I'm using latest Lubuntu Linux (13/04) here.
AFAIK, Processing isn't formally installed in any system.
Rather, its downloaded file is decompressed and thrown in some place you arbitrarily choose.
It's completely self-contained.
And to run it, you have to make "processing" file runnable.
Then, you have to choose where your own sketches gonna live.
That "sketch" folder is the home of your own libraries. And for many other things too.

What libraries are you searching, exactly?

i know what GoToLoop says but i'm speaking about the libraries that come with Processing: pdf, minim, net, serial, video...

the problem is that i want to update the library of minim but i don't find it and i only can create a new library called "minim" and then i have a conflict with these libraries

I don't know if the file hierarchy is the same than with Windows (the version I have), but I find them under the modes/java/libraries folder. The find tool is your friend, too...

okay! sorry, i had not searched good...

other problem is that i have an error with a code, is this:

1. // We will use MINIM as our Audio Library
   
   
   // To draw colored vertical lines that stand for
   
    
   
   // a song's waveform
   
   
   
   // Therefore we import it
   
   
   
   import ddf.minim.* ;
   
   
   
   // We create a Minim Object to manage audio
   
   
   
   Minim AudioManager;
   
   
   // We create an AudioPlayer Object to load a track (song)
   
   
   
   AudioPlayer MySong;
   
   
   
    
   
   
   
   // The Setup function that we'll be called only once
   
   
   
   void setup(){
   
   
     // Our window is 256 x 256 pixels
   
   
     size(256, 256);
   
    
   
     // We initialize the AudioManager object
   
   
     AudioManager = new Minim(this);
   
   
     // We use the "loadFile" method inside the "minim" object
   
   
   
     // to load an MP3 file, 256 samples everytime
   
   
   
     MySong = AudioManager.loadFile("Els Pets - Soroll.mp3",256);
   
   
     // We start playing the track/song/file
   
   
   
     MySong.play();
   
   
     // Our lines we'll be 5 pixels wide
    
   
   
   
   }

when i compile it has this error:

Listening for transport dt_socket at address: 8821
==== JavaSound Minim Error ====
==== Don't know the ID3 code TXXX

==== JavaSound Minim Error ====
==== Don't know the ID3 code TXXX

==== JavaSound Minim Error ====
==== Don't know the ID3 code TSSE

==== JavaSound Minim Error ====
==== Couldn't open the line: line with format PCM_SIGNED 44100.0 Hz, 16 bit, stereo, 4 bytes/frame, little-endian not supported.

==== JavaSound Minim Error ====
==== Unable to return a SourceDataLine: unsupported format - PCM_SIGNED 44100.0 Hz, 16 bit, stereo, 4 bytes/frame, little-endian

The ID3 "errors" are just warning, just ignore them.

I don't know if the file hierarchy is the same than with Windows (the version I have)...

AFAIK, the only diff. among OS versions is the launcher executable. It's Java anyways! 
I daresay that Processing should come as 1 version for Windows, Linux and MacOS.
Just include all launchers and all's done!
Also, it should stopping coming w/ an old bundled Java and use the OS's 1.
All Java apps I see merely state that Java is needed for them to run.
Same for .Net framework based apps!

i have solved the problem with the mp3 when i have deleted the old library of minim and replaced it with the new library.

What i don't know is how to make a processing file runnable

You mean generate a compiled Java program? I use <CTRL> + E.

@GoToLoop: not really, there are also the native libraries, like those for OpenGL, serial, and so on. Bundling all versions for all OSes would bloat even more an already big download.

Bundling all versions for all OSes would bloat even more an already big download.

The Linux launcher file ("processing") is merely 2.6 KiB! Just a tickle! 

Re-read my answer. It is not only the launcher, but also the OpenGL binaries (but argument is void there: small files, already shipped for all OSes for Windows), the w32api files of launch4j, unnecessary on other systems, the serial binaries (actually, they are also shipped for all OSes, and given we also get the build files, like build.xml, .classpath or .settings, I am suspecting an under-optimized bundler, it should be more selective), and so on.