programs I use which don’t come in the default install (even though they should). You know, I even have hopes for the sound system in my notebook this time…

Doing some research on the subject I wrote down a list of the thought process which led my to an (inconclusive) answer:

1. First we should define what a binary is for us: When we talk about a binary we are usually thinking about a compiled binary file, not an interpreted script file like Ruby or Python. Those are for people who like things to actually work, so let’s focus on a compiled executable file, like a C/C++ application.

2. Defining compiled file: What could it be other than a sequence of bytes the microprocessor can understand? Yes, that’s right, it’s sort of interpreted code, only there’s electronics behind, not more code. This brings us to the first interesting conclusion: the executable must be (leaving emulators aside) compatible with the architecture you’re on. Running Sparc? Well then, the binary better be compiled for Sparc because otherwise to the uP will not make any sense.

3. Format: as any other thing, a binary file must have a format. That is a standard which defines the structure the file will follow. ELF is the binary format for Linux and it’s quite standard. Of course, if the binary format is a standard then we should get perfect portability between different platforms running on equal architecture. Unfortunately that’s not the case.

4. (Cont’d) Why don’t we? The binary depends not only on compile time “stuff” but a loading time linking occurs: the executable binary will get linked with the system files like glibc, or any other dependency on a shared library it may have.

So, what are the keypoints for Linux binary portability? Architecture, binary format and system libraries.

Of course, making the executable run is only part of the equation, as running and segfaulting on the spot is not so nice either. For this last part you’ll have to closely follow the standards defined by POSIX for paths and stuff like that.

Epilogue

As an epilogue, we could add that Windows binary compatibility tends to be great. Running binaries from 12 years back is no small feat, yet this leads to a whole lot of other problems: an incredible complex loader, security bugs, backwards compatibility headaches, et al. The old new thing is a great source of information for this topics, I’m quite illiterate about Windows binaries nowdays

Followup links

• http://evanjones.ca/portable-linux-binaries.html
• http://autopackage.org/docs/devguide/ch07.html (I swear this one was working when I wrote this text… a year ago)

Oh, talking about binaries:

In my case the sound starts in mute. I know it’s a problem with pulse (which is a WTF in itself) and alsa, I don’t really care what’s the problem though, I just want to play my mp3s collection without having to carefully turn the knobs up to eleven in alsamixer.

After trying a lot of the “solutions” found on the internets I’ve decided the best thing to do, short of switching back to windows me, is adding the following to my “fix_ubuntu_fuckups.sh” start script, which already contains my dual-screen pseudofix:

This sets alsamixer to normal volume levels. As for the real fix, I’ll wait till the next Ubuntu version. I wonder which sound subsystem will they chose next time.

To fix this problem (more like hacking it away, actually) I keep a handy bash script in the top left corner on my desktop:

Also, as I have two nice rotable monitors at work it’s nice that now Ubuntu supports actually rotating the picture displayed in the monitor (thanks Ubuntu for coming up to speed… with windows 98, that is). Obviously I keep another script for this, as it doesn’t really work by default:

Even though I love bashing Ubuntu (and bash) I’m quite confident most, if not all, of this issues will be gone in future versions of the OS.

* Right click the file for which you want to change default associations and click properties
* Select “open with” tab
* …
* Profit!

The scheduler locking policy defines when will thread context swtiches occur. If you are debuging a thead and don’t want to be bothered by another then just lock the scheduler.

gdb has a default scheduling locking which defaults to “most annoying”, but fortunately you can easily change it:

set scheduler-locking

The possible values are:

• off: Disable locking, switches threads whenever gdb damn pleases
• on: Enable locking, won’t (ever) switch threads. Beware of deadlocks!
• step: Disable locking while running only

Hopefully this will save you some time.

Anyway, this is the part of the script I came up with to get the enum elements:

cat enum_definition.h | sed -n ‘/enum OID/,/\}\;/ s/\(.*\)/\1/p’

Nice voodoo, isn’t it? How the hell are you supposed to understand that? Well, you’re not, sed is write-only-code, but you can try reading http://www.grymoire.com/Unix/Sed.html#toc-uh-25, a great sed introduction.

Have fun!