Howto remap keyboard keys in Linux

Almost two years since I wrote a blog post, but learnt a lot in these past two years. I’ll be writing everything I can remember in the coming days, but first, I need to record down something I learnt recently.

I came across one challenge to generate a key press event where the key is not at all in the normal US keyboard. That special key (Hangul/English Toggle key) is only available in Korean Keyboard. So, here is how I did

We need to choose any one key available in the normal US keyboard and remap it to produce Hangul/English Toggle Key’s code. For my purpose I’m going to remap F7 key to produce Hangul/English keypress events. First, I need to know what F7 produces when it gets pressed. There is a tool called “evtest” which will show the code generated by physical keyboard

Event: time 1496043435.462606, type 4 (EV_MSC), code 4 (MSC_SCAN), value 41
Event: time 1496043435.462606, type 1 (EV_KEY), code 65 (KEY_F7), value 0

Here, the MSC_SCAN value of “41” (hexadecimal) is the code generated by the physical keyboard. Using this value. we need to create one file (/usr/lib/udev/hwdb.d/63-keyboard.hwdb) with the following content

keyboard:name:AT Translated Set 2 keyboard:dmi:*

Here, The first line starting with “keyboard:” indicates the name of the keyboard. There are lot of way to match the keyboard (see /usr/lib/udev/hwdb.d/60-keyboard.hwdb file for more details). The second line which starting with “KEYBOARD_KEY_” should have one space before “KEYBOARD”. The “hangeul” string at the end of the second line is a suffixed lowercase substring of a macro defined in /usr/include/linux/input-event-codes.h file. You can use more than one “KEYBOARD_KEY_=” lines to remap the keys in your physical keyboard.

Once you create the 63-keyboard.hwdb file. Run the following command to update /etc/udev/hwdb.bin file which is used by udev

sudo udevadm hwdb --update

Once the hwdb.bin file updated, Either reboot your machine or trigger udev events for the particular keyboard (here, /dev/input/event1 may vary depend on your keyboard devfile mapping)

sudo udevadm trigger /dev/input/event1

Once you have the remapping, you can test it again with evtest.

Event: time 1496046275.166879, type 4 (EV_MSC), code 4 (MSC_SCAN), value 41
Event: time 1496046275.166879, type 1 (EV_KEY), code 122 (KEY_HANGUEL), value 0

In the above output, MSC_SCAN value “41” generates “KEY_HANGUEL” instead of “KEY_F7”.

Update (2018-02-06):

I recently have to remap Left Window Key to Right Window Key. So I created a new file in /etc/udev/hwdb.d/92-keyboard-override.hwdb and added following lines

# keyboard overrides

# laptop keyboard

# USB keyboard

Here KEYBOARD_KEY_dd=rightmeta changes Menu key to Right Window Key, KEYBOARD_KEY_db=rightmeta and KEYBOARD_KEY_700e3=rightmeta both changes Left Window Key to Right Window Key but former is for laptop keyboard and later is for USB keyboard.

howto change font in linux using fontconfig

To those who are not familier to fontconfig, it is the library which provides fonts to each program in your linux desktop (atleast in gnome3). It maintains the details about all the font files available in your linux box and provides best matched font when your program requests a specific type of font.

If you use only english in day-to-day activities, fontconfig dont come in your way, but its a nightmare if you are a multilingual user. Even if you are a multilingual user, fontconfig tries its best to make your life easy by matching the best font for your language automatically, but the pain starts if you don’t like what fontconfig provides and want to change the default font for your language to something which looks good in the editor.

I went through the pain and want to share what I did to fix. For me, fontconfig said “TAMu_Kadambari” is the best font for “Tamil” and gedit by default shows tamil fonts using “TAMu_Kadambari”. But, this font doesn’t look good in gedit. After much research, I’m able to change the default font for “Tamil” language from “TAMu_Kadambari” to “TAMu_Kalyani” using this xml file.

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<!--save this file as ~/.config/fontconfig/fonts.conf-->
<test name="lang">
<edit name="family" mode="assign">

Here, the <match> tag contains one test which checks if the provided language is “Tamil” (lang=ta). If it is, then edit the original request coming from the application and assign family name as “TAMu_Kalyani”(family=TAMu_Kalyani) so that fontconfig matching algorithm will match only “TAMu_Kalyani”.

Thats it, my gedit now picks “TAMu_Kalyani” and it looks good. More details about fontconfig is available here.

fontconfig uses patterns for its matching algorithm, and it goes like this

<families>-<point sizes>:<name1>=<values1>:<name2>=<values2>..

for example, here is how you can check which is the best matched font available in your system for language “Tamil”. Output also contains top 10 ranked fonts for tamil. The first preferred font is “TAMu_Kalyani”, because I have overridden in ~/.config/fontconfig/fonts.conf

[mohan@mohanlaptop0 ~]$ fc-match -s 'monospace-10:lang=ta' | head
TAMu_Kalyani.ttf: "TAMu_Kalyani" "Regular"
TSCu_Comic.ttf: "TSCu_Comic" "Normal"
DejaVuSans.ttf: "DejaVu Sans" "Book"
DejaVuSansMono.ttf: "DejaVu Sans Mono" "Book"
DejaVuSerif.ttf: "DejaVu Serif" "Book"
Pothana2000.ttf: "Pothana2000" "Pothana2000"
MalOtf.ttf: "MalOtf" "Book"
TSCu_Paranar.ttf: "TSCu_Paranar" "Regular"
SyrCOMAdiabene.otf: "East Syriac Adiabene" "Regular"
SyrCOMKharput.otf: "Serto Kharput" "Regular"
[mohan@mohanlaptop0 ~]$

If I remove ~/.config/fontconfig/fonts.conf, it goes back to the original behaviour and provides “TAMu_Kadambari” as preferred font for “Tamil”

[mohan@mohanlaptop0 ~]$ fc-match -s 'monospace-10:lang=ta' | head
TAMu_Kadampari.ttf: "TAMu_Kadambri" "Regular"
TAMu_Kalyani.ttf: "TAMu_Kalyani" "Regular"
DejaVuSansMono.ttf: "DejaVu Sans Mono" "Book"
DejaVuSansMono-Bold.ttf: "DejaVu Sans Mono" "Bold"
DejaVuSans.ttf: "DejaVu Sans" "Book"
DejaVuSerif.ttf: "DejaVu Serif" "Book"
Pothana2000.ttf: "Pothana2000" "Pothana2000"
MalOtf.ttf: "MalOtf" "Book"
TSCu_Comic.ttf: "TSCu_Comic" "Normal"
TSCu_Paranar.ttf: "TSCu_Paranar" "Regular"
[mohan@mohanlaptop0 ~]$

fontconfig configuration files are very versatile and one can do lot of things, but we need to first understand its patterns to do anything useful. Anyway, I hope this article provide good example for fc-match command-line tool and fontconfig patterns.

SPA (Single Page Application) for amateur web developer

That amateur web developer is none other than “yours truely”.

Recently, I came across this article about a over-engineered blog. It is awesome and gave me insights into React and how client side view-controller frameworks ( like Angular, Ember, Backbone etc.,) works and how modern web developers offloading business logic to client side. The blog post not only inspired me to learn more about these frameworks, it introduced me to what people call SPA (Single Page Application).

After reading about SPA, I cannot control myself to change my personal website into a SPA application. Here I share my experience about the tools I used to develop the new website.

Node.js and Hapi

My previous choice was Node with Express but, this time, I thought I’m not doing anything in the server, its going to be only serving the bytes. So, I decided to use any REST serving framework instead of Generic framework. I came across Restify but decided to go with Hapi for its simplicity (it turned out that I made the right decision)


I don’t use any database in my website and all the contents are fetched from wordpress, google drive and twitter web apis. The website relies heavily on request to connect to these web services and it is one awesome tool to have for a node application which heavily depend on third party web services.

Handlebars, Stylus and Jeet

These are damn good when it comes to view. Handlebars rocks but the built-in helpers are not that helpful, the if block helper not even allow to check for logical operations. I have to write my own helper to do that. Stylus provided the easiest way to design my UI components and Jeet provided the easiest way to create boxes.


 google-code-prettify and jsOnlyLightBox (customized for dynamic picture loading)

Great thing about prettify is, you don’t need to specify the language, it automatically detects and format the pre and code tags. I used jsOnlyLightBox to show pictures in my Gallery. I have customized it for this website because the vennila jsOnlyLightBox requires all the images to be present before we call load(). I did some changes to make it work with dynamically created img tags and it looks simple and elegant.


Socket.IO and Twitter Streaming

Just like my previous website, I used to relay the tweets coming from twitter streams. Integrating twitter streaming with my website took some heavy hours, but the final result is worth for every second I spent.


Browserify and Gulp

I didn’t use any client side javascript frameworks (like Angular, React, Backbone etc.,) but plain javascript classes as node modules. Browserify helped to bundle all the client side modules with ease. Gulp is the one which rendered all the stylus and handlebars files.

What next?

I dont even know whether I did something good or bad. but, compare to previous codebase, the current one is much simplified(without loosing the functionalities) and clean. It was a great learning exprement. But, I bet, I’ll not going to keep this codebase till the next year. If I see another good inspirational article which introduces any latest technologies, then, I’ll jump-in straight. Afterall, no-one is going to care about my personal website except me. The sources are available here. If you want, just take it and tinker yourself.

yield in vala and gio concurrency

By no means, I’m an expert in vala or gio. Infact, I’m just a beginner, but I have learned something while playing with vala which I want to record (for future reference). Here I’ll explain how Gio’s async framework works and how vala uses Gio beneath the tree.

Gio Async Framework:

Better to explain with an example,

Here, I have created a new GObject class called TestGioAsync with something_to_say property. I have implemented a simple async function called test_gio_async_say.  When called, test_gio_async_say will setup GSimpleAsync object, attach another function called test_gio_async_say_idle_func into GMainLoop’s next idle iteration and return.

Once test_gio_async_say_idle_func triggered, it takes the value from something_to_say property and put it into g_simple_async_result_set_op_res_pointer as op_res (which will be picked-up later) and completes the async transaction with g_simple_async_result_complete_in_idle which will call the test_gio_async_say_cb provided in test_gio_async_say in GMainLoop’s next idle iteration.

Once test_gio_async_say_cb triggered, it will call test_gio_async_say_finish which will simply return op_res which contains the value taken from something_to_say property.

Vala Async Framework:

This is the equivalent vala example for the above C example

Vala async functions returns immediately whenever it reaches yield keyword, In this example, I have hooked this.say.callback into GMainLoop’s next idle iteration. In the next idle iteration, this.say will be called and will start execution exactly after the yield statement which will eventually trigger the anonymous lambda function provided in  this.say.begin with sentence as return value.

Once the lambda function triggered, it will call this.say.end which will return the sentence value to the lambda function.

In Vala example, this.say.callback is equivalent to test_gio_async_say_idle_func in C example.

Setup Gnome Development Environment in Archlinux

Many people who want to contribute to Gnome will go with Fedora, because it is the best suitable for gnome developer. But, Archlinux is as good as Fedora in terms of providing latest gnome libraries. Here I’ll explain how I setup my development environment in Archlinux using pacstrap, jhbuild and arch-chroot.

Setup Base

In your home directory, create a folder for gnome and install archlinux packages

$ mkdir -p ~/Devel/gnome/runtime
$ cd ~/Devel/gnome
$ su
# pacstrap -d runtime base base-devel
# chown -R <username>:<groupname> runtime
# exit

Here, <username>:<groupname> must be your username and groupname to make sure you are able to modify the files inside ~/Devel/gnome/runtime without any issues. The above steps will install Archlinux base packages. Now, we need to install jhbuild,


$ cd ~/Devel/gnome/checkout
$ git clone git://
$ cd jhbuild
$ PYTHON=/usr/bin/python2 ./ --prefix="${HOME}/Devel/gnome/runtime/usr"
$ make install

done, next step is to configure jhbuild to setup the paths properly, to do this, we need to copy the sample jhbuildrc file from jhbuild source directory to ~/.config directory and edit that file,

$ cp ~/Devel/gnome/checkout/jhbuild/examples/sample.jhbuildrc ~/.config/jhbuildrc

Here is my .jhbuildrc modifications

# -*- mode: python -*-
--- /home/mohan/Devel/gnome/checkout/jhbuild/examples/sample.jhbuildrc   2015-01-17 11:38:40.055187155 +0800
+++ /home/mohan/.config/jhbuildrc       2015-01-06 09:07:34.493161676 +0800
@@ -10,22 +10,25 @@
 # jhbuild/defaults.jhbuildrc, but can be any file in the modulesets directory
 # or a URL of a module set file on a web server.
 # moduleset = 'gnome-apps-3.12'
+moduleset = 'gnome-world'
 # A list of the modules to build.  Defaults to the GNOME core and tested apps.
 # modules = [ 'meta-gnome-core', 'meta-gnome-apps-tested' ]
 # Or to build the old GNOME 2.32:
 # moduleset = 'gnome2/gnome-2.32'
 # modules = ['meta-gnome-desktop']
+modules = ['gjs', 'farstream', 'gnome-online-accounts', 'polari', 'gnome-shell', 'glade', 'gnome-builder']
 # what directory should the source be checked out to?
-checkoutroot = '~/jhbuild/checkout'
+checkoutroot = '~/Devel/gnome/checkout'
 # the prefix to configure/install modules to (must have write access)
-prefix = '~/jhbuild/install'
+prefix = '~/Devel/gnome/runtime/usr'
 # custom CFLAGS / environment pieces for the build
 # os.environ['CFLAGS'] = '-Wall -g -O0'
+os.environ['PYTHON'] = '/usr/bin/python2'
 # extra arguments to pass to all scripts
 # to speed up builds of GNOME, try '--disable-static --disable-gtk-doc'

Here is the details of my changes,

  • moduleset – A moduleset is an xml file contains details (like modulename, version info, repo address, type of repo, how to build etc.,) of each and every project (we call it as module) needed for gnome environment. jhbuild maintains moduleset for each release, you can see the different modulesets inside your jhbuild directory (~/Devel/gnome/jhbuild/modulesets). “gnome-world” moduleset represent generic set which will be updated for every release. So, I use “gnome-world” to make my environment as latest as possible.
  • modules – when we execute “jhbuild build” command, jhbuild will compile only the modules listed in this place. make sure you build what you want instead of building all the gnome projects (aka “meta-gnome-desktop”)
  • checkoutroot – place where jhbuild will clone the gnome repositories. set this to ~/Devel/gnome/checkout.
  • prefix – place where jhbuild will put the compiled binaries, set this to ~/Devel/gnome/runtime/usr. If you notice, you will see that ~/Devel/gnome/runtime is the same path where we installed archlinux base, so, we basically put the gnome binaries (libraries & executables) on top of archlinux, I’ll tell you why we are doing this when I explain arch-chroot.
  • os.environ[‘PYTHON’] – set this to /usr/bin/python2 because, Archlinux’s default python is python3 but most of gnome modules don’t like python3 (especially jhbuild. see here –


All set, its time to compile.

$ ~/Devel/gnome/runtime/usr/bin/jhbuild build

If jhbuild finds any missing libraries to compile the modules listed in jhbuildrc, it will throw error, here comes the need of arch-chroot.

Installing missing Dependencies

The reason we setup archlinux base in ~/Devel/gnome/runtime is to install any missing libraries here from arch packages using arch-chroot and packman and make sure we don’t distrub the current system. Let say, jhbuild throws that ‘spotread’ is missing when compiling colord module. ‘spotread’ executable is provided by ‘argyllcms’ package and here is the simple way to fix the dependency issue,

$ cd ~/Devel/gnome
$ su
# arch-chroot runtime /usr/bin/bash
# pacman --sync --refresh
# pacman --sync --sysupgrade
# pacman --sync argyllcms
# exit
# chown -R <username>:<groupname> runtime
# exit

Now, we can start compiling again, I suggest to switch to jhbuild environment before we compile, because jhbuild will setup necessary environment variables (like LD_LIBRARY_PATH pointing to ~/Devel/gnome/runtime/usr/lib etc.,) to make sure dependency libraries are resolved from ~/Devel/gnome/runtime/usr.

$ ~/Devel/gnome/runtime/usr/bin/jhbuild shell
$ jhbuild build
$ exit

Now, to execute the latest compiled gnome-builder,  here is the commandline

$ ~/Devel/gnome/runtime/usr/bin/jhbuild run gnome-builder

Thats it, you have your gnome development environment ready.

gistnotes – a gnome shell extension

Well, I should probably say, its basically a gnome application disguised as a shell extension. written entirely using javascript.

Nothing much to say more than what the README say here,


This is my first contribution to gnome. you can install it through Check it out, and provide feedback.

Issue with Sabayon

Long time since I blogged. Life is crazy mate (specially after you become a husband). Personals aside, I have been waiting to blog about my experience with Sabayon.

I was a user of sabyon for about two and half years. But now, I’m a Arch user and thats one damn thing I did right to kickstart my hunger for coding again. Well, sorry sabayon developers, you guys suck!! because you dont worry about your users anymore.

Nothing wrong with the distro (I admire the stability it provided), but your attitude towards the users suck!! everytime we report a bug, you people either say raise this bug to upstream (or) raise this bug in gentoo’s bugzilla because they are the one who create the package.

If gentoo have a package and we ask it to enable it in sabayon overlay, you will say, we don’t enable some package because of one user and one can use gentoo’s overlay if they want. Dammit!! if I want to use gentoo’s overlay, why do I need to install sabayon?

Anyway, goodbye. I’m now in a true rolling distro.