Linux – Edit Software Package Source File

You use the following command on a Linux machine to install software packages:

sudo apt-get install <package-name>

Or you use some GUI-based tool for example the “Software Center” on Ubuntu if you have installed a desktop environment on your machine.

In any case, the machine needs to know where to look for packages to install them.

On Linux Debian Jessie or Ubuntu 16.04 Desktop, the path is,

/etc/apt/sources.list

The file sources.list stores all the sources that the machine is supposed to look in when you command the machine to install new software packages. The file on my Debian test machine looks like the following:

 #

# deb cdrom:[Debian GNU/Linux 8.7.1 _Jessie_ - Official amd64 DVD Binary-1 20170116-11:01]/ jessie contrib main

deb cdrom:[Debian GNU/Linux 8.7.1 _Jessie_ - Official amd64 DVD Binary-1 20170116-11:01]/ jessie contrib main

deb http://ftp.de.debian.org/debian/ jessie main
deb-src http://ftp.de.debian.org/debian/ jessie main

deb http://security.debian.org/ jessie/updates main contrib
deb-src http://security.debian.org/ jessie/updates main contrib

# jessie-updates, previously known as 'volatile'
deb http://ftp.de.debian.org/debian/ jessie-updates main contrib
deb-src http://ftp.de.debian.org/debian/ jessie-updates main contrib

You can open this file with any text editor installed on your machine. On Debian Jessie, you can find the text editor “leafpad” pre-installed on the machine.

The following shows the same file but this time from an Ubuntu 16.04 machine:

 #deb cdrom:[Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2)]/ xenial main restricted

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://de.archive.ubuntu.com/ubuntu/ xenial main restricted
# deb-src http://de.archive.ubuntu.com/ubuntu/ xenial main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://de.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
# deb-src http://de.archive.ubuntu.com/ubuntu/ xenial-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://de.archive.ubuntu.com/ubuntu/ xenial universe
# deb-src http://de.archive.ubuntu.com/ubuntu/ xenial universe
deb http://de.archive.ubuntu.com/ubuntu/ xenial-updates universe
# deb-src http://de.archive.ubuntu.com/ubuntu/ xenial-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://de.archive.ubuntu.com/ubuntu/ xenial multiverse
# deb-src http://de.archive.ubuntu.com/ubuntu/ xenial multiverse
deb http://de.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
# deb-src http://de.archive.ubuntu.com/ubuntu/ xenial-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://de.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
# deb-src http://de.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu xenial partner
# deb-src http://archive.canonical.com/ubuntu xenial partner

deb http://security.ubuntu.com/ubuntu xenial-security main restricted
# deb-src http://security.ubuntu.com/ubuntu xenial-security main restricted
deb http://security.ubuntu.com/ubuntu xenial-security universe
# deb-src http://security.ubuntu.com/ubuntu xenial-security universe
deb http://security.ubuntu.com/ubuntu xenial-security multiverse
# deb-src http://security.ubuntu.com/ubuntu xenial-security multiverse

Let’s take a look at a sample line from the code above:

 deb cdrom:[Debian GNU/Linux 8.7.1 _Jessie_ - Official amd64 DVD Binary-1 20170116-11:01]/ jessie contrib main
  • This line starts with “deb”. It corresponds to binary packages that you can install with “apt”.
  • If you take a look at any of the files above, you’ll find lines starting with “deb-src”. Those lines correspond to source packages that you need to download first, compile yourself and then install.

The next part in the line above is the source:

cdrom:[Debian GNU/Linux 8.7.1 _Jessie_ - Official amd64 DVD Binary-1 20170116-11:01]/
  • Here you could find “cdrom”, “http”, “ftp” or “file” if you have a local repository.
  • In this case, the system has listed the install cd-rom with which the operating was first installed.

The next part in the main line above is the distribution name:

jessie

The next part in the main line above identifies what sort of packages you’re interested in:

contrib main

You could have the keywords “main”, “contrib”, “non-free”, “stable”, “unstable”, etc. Which one of these you should use depends on what you want to do. You usually find such information from the source whenever you need them. It’s not required to know them all by heart but just to understand their meaning or concept.

Linux: Upgrading Installed Software Packages

In order to update the software packages installed on your Linux machine, there are mainly the following two options:

sudo apt-get upgrade
sudo apt-get dist-upgrade

Here’s an excerpt from “man apt-get”:

upgrade is used to install the newest versions of all packages
    currently installed on the system from the sources enumerated in
    /etc/apt/sources.list. Packages currently installed with new
    versions available are retrieved and upgraded; under no
    circumstances are currently installed packages removed, or packages
    not already installed retrieved and installed. New versions of
    currently installed packages that cannot be upgraded without
    changing the install status of another package will be left at
    their current version. An update must be performed first so that
    apt-get knows that new versions of packages are available.
dist-upgrade in addition to performing the function of upgrade,
    also intelligently handles changing dependencies with new versions
    of packages; apt-get has a "smart" conflict resolution system, and
    it will attempt to upgrade the most important packages at the
    expense of less important ones if necessary. So, dist-upgrade
    command may remove some packages. The /etc/apt/sources.list file
    contains a list of locations from which to retrieve desired package
    files. See also apt_preferences(5) for a mechanism for overriding
    the general settings for individual packages.

As you can see, “upgrade” is safe as it will abort if there are dependency issues while upgrading packages.

“dist-upgrade” takes care of dependency issues as well and upgrades them as well if it’s required.

Normally you should use “upgrade”. If “upgrade” doesn’t work, you can go through the list of dependency issues and decide whether you can upgrade them as well or not. There might be instances where you simply cannot upgrade a package. For example, you want to upgrade all packages on your machine. You use the first command. Some of the packages go through but a few remain untouched since there are dependency issues. You go through the dependencies of one of them and find out that if you upgrade one of those dependencies, then another program on your machine won’t work. In such circumstances, it’s basically not possible to upgrade and you need to find another solution.

It’s always advisable to have a test machine and run your updates on the test machine first before running them on your production machine. Virtual machines help you do this easily by enabling you to create an exact image of your main machine on which you can test your updates.

Linux – Updating the Software Packages Index

You Linux box installs software from certain repositories. Those repositories are linked to from the operating system and so the system knows where to look for for packages to install.

If you try to install the Apache web server, for example, on your machine, chances are that the machine knows that it has the package on the install DVDs that came with the operating system. If that’s the case, the system asks you to insert that specific DVD to get the package and install it.

But basically, whatever you install on the system comes from an online repository most of the time. The system could have links to, say, 5 online repositories by default. You could add your own repositories as well.

The system makes a list of all the software packages that are available at all those repositories and keeps that list locally on the machine. The next time you want to install something, the system knows from where to download the package.

The list we were talking about gets updated by repository maintainers. Whoever is in charge of those repositories is supposed to make sure that the software is safe, clean and up-to-date. So they have to change their index from time to time. When the repository changes their index, your machine doesn’t get notified automatically. So you need to update you own local index manually from time to time, basically, almost whenever you want to install new software packages. The following command will get exactly that done for you.

sudo apt-get update

Linux – Installing and Uninstalling Packages

In Linux, you install software packages in a few different ways. First off, let me tell you what I mean by “software packages”. A software package in Linux is simply a program that you install on you Linux box to do something specific for you.

For example, you want to install an HTTP server on your machine so that clients can get HTML documents in the form of websites from your machine. One way to do that is to install the Apache HTTP server and that would be a software package or simply a “package” that you install on your Linux box.

Installing Software Packages

You can use any of the following ways to install software packages on a Linux machine.

Compile from the Source Code Yourself

On a Linux machine, one way to install a web server is to get the source package distributed by The Apache Software Foundation, compile it yourself and install it. You usually do this if the other option described here is not good enough for you. We’ll cover this option later.

In this guide, we’re not going to talk about compiling software. We’re going to talk about how you could get software from your own repository.

Download and Install from Your Repository (Command Line)

Every Linux distribution, for example Ubuntu, has its own software repository. There, you can find the compiled version of most software packages that have been compiled specifically for that specific distribution. To do this, you usually use the command

sudo apt-get install <package-name>

in a command interface on the machine and the package will automatically be downloaded and installed on your machine. If you don’t understand the command used here, it’ll be explained later in this guide. The problem with this option could be that you would not have any control over the software version since you usually don’t maintain the software repository. When you run this command, chances are, you’ll automatically get the latest version of the software available in the repository, not the latest version of that software available at any given time.

Use the Graphical User Interface (GUI)

Every Linux distribution has a desktop environment that gets installed along with the operating system (if you wish to). For example, if you install Ubuntu with the desktop environment and GUI by default, you’ll have access to “Software Center”. Using the Software Center, you can use a GUI to search for the packages you need and install them rather than using a command line interface. Please note that in this case, the packages are downloaded from the software repositories maintained for Ubuntu.

Installing Software Packages from the Command Line

For the sake of this guide, let’s say you’re installing the Apache web server. You’d simply enter the following command in a command line interface on you machine:

sudo apt-get install apache2

“sudo” here refers to “Super User”. You use that whenever you want to exercise you administrative rights on the system. For example in this case, since you’re installing software on the system, you do need that. You need to be a super user on the machine, otherwise you’re not allowed to install software on the machine.

The part that says “apt-get install” is used whenever you’re installing software.

“apache2” is the name of the web server software package.

Once you enter this command, you might be asked to enter your password and the package will be installed.

Un-installing Software Packages

In order to un-install software packages, you either use the command line interface or the GUI that comes with your Linux distribution.

Using the GUI is simple. You just find the software package installed and then you’ll have some button that lets you un-install the package.

Using the command line interface, you’ll have more control over what happens behind the scenes since you can define the following:

Un-install But Keep the Configuration

the package is un-installed but the settings related to the application remain on the machine. If you decide to install the package at a later time, you won’t have to reconfigure it anymore. You could use your old settings. In this case use the following command:

sudo apt-get remove <package-name>

Un-install and Purge the Configuration

If you decide not to keep the configuration files and data, use the following command:

sudo apt-get purge <package-name>

Un-install and Delete the Packages from the Archive

When you install a package, the package is first downloaded and saved to some folder on your machine. For example, if you use Debian Jessie, it could be the path /var/cache/apt/archives.

When you un-install the package, no matter which one of the above methods you decide to use, the package itself remains on you machine in the path above for example. If you want to delete the package from this path as well, for example to save some disk space, you need to use the following command:

sudo apt-get clean <package-name>

Un-install Dependencies as Well

When you install a package, there are probably many more packages that are called the “dependencies” of the package that you want to install. Those dependencies are also installed along with the main package. If you’re installing the package on a command line interface, the system reports all the dependency packages as well.

Now, when you un-install the main package later (from a command line interface), the system reports all the packages that are no longer needed to be installed on the system since they were the dependencies of the package you’re trying to un-install. If you decide to un-install those dependency packages as well, you can use the following command:

sudo apt-get autoremove

Checking the List of Installed Software Packages

Use the following command to see a list of all installed software packages on the machine.

dpkg --list

Installing Sofware Packages in Linux from the Command Line Interface

To install any software package from the command line interface in Linux, you need to have Super User rights first. That means, you are either logged in as the “root” user or you’re not “root” but your username in the system is a Super User. Once you’ve taken care of this, you can open a terminal on your machine and type the following command:

sudo apt-get install <package-name>

If you’re installing the Apache HTTP web server for instance, the command would be,

sudo apt-get install apache2
  • “apt-get install” is used in case of installing software packages in general.
  • “apache2” is the name of the the package in your repository. These names are usually the same in case of different Linux distributions but you usually can find out what the name is if you do a simple Google search or read your distribution’s documentation.

A repository is basically a place on the Internet where all such software packages are kept and maintained for your specific distribution of Linux. They build the application from the source code that they get from the software vendor, compile it specifically for your distribution and then keep it in the repository. Once you run the command mentioned above, the package will be downloaded from the repository and installed on the machine.

Sometimes, the software is on the DVD with which you installed the operating system. Especially in case of Debian, the installation media is way too big and contains almost everything, in terms of those software packages, that you might need. When you install the operating system, the system asks you to let the system scan all the media that you currently own related to the operating system and keeps a record of them. The operating system knows which package can be found on which media. For example, in case of Debian, the apache2 package is on the first DVD. So then if run the command mentioned above, the machine asks you to insert the first DVD and installs the software from the DVD rather than going to the Internet and downloading the package. It’s worth mentioning that when you want to install Debian, you don’t have to install all the DVDs that you find on Debian.org and scan them all during the installation. The first one is enough. If you need anything else in the future, you could always go out to the Internet and download it.

Now when you run the command mentioned above, the following happens and is prompted to you in the terminal:

  • The system will read the package lists to make sure that it has the package you’re looking for. “Reading package lists… Done”
  • The system builds the dependency tree. This is a list of all the packages that are required for the package you’re trying to install. That means, the installation of your desired package depends on the existence of those dependency packages. If they’re not already present, they’ll be installed too.  “Building dependency tree”
  • “Reading state information… Done”
  • The system will inform you about the extra packages that need to be installed. “The following extra packages will be installed: <list-of-extra-packages>”
  • The system suggests some other packages that are usually installed along with the package you’re trying to install, or a list of packages that somehow go well with the desired package. For example, if you’re installing some sort of virtualization software, the system will suggest that you install the management console related to that software package as well so that you can manage it easily on a GUI. “Suggested packages: <list-of-suggested-packages>
  • The system will give you an overall report of what’s going to happen, for example how many packages are going to be upgraded, how many removed, how many installed, etc. “0 upgraded, 10 newly installed, 0 to remove and 0 not upgraded”
  • The system will inform you about the size of the packages that it needs to get. “Need to get 0 B/1,942 kB of archives.”
  • The system will inform you about the additional disk space required for the whole operation. “After this operation, 6,643 kB of additional disk space will be used.”
  • The system will ask you if you want to continue. “Do you want to continue=[Y/n]”
  • Once you say, “Yes”, the system will ask you to insert the disk that came with the operating system, if you have scanned that disk before while you were installing the operating system. This way, you don’t have to download anything from the Internet. “Media change: please insert the disk labeled ‘Debian GNU/Linux 8.7.1 _Jessie_  – official amd64 DVD Binary-1 20170116-11:01’ in the drive ‘/media/cdrom/’ and press enter”
  • Once you insert the disk, the system will start to get the relevant packages from the DVD, unpack them and install them. Everything will be reported as it’s being done. You can always scroll up in your terminal to read about everything that happened during the installation. And your package is installed.

How to Find Out What Linux Desktop Environment You Are Using

In a terminal console type the following code:

env | grep DESKTOP_SESSION

If you’re using LXDE for example, you’ll get the following back:

DESKTOP_SESSION=LXDE

Or you can list all the files/directories in the following path:

ls /usr/bin/*session

If you’re running an LXDE desktop under Debian 8.7.1 for example, the ls command will find the executable file “lxsession” for you in the path. That shows that you’re running an LXDE desktop for example.

How To: Write Compile Run a C Program on Ubuntu

There are many Integrated Development Environments (IDEs) no matter what platform you’re on, Window, Linux, Max OS, Unix, etc. You can install  and configure them and develop software projects in them. For example, you could install Codeblocks, Netbeans, any IDE from Eclipse and the list goes on.

This guide comes in handy if,

  • you want to write a simple small program on a Linux machine for example to test something
  • you want to understand how the compilation or execution process works when you write a program or project in an IDE and run it.

So to write a simple “Hello World” Program in C language on an Ubuntu machine, you can proceed as follows:

Open gedit, write your program code in it and save your program somewhere you can find it. “gedit” is the standard text editor that you can find on almost all the different types of Linux machines like Ubuntu, Mint, etc.

You code might look something like this:

#include <stdio.h>
int main() {  
printf("Hello world!");
return 0; 
}

Save this files as hello.c somewhere you can navigate to using your Terminal (We’ll get to this in a little bit). This is just your source code and needs to be translated into machine code so that the machine can understand it and so you can run it.

In order to translate the source code into machine code, you use the C compiler that comes pre-installed on Ubuntu called GCC short for GNU Compiler Collection.

Now in order to compile the code, open a terminal window like “Terminal” on an Ubuntu machine. In Terminal, go to the path you saved hello.c. You should be able to do that by using commands like “pwd”, “cd”, etc to navigate to the path you saved hello.c. I’m assuming you can find your way through your file system on a terminal on your Linux machine. If not, Google for example, “Ten most important Linux commands” and you will be able to learn your way through.

Once you’re inside the path where you saved the file, write the following to compile your source code using GCC:

gcc hello.c -o helloWorld

“gcc” is the name of your compiler. “hello.c” is the source code. “-o” implies output and “helloWorld” is the name of the executable file that the compiler is going to create from your source code.

After successful compilation, you’ll have the file “helloWorld” in the same directory where you save hello.c. You could check that if you used the command “ls” for example which would give you a list of files present in the directory you were currently in.

Then, assuming that you’re still in the same directory where you saved hello.c, you can now run helloWorld right from the terminal.

./helloWorld

As a result the sentence “Hello World!” will be printed in the terminal which is what you used as the argument for the printf function in your program.

As a final note, in Linux, everything is case sensitive. So be careful about your naming conventions. That means, “helloWorld” is NOT the same files as “helloworld”.

Get a List of Commands in Linux From the System

If you want to have a list of all commands that you can use on a Linux machine, try one of the following:

compgen -b

gives you a list of built-in commands.

compgen-c

gives you a list of all commands.

Since the lists are long, you need to use | more at the end of each command to be able to go through the list easily, like the following,

compgen-c | more