Fix display size on libvirt/Qemu guest

Lot of times I find myself of VM that does not correctly resize the screen display and that is literally nuisance. So, here is quick and dirty fix for this.

First you need to find out information about your display with following command:

xrandr -q

And you will see output like this:

Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 8192 x 8192
Virtual-0 connected primary 1920×1080+0+0 0mm x 0mm
1024×768      59.92 +
1920×1200     59.88
1920×1080     59.96*
1600×1200     59.87
1680×1050     59.95
1400×1050     59.98
1280×1024     59.89
1440×900      59.89
1280×960      59.94
1280×854      59.89
1280×800      59.81
1280×720      59.86
1152×768      59.78
800×600       59.86
848×480       59.66
720×480       59.71
640×480       59.38
Virtual-1 disconnected
Virtual-2 disconnected
Virtual-3 disconnected

This tells you the currently configured screens and the resolutions. In my case, the only connected screen as seen above is “Virtual-0“. Now, time to do the magic.

You just need to set the correct display/screen size with following command:

xrandr --output Virtual-0 --mode 1920x1200

Also, if you need to add a new resolution, first you need to create a modeline with following command:

cvt 1200 1024

You will get output like :

# 1200×1024 59.82 Hz (CVT) hsync: 63.59 kHz; pclk: 101.75 MHz
Modeline “1200x1024_60.00”  101.75  1200 1280 1400 1600  1024 1027 1037 1063 -hsync +vsync

 

and then set that with:

xrandr --output Virtual-0 --mode 1200x1024

Hope this helps you do away with some really pathetic display sizes in VM 🙂

Getting Started with Elixir Programming Language

If you have been reading blog posts, hacker news threads, your favorite developers tweets or listening to podcasts, at this point you’ve probably heard about the Elixir programming language. The language was created by José Valim, a well known developer in the open-source world. You may know him from the Ruby on Rails MVC framework or from devise and simple_form ruby gems him and his co-workers from the Plataformatec have been working on in the last few years.

According the José Valim, Elixir was born in 2011. He had the idea to build the new language due the lack of good tools to solve the concurrency problems in the ruby world. At that time, after spending time studying concurrency and distributed focused languages, he found two languages that he liked, Erlang and Clojure which run in the JVM. He liked everything he saw in the Erlang language (Erlang VM) and he hated the things he didn’t see, like polymorphism, metaprogramming and language extendability attributes which Clojure was good at. So, Elixir was born with that in mind, to have an alternative for Clojure and a dynamic language which runs in the Erlang Virtual Machine with good extendability support.

Getting Started with Elixir Programming Language

Elixir describes itself as a dynamic, functional language with immutable state and an actor based approach to concurrency designed for building scalable and maintainable applications with a simple, modern and tidy syntax. The language runs in the Erlang Virtual Machine, a battle proof, high-performance and distributed virtual machine known for its low latency and fault tolerance characteristics.

Before we see some code, it’s worth saying that Elixir has been accepted by the community which is growing. If you want to learn Elixir today you will easily find books, libraries, conferences, meetups, podcasts, blog posts, newsletters and all sorts of learning sources out there as well as it was accepted by the Erlang creators.

Let’s see some code!

Install Elixir:

Installing Elixir is super easy in all major platforms and is an one-liner in most of them.

Arch Linux

Elixir is available on Arch Linux through the official repositories:

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pacman -S elixir

Ubuntu

Installing Elixir in Ubuntu is a bit tidious. But it is easy enough nonetheless.

1
2
3
4
wget https://packages.erlang-solutions.com/erlang-solutions_1.0_all.deb && sudo dpkg -i erlang-solutions_1.0_all.deb
apt-get update
apt-get install esl-erlang
apt-get install elixir

OS X

Install Elixir in OS X using Homebrew.

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brew install elixir

Meet IEx

After the installation is completed, it’s time to open your shell. You will spend a lot of time in your shell if you want to develop in Elixir.

Elixir’s interactive shell or IEx is a REPL – (Read Evaluate Print Loop) where you can explore Elixir. You can input expressions there and they will be evaluated giving you immediate feedback. Keep in mind that your code is truly evaluated and not compiled, so make sure not to run profiling nor benchmarks in the shell.

The Break Command

There’s an important thing you need to know before you start the IEx RELP – how to exit it.

You’re probably used to hitting

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CTRL+C

to close the programs running in the terminal. If you hit

1
CTRL+C

in the IEx RELP, you will open up the Break Menu. Once in the break menu, you can hit

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CTRL+C

again to quit the shell as well as pressing

1
a

.

I’m not going to dive into the break menu functions. But, let’s see a few IEx helpers!

Helpers

IEx provides a bunch of helpers, in order to list all of them type:

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h()

.

And this is what you should see:

Those are some of my favorites, I think they will be yours as well.

  • 1
    h

    as we just saw, this function will print the helper message.

  • 1
    h/1

    which is the same function, but now it expects one argument.

For instance, whenever you want to see the documentation of the

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String
1
strip/2

method you can easily do:

Probably the second most useful IEx helper you’re going to use while programming in Elixir is the

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c/2

, which compiles a given elixir file (or a list) and expects as a second parameter a path to write the compiled files to.

Let’s say you are working in one of the http://exercism.io/ Elixir exersices, the Anagram exercise.

So you have implemented the

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Anagram

module, which has the method

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match/2

in the anagram.exs file. As the good developer you are, you have written a few specs to make sure everything works as expected as well.

This is how your current directory looks:

Now, in order to run your tests against the Anagram module you need to run/compile the tests.

As you just saw, in order to compile a file, simply invoke the

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elixir

executable passing as argument path to the file you want to compile.

Now let’s say you want to run the IEx REPL with the Anagram module accessible in the session context. There are two commonly used options. The first is you can require the file by using the options

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-r

, something like

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iex -r anagram.exs

. The second one, you can compile right from the IEx session.

Simple, just like that!

Ok, what about if you want to recompile a module? Should you exit the IEx, run it again and compile the file again? Nope! If you have a good memory, you will remember that when we listed all the helpers available in the IEx RELP, we saw something about a recompile command. Let’s see how it works.

Notice that this time, you passed as an argument the module itself and not the file path.

As we saw, IEx has a bunch of other useful helpers that will help you learn and understand better how an Elixir program works.

Basics of Elixir Types

Numbers

There are two types of numbers. Arbitrary sized integers and floating points numbers.

Integers

Integers can be written in the decimal base, hexadecimal, octal and binary.

As in Ruby, you can use underscore to separate groups of three digits when writing large numbers. For instance you could right a hundred million like this:

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100_000_000

Octal:

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0o444

Hexdecimal:

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0xabc

Binary:

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0b1011

Floats

Floare are IEEE 754 double precision. They have 16 digits of accuracy and a maximum exponent of around 10308.

Floats are written using a decimal point. There must be at least one digit before and after the point. You can also append a trailing exponent. For instance 1.0, 0.3141589e1, and 314159.0-e.

Atoms

Atoms are constants that represent names. They are immutable values. You write an atom with a leading colon

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:

and a sequence of letters, digits, underscores, and at signs

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@

. You can also write them with a leading colon

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:

and an arbitrary sequence of characters enclosed by quotes.

Atoms are a very powerful tool, they are used to reference erlang functions as well as keys and Elixir methods.

Here are a few valid atoms.

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:name, :first_name, :"last name",  :===, :[email protected]_question?

Booleans

Of course, booleans are true and false values. But the nice thing about them is at the end of the day, they’re just atoms.

Strings

By default, strings in Elixir are UTF-8 compliant. To use them you can have an arbitrary number of characters enclosed by

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"

or

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'

. You can also have interpolated expressions inside the string as well as escaped characters.

Be aware that single quoted strings are actually a list of binaries.

Anonymous Functions

As a functional language, Elixir has anonymous functions as a basic type. A simple way to write a function is

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fn (argument_list) -> body end

. But a function can have multiple bodies with multiple argument lists, guard clauses, and so on.

Dave Thomas, in the Programming Elixir book, suggests we think of fn…end as being the quotes that surround a string literal, where instead of returning a string value we are returning a function.

Tuples

Tuple is an immutable indexed array. They are fast to return its size and slow to append new values due its immutable nature. When updating a tuple, you are actually creating a whole new copy of the tuple self.

Tuples are very often used as the return value of an array. While coding in Elixir you will very often see this,

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{:ok, something_else_here}

.

Here’s how we write a tuple:

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{?a,?b,?c}

.

Pattern Matching

I won’t be able to explain everything you need to know about Pattern Matching, however what you are about to read covers a lot of what you need to know to get started.

Elixir uses

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=

as a match operator. To understand this, we kind of need to unlearn what we know about

1
=

in other traditional languages. In traditional languages the equals operator is for assignment. In Elixir, the equals operators is for pattern matching.

So, that’s the way it works values in the left hand side. If they are variables they are bound to the right hand side, if they are not variables elixir tries to match them with the right hand side.

Pin Operator

Elixir provides a way to always force pattern matching against the variable in the left hand side, the pin operator.

Lists

In Elixir, Lists look like arrays as we know it from other languages but they are not. Lists are linked structures which consist of a head and a tail.

Keyword Lists

Keyword Lists are a list of Tuple pairs.

You simply write them as lists. For instance: [{:one, 1}, 2, {:three, 3}]. There’s a shortcut for defining lists, here’s how it looks: [one: 1, three: 3].

In order to retrieve an item from a keyword list you can either use:

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Keyword.get([{:one, 1}, 2, {:three, 3}], :one)

Or use the shortcut:

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[{:one, 1}, 2, {:three, 3}][:one]

Because keyword lists are slow when retrieving a value, in it is an expensive operation, so if you are storing data that needs fast access you should use a Map.

Maps

Maps are an efficient collection of key/value pairs. The key can have any value you want as a key, but usually should be the same type. Different from keyword lists, Maps allow only one entry for a given key. They are efficient as they grow and they can be used in the Elixir pattern matching in general use maps when you need an associative array.

This article originally appeared on Toptal

Fix weird flux menu

Some distro’s just add all the items under single menu and thus the menu itself becomes unusable because of the number of items in the submenu and this I did not like and hence ceated this simply python script to fix that. For using the script, back up you “menu” file, redirect the output of this script to ‘menu’ file again.

 

#!/bin/python

F = open("~/.fluxbox/menu", "r")
count=0
mkc=1
started=0

for line in F:
    print line.rstrip()

    if '[submenu]' in line.lower() and started == 1:
        print '[end]'

    if '[end]'  in line.lower():
        count=0
        mkc=1
        if started > 0:
             started=0
             # print "Count is {}".format(count)
             # print "Started is {}".format(started)
             print '[end]'
    if '[exec]'  in line.lower():
        if count > 15 :
            if started > 0:
                started=0
                print '[end]'
                # print "Count is {}".format(count)
                # print "Started is {}".format(started)
            print '[submenu] ({})'.format(mkc)
            started=1
            mkc+=1
            count=0
        # print count
        count+=1