Fix ImageMagicK Policy Error

Converting documents from JPG to PDF or vice versa, compressing and scaling images is a relatively common task for me. After installing the required ImageMagick package in Ubuntu, I tried running the convert command but to my surprise, got the following error message:

$ convert source.jpg destination.pdf
convert-im6.q16: attempt to perform an operation not allowed by the security policy `PDF' @ error/constitute.c/IsCoderAuthorized/408.

After little searching I found the resolution as mention below.

Steps to Follow

Open the Terminal on type the command:

$ sudo vim /etc/ImageMagick-6/policy.xml

You will get the output based on the devices attached to you system:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE policymap [
  <!ELEMENT policymap (policy)+>
  <!ATTLIST policymap xmlns CDATA #FIXED ''>
  <!ELEMENT policy EMPTY>
  <!ATTLIST policy xmlns CDATA #FIXED '' domain NMTOKEN #REQUIRED
    name NMTOKEN #IMPLIED pattern CDATA #IMPLIED rights NMTOKEN #IMPLIED
    stealth NMTOKEN #IMPLIED value CDATA #IMPLIED>
]>
<!--
  Configure ImageMagick policies.

  Domains include system, delegate, coder, filter, path, or resource.

  Rights include none, read, write, execute and all.  Use | to combine them,
  for example: "read | write" to permit read from, or write to, a path.
  ......
  Rules are processed in order.  Here we want to restrict ImageMagick to only
  read or write a small subset of proven web-safe image types:

    <policy domain="delegate" rights="none" pattern="*" />
    <policy domain="filter" rights="none" pattern="*" />
    <policy domain="coder" rights="none" pattern="*" />
    <policy domain="coder" rights="read|write" pattern="{GIF,JPEG,PNG,WEBP}" />
-->
<policymap>
  <!-- <policy domain="system" name="shred" value="2"/> -->
  ......
  <policy domain="coder" rights="none" pattern="PS" />
  <policy domain="coder" rights="none" pattern="EPS" />
  <policy domain="coder" rights="read | write" pattern="PDF" />
  <policy domain="coder" rights="none" pattern="XPS" />
</policymap>

The only change is the highlighted line in which none was replaced with read | write and the file was saved. Now running the convert command again worked as expected 👍🏼

Enable/Disable Dell XPS Touchpad with Ubuntu

The first time I purchased Dell's XPS 13 notebook was in 2015 and couldn't be more satisfied. Now I own Dell XPS 13 9380 with Ubuntu 18.04 pre-installed. After initial testing the hardware, I immediately installed a fresh 19.04 and everything was well supported.

However there is no proper was of enabling or disabling the Touchpad. In the Knowledge Base provided by Dell, there is no mention of Ubuntu even though the OS is officially supported. Dell had another link to the Linux issue which didn't look easy to follow. So I am sharing a more simpler fix.

Steps to Follow

Open the Terminal on type the command:

$ xinput list

You will get the output based on the devices attached to you system:

⎡ Virtual core pointer                          id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ ELAN2930:00 04F3:2930                     id=10   [slave  pointer  (2)]
⎜   ↳ Logitech MX Anywhere 2S                   id=21   [slave  pointer  (2)]
⎜   ↳ DELL08AF:00 06CB:76AF Touchpad            id=11   [slave  pointer  (2)]
⎣ Virtual core keyboard                         id=3    [master keyboard (2)]
    ↳ Virtual core XTEST keyboard               id=5    [slave  keyboard (3)]
    ↳ Video Bus                                 id=6    [slave  keyboard (3)]
    ↳ Power Button                              id=7    [slave  keyboard (3)]
    ↳ Sleep Button                              id=8    [slave  keyboard (3)]
    ↳ Integrated_Webcam_HD: Integrate           id=9    [slave  keyboard (3)]
    ↳ Intel HID events                          id=12   [slave  keyboard (3)]
    ↳ Intel HID 5 button array                  id=13   [slave  keyboard (3)]
    ↳ Dell WMI hotkeys                          id=14   [slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard              id=15   [slave  keyboard (3)]
    ↳ Logitech MX Anywhere 2S                   id=22   [slave  keyboard (3)]

For my case DELL08AF:00 06CB:76AF Touchpad id=11 [slave pointer (2)] is line of which is telling me that the Touchpad is using the ID 11, Perfect!

Now all I have to do is to disable this device using the command:

$ xinput --disable 11

Try using the Touchpad and it will not respond. To enable it again:

$ xinput --enable 11

And its done! Just in case you want to get the details of this device, run the command:

$ xinput list-props 11

What if it didn't work?

In that case look for the Knowledge Base I have shared in the start and following those instructions.

How to execute bash script at upstart

In this tutorial, we will learn how to execute a bash script at upstart.

What is Upstart?

Upstart is an event-based replacement for the /sbin/init daemon which handles starting of tasks and services during boot, stopping them during shutdown and supervising them while the system is running.

Commands

Create a Job in /etc/init.

sudo gedit /etc/init/sync_user.conf

Job configuration files are named as <name>.conf

Add the following lines to sync_user.conf

start on filesystem and net-device-up IFACE!=lo
  stop on runlevel [016]

script
  exec bash -c 'path_to_bash_script_file/file_name start'
end script

To ensure that you haven't misused the Upstart syntax, use the init-checkconf command:

init-checkconf sync_user.conf

Then start the job

sudo start sync_user

Understating the code

Start on condition:

start on filesystem and net-device-up IFACE=lo

Job will be started when the filesystem is mounted and net-device-up IFACE=lo event, which signifies the local network (for example, 127.0.0.0 for IPv4) is available.

Stop on conditon:

stop on runlevel [016]

This ensures the job will be stopped on shutdown[0], when switching to single-user mode[1] and on reboot[6].

Runlevels for Debian and Ubuntu systems are generally as follows:

  0 : System halt.
  1 : Single-User mode.
  2 : Graphical multi-user plus networking (DEFAULT)
  3 : Same as "2", but not used.
  4 : Same as "2", but not used.
  5 : Same as "2", but not used.
  6 : System reboot.

Script

All job files must have either an exec or script stanza. This specifies what will be run for the job.

script
  exec bash -c '/opt/local/our-sync-pkg-2.0/sync_users start'
end script

exec gives the path to a binary on the filesystem and optional arguments to pass to it.

Executing bash script

By default, Upstart uses "/bin/sh" to execute script sections. You can change the default shell.

But it can done in simplest way by executing this line:

exec bash -c '/opt/local/our-sync-pkg-2.0/sync_users start'

bashin exec is used because we're executing the bash script.

-c option after bash means that commands are read from string.

end script will terminate the script.

This will work! If you have any suggestions on improving this post, let me know.

Simplest way to create debian package via fpm

Debian Packaging

In this tutorial we will look through how to package some simple hello world script. A quote from debian maintainer's guide:

One thing is certain, though: to properly create and maintain Debian packages takes many hours. Make no mistake, for our system to work the maintainers need to be both technically competent and diligent.

We have many methods to create a Debian package In this tutorial we will use FPM.

VIA FPM

This method requires minimum effort follow this if you don't want to upload to PPA. However it requires ruby gem and package name FPM. check wiki for further details.

mkdir -p ~/via-fpm/debian/usr/bin/
cd ~/via-fpm/debian/
touch ~/via-fpm/debian/usr/bin/hello-via-fpm.sh
gedit ~/via-fpm/debian/usr/bin/hello-via-fpm.sh

Add following lines to script.

#!/bin/bash
echo "hello debian packaging via fpm"

Save and close that file. whatever folder structure you will put in your source folder it will automatically copied into respected folders. There is no need to to copy them. For example if you want to put some sources file in /opt/local/sources then you must have same structure in you application source. Similarly usr/bin/ files will automatically copied to their respected folder in this case that will be /usr/bin.

Next we will come towards the scripts that will automatically run like preinstall , post install , pre un-install and post un-install . If you want to create user, directories, set permissions then these scrips are for you. You can use bash here. In this demo we will use "postinst" script to set permission for ~/via-fpm/debian/usr/bin/hello-via-fpm.sh create postint file in described location and add the following code.

mkdir -p opt/local/
touch opt/local/postinst
gedit opt/local/postinst

Set so that user can execute command from shell.

#!/bin/bash
set -e
sudo chmod +x ~/via-fpm/debian/usr/bin/hello-via-fpm.sh 
exit 0

It't time for packaging.

cd ~/via-fpm
fpm --epoch 1 -s dir -e -C debian \
-a all -m "uncle demo <UncleDemo@example.com>" \
--description "our absurd debian package for demo via fpm" \
-v 1.0  -t deb  -n hello-via-fpm --after-install debian/opt/local/postinst 

Switches that we have used and their meaning

-epoch: Used for epoch value is somehow versioning number
-e: Edit the package spec before building. (default: false)
-C: Change directory to here before searching for files
-a: The architecture name. Usually matches 'uname -m'. For automatic values, you can use '-a all' or '-a: native'. These two strings will be translated into the correct value for your platform and target package type.
-m: The maintainer of this package. (default: "djhaskin987@djhaskin987-S301LA")
--description: add description
-v: specify version number
-t: output type
-n: Name to give to the package
--after-install: file to run after post install

Why FPM:

Because it will automatically create necessary files like control, rules and lot other necessary stuff for you. There are other proper ways to do that using official Debian package management through which you can upload your package to PPA. That we will discuss in next demo.

INSTALLATION:

To install that package either open via Ubuntu software center or run command sudo dpkg -i hello-via-fpm_1.0_all.deb

LAST CHECK:

Now try to run command from shell hello-via-fpm.sh to see that your package is installed now and further you can create your own with customizations.

Installing LibreOffice 5 in Ubuntu

The latest version of LibreOffice is here but unfortunately its not going to be available in Ubuntu 14.04 and 12.04 by default. But the good news is that we can upgrade existing version by typing these commands:

sudo add-apt-repository ppa:libreoffice/ppa
sudo apt-get update && sudo apt-get -y dist-upgrade

That should be enough! :-)

Disable Guest Account in Ubuntu

Ubuntu has a special account, named Guest, which allows access (login) to the system without asking for any password. Although there are limitation applied to this account but maybe its not always desirable to have it. These steps will help in disabling it (tested under 12.04 and 14.04):

Open the file /etc/lightdm/lightdm.conf and add the following line to it at the end:

allow-guest=false

If the file lightdm.conf is missing, then paste the following contents in the blank file:

[SeatDefaults]
allow-guest=false

Once thats done, restart the relevant service:

sudo restart lightdm

This should work!

Installing Ubuntu Updates on Multiple Systems

Today I was installing Ubuntu in my Olives School lab. There are 20 systems in total. After installing it in the first PC, I ran the Update and there were 443 of them which amounted for 337MB approx. As it can be imagined it took some time to get the first PC updated. This was clearly not what I was going to do with the rest and I had to come up with a solution.

When Ubuntu downloads these updates, it places them in /var/cache/apt/archives/ folder. In fact even after installing updates, they are not removed from the system. So a solution was simple:

  1. Copy all the downloaded packages to a USB

  2. On the next PC, run the command:

    sudo cp [path-to-usb]/* /var/cache/apt/archives
  3. Once all the files have been pasted, run the Update Manager tool and it will tell you that updates have been downloaded but not yet installed.

  4. Click on Install :-)

Tool to Manage Ubuntu Services

In an earlier post, I mentioned about the Runlevels in Ubuntu and how its different from the rest of the Linux family. Each Runlevel can be configured to start with certain services. A tool to manage the Services in Ubuntu is sysv-rc-config

This tool can be installed using the command:

sudo apt-get install sysv-rc-conf

Once installed, it can be used as:

sudo sysv-rc-conf

This tool will display all the services and the runlevels. You can easily choose which services to load and which not to. The screenshot shows how it will appear. To exit the tool, press q key.

Install Internet Explorer (IE) on Linux

Although I am not a fan of Internet Explorer but sometimes it cannot be ignored especially when few websites have limited their access to IE browsers only or some old websites with poor markup which only renders on IE.

Internet Explorer (IE 5, 5.5, 6 and 7) can be installed and run on any Linux distribution. The package can be found and downloaded from these links:

  1. http://www.liewcf.com/install-internet-explorer-6-on-linux-2242/
  2. http://www.tatanka.com.br/ies4linux/download.html
  3. http://www.tatanka.com.br/ies4linux/page/Installation
  4. http://webexpose.org/2007/01/07/internet-explorer-7-on-linux/

When installing IEs4Linux, the Linux X-Window may crash, giving you the following error message:

The program ‘ies4linux-gtk.py’ received an X Window System error.
This probably reflects a bug in the program.
The error was ‘RenderBadPicture (invalid Picture parameter)’.
(Details: serial 5546 error_code 158 request_code 148 minor_code 7)
(Note to programmers: normally, X errors are reported asynchronously;
that is, you will receive the error a while after causing it.
To debug your program, run it with the –sync command line
option to change this behavior. You can then get a meaningful
backtrace from your debugger if you break on the gdk_x_error() function.)

The workaround this is to use the non-GUI, command based installation. To install use the command:

./ies4linux --no-gui

For further help:

./ies4linux --help

I hope the day comes when all of this is not required and we have a true cross-browser web.

Join FLV files in Ubuntu

When we download video from Youtube or any other website, 90% chances are you are watching them using Flash Video Player whose format is FLV. Some of the videos uploaded in Youtube are sliced into multiple parts especially when Youtube only allowed you to upload a video of maximum 10 minute duration.

There is a simple but useful way of joining these files into a single under Ubuntu.

First you will need to install the package:

sudo apt-get install avidemux

Next, keeping the audio/video encoding unchanged, just join them (change the filenames accordingly):

mencoder -forceidx -of lavf -oac copy -ovc copy -o output.flv clip1.flv clip2.flv clip3.flv

Google Chrome error – Your preferences can not be Read

Sometimes Google Chrome under Linux or Ubuntu gives the following error:

Your preferences can not be read. Some features may be unavailable and changes to preferences won’t be saved.

This is because the owner of the following files have been changed for some unknown reason: Under /home/[user]/.config/google-chrome/ the file Locale State and under /home/[user]/.config/google-chrome/Default the file Preferences.

Note: This tip works for Linux, for Windows the steps have not been personally tested.

If you are using Windows XP:

C:\Documents and Settings\[Username]\Local Settings\Application Data\Google\Chrome\User Data\Default

If you are using Windows 7:

C:\Users\[Username]\AppData\Local\Google\Chrome\User Data\Default

If you are using Linux:

/home/[Username]/.config/google-chrome/Default

Where user is the supposed name of the user.

To fix the problem, run the following commands (replacing user with the actual username):

sudo chown user:user /home/user/.config/google-chrome/Locale\ State
sudo chown user:user /home/user/.config/google-chrome/Default/Preferences

To fix the permissions in Windows, visit this link: How do I change folder and file Permissions?. Simply deleting the Google folder in the paths specified will also help.

InshAllah the problem will be solved!

Install Apache, PHP and MySQL on Ubuntu

Installing these packages on Ubuntu is very simple. Just execute the following commands and you will be done with everything.

Install Apache

sudo apt-get install apache2

Install PHP

sudo apt-get install php5 libapache2-mod-php5

Install MySQL (with Apache & PHP support)

sudo apt-get install mysql-server libapache2-mod-auth-mysql php5-mysql

Restart Apache

sudo /etc/init.d/apache2 restart

Install MySQL Query Browser

sudo apt-get install mysql-query-browser

Update for MySQL

MySQL has officially declared EOL (End of Life) for Query Browser. You can check it on http://dev.mysql.com/doc/query-browser/en/

MySQL Workbench is its replacement and its now available in Ubuntu 12.04 repositories:

sudo apt-get install mysql-workbench

All features are supported by Workbench. Additionally you can check my answer on askubuntu.com

Move Window Buttons Back to the Right in Ubuntu 10.04

With the release of Ubuntu 10.04, the Window buttons have been moved from the right side to the left. In other words, from Windows way to MAC style.

To get it back to where I was so used to, I found this very helpful post: http://www.howtogeek.com/howto/13535/move-window-buttons-back-to-the-right-in-ubuntu-10.04/

Old is gold!

Mount BIN CUE Images in Ubuntu

Mounting ISO files in Linux is quite straight forward and simple e.g. using the mounter function in Ubuntu straight from the context menu or by using a command line like this:

mount -o loop image.iso /mnt

Anyway mounting BIN/CUE image files is not that straight forward as they’ll need conversion to ISO before mounting, however the process is quite simple, but it need a small application called bchunk. The bchunk package contains a UNIX/C rewrite of the BinChunker program. It converts a CD image in a .bin/.cue format (sometimes .raw/.cue) into a set of .iso and .cdr/.wav tracks. The .bin/.cue format is used by some non-UNIX CD-writing software, but is not supported on most other CD-writing programs.

To install the package:

sudo aptitude install bchunk

In order to convert a bin/cue image set:

bchunk image.bin image.cue image.iso

Then to mount the iso image using this command:

mount -o loop image.iso /mnt

Now you can view the contents in the folder /mnt.

Add RAR and 7-ZIP Support in Ubuntu

Support for RAR and 7-ZIP compressed files can be added to Ubuntu simply by running the following commands:

sudo apt-get update
sudo apt-get install unrar p7zip

Add Google Repositories to Ubuntu (Linux)

Google provides repositories for installing its packages in various Linux distributions. These repositories are automatically added if you simply download, for instance, Google Chrome and install it.

You can visit the following link providing by Google to add the repo using command line also: http://www.google.com/linuxrepositories/

Update and upgrade the package manager after following the mentioned steps.

Change Default GRUB2 Options in Ubuntu 9.10

With Ubuntu 9.10, GRUB 2 is installed by default as the boot loader (although it is still in beta version). The files and commands have been changed.

GRUB 2 settings can be viewed using the command:

sudo gedit /boot/grub/grub.cfg

(You can replace gedit with vim or whichever editor you prefer). This grub.cfg contains the menu entries but it is NOT recommended to change anything in this file. Infact, this file is compiled.

To alter the default menu item, timeout etc, open the grub file using the command:

sudo gedit /etc/default/grub

Make the required changes, for instance in my case I made you changes:

GRUB_DEFAULT=4
GRUB_GFXMODE=1280x800

After making the changes, save the file and compile the output using the command:

sudo update-grub

Reboot and see the results!

Runlevels in Ubuntu

Runlevel is the mode in which the operating system like Linux is running. Conventionally, seven runlevels from 0 to 6 existed. Where 0 meant shutdown and 6 meant Reboot.

In previous versions, Ubuntu used to the /etc/inittab file to manage runlevels, just like most of the Linux distributions. This file was based on traditional init daemon, which is used to perform system startup tasks. This was replaced in Ubuntu 6.10 (Release date: 26th-Oct-2006) with Upstart, an event based daemon. Now there are several files under the /etc/events.d/ directory.

The runlevels that Ubuntu handles by default are:

For more details visit Ubuntu’s Upstart section.

Enable IP Forwarding in Linux

What is IP Forwarding?

Normally, a system can not communicate with another system belonging to a different network address. IP forwarding is the mechanism of forwarding an IP packet from one network (example: 192.168.1.0) to another network (example: 192.168.2.0).

How to enable IP Forwarding in Linux?

By default, IP forwarding is disabled in linux. The current setting can be verfied using the command:

cat /proc/sys/net/ipv4/ip_forward

This will give the output: 0

Another way to test is to run:

sysctl net.ipv4.ip_forward

This will give the output:

net.ipv4.ip_forward = 0

Where 0 means disabled and 1 means enabled.

Enabling IP Forwarding for the Current Running Kernel

Running either of commands will perform the task:

sysctl -w net.ipv4.ip_forward = 1

or

echo 1 > /proc/sys/net/ipv4/ip_forward

But this is only for the current running kernel session. After reboot the old values will be restored.

Permanently Enabling IP Forwarding

Open the required in VIM or any other text editor:

vim /etc/sysctl.conf

Locate the line and modify it as under:

net.ipv4.ip_forward = 1

But these changes will not take effect unless the system is restarted or the command is run:

sysctl -p /etc/sysctll.conf

For Redhat systems, restarting the network service will automatically reload the changes to sysctl.conf:

service network restart

On Ubuntu, this is also possible by restarting the procps service:

/etc/init.d/procps.sh restart

For Debian distributions open the /etc/network/options and make the following changes and restart the network service or reboot:

ip_forward = yes

For Redhat distribution open /etc/sysconfig/network and do the same:

FORWARD_IPV4 = true

The changes can be viewed using the commands mentioned above.