How to install a network printer at CERN under Ubuntu

Installing a driver at CERN is kind of a puzzle, unless you run Windows or SLC. Unfortunately there are no tutorials how to do that. This is why I came up with the following, somewhat hackerish, solution:

1. Install packages libnet-ldap-perl and cups on your system using apt-get
2. Download the lpadmincern RPM package.
3. Unpack it.
4. Replace inside lpadmincern.pl

   my $cupsc='/sbin/service cups reload';

   with

   my $cupsc='/usr/sbin/service cups reload';

5. Replace
   

$command="LC_ALL=C /usr/sbin/lpadmin -p $prt->{printerName} -L \"$prt->{location}\" -D \"$prt->{description}\" -v $uri $duplex $media -o printer-is-shared=false -E";

with

$command="LC_ALL=C /usr/sbin/lpadmin -p $prt->{printerName} -L \"$prt->{location}\" -P $prt->{ppdfile} -D \"$prt->{description}\" -v $uri $duplex $media -o printer-is-shared=false -E";

Apparently this got replaced in the meanwhile.
6. install libnet-ldap-perl
7. Find your desired printer at CERN printing service
8. Move the whole directory to /usr/share/lpadmincern, otherwise it would complain about a missing directory.
9. Run

   perl lpadmincern.pl --add [your-printer-name-here]

How to check number of cores per CPU

echo $(($((`cat /proc/cpuinfo | grep 'processor' | sort -n | wc -l`))/$((`cat /proc/cpuinfo | grep "physical id" | sort -n | uniq | wc -l`))))

How to do a platform-independent path join in Java

Today I had to join a file path with its parent directory path. I could this simply by joining strings with "/", but this solution is not portable to non *nix systems. In Python I would write:

import os.path

parent = "a/b/c"
filename = "efg"
joined = os.path.join(parent, filename)

But what is Java equivalent? It turns out that the best way is to use java.io.File. One can do:

File parent = new File("a/b/c");
File file = new File("efg");
String joined = new File(parent, file).getPath();

The last line is to go back to String world, but possibly you don't have to.

Why we all love Maven

Synchronized print in Python

Today I faced a problem where I had to print to the standard output in a synchronized way. I put the following code in a file named rpython.py

from __future__ import print_function
from threading import Lock

_global_lock = Lock()
_old_print = print 

def print(*a, **b):
        with _global_lock:
                _old_print(*a, **b)

Now, in every Python module that requires synchronized printing I typed:

from __future__ import print_function
from rpython import print

Alternatively, if you don't want to shadow the default printing you can type:

from __future__ import print_function
from rpython import print as rprint

Have a nice, synchronized day.

EDIT: I should have started with a clear statement that Python's print is not synchronized in any way. Multiple threads writing concurrently to any stream can interfere and usually they do that, so as an effect you get a random mixture of massages which looks really ugly.

util.NativeCodeLoader: Unable to load native-hadoop library for your platform.

Problem: when launching a hadoop-based app one can encounter message

WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... 
using builtin-java classes where applicable

Solution: type following command in the command line. The path may vary depending on your platform and hadoop version

export LD_LIBRARY_PATH=/usr/lib/hadoop-0.20-mapreduce/lib/native/Linux-amd64-64

How to build jar with Maven containing nothing but dependencies

Today I came across a problem where I had to split my project into two jars: one containing my project's classes and the other one with dependencies. The former got changed every time I made some changes in the source files. The latter was basically constant throughout the development. This facilitates me the deployment of my application. Previously after each improvement I had to transfer a big-fat-and-ugly *-jar-with-dependencies.jar and that took ten good minutes as the file weights 189MB. It turned out that dependencies weight.. 189MB and my compiled classes 45KB. Below the xml that I placed in src/main/resources/assemblies/only-deps.xml

  
  only-deps
  
    jar
  
  false
  
    
      /
      false
      true
      runtime
    
  

and a profile that I added to the main pom.xml:

        
            only-deps
            
                
                    
                        org.apache.maven.plugins
                        maven-assembly-plugin
                        
                            
                                src/main/resources/assemblies/only-deps.xml
                            
                        
                        
                            
                                package
                                create-my-bundle
                                
                                    single
                                
                            
                        
                    
                
            
        

Run the whole thing with mvn install -P only-deps.