admin System administration

The software sources

Debian GNU/Linux uses the repository methodology to distribute applications. This methodology allows the software centralization and the usage of simple interfaces to administrate and upgrade your system: you have no need to visit the software sites themselves.

The sources.list file

The Internet addresses of the Debian repositories are stored in the /etc/apt/sources.list and the files of the type /etc/apt/sources.list.d/xxx.list.

An example of 'sources.list' file on Debian 9

Details concerning the various information found in the 'sources.list' file (the lines beginning with a "#" are just comments):

  • "deb": means a binary repository (the compiled software itself)
  • "deb-src": means a source repository (the program code files used to compile the software)
  • "http:·...": the Internet address of the repository server
  • "stretch", "stretch/updates": the branch in the repository tree
  • "main": the repository section.

... why "stretch" and not "stable" since the system is based on Debian Stable ??
"stretch" is the precise version name of the installed system. It sets a given version of each packages included in the "stretch" repository (the version of the generic kernel, for example).
"stable" is the generic name of the currently stable.
For the time being, "stretch" is the "stable" version, thus you could used either designation. But when the Debian "stable" version becomes "buster", then "stretch" will change to "oldstable".
Using the precise name of your version allows you to control if and when you want to upgrade your system to the next version, as opposed to some systems which want to impose their upgrades...
For more detailed information, I invite you to visit the dedicated Debian wiki

About repositories, branches and sections/components

Debian organizes its software within repositories. These repositories are divided into branches and sections/components. To learn more about the "testing" and "unstable" branch read the chapter 8.8. One word, however, about the sections/components in the repositories.

There are 3 sections in the official Debian repositories:

section component selection criteria for the packages
main complies to the DFSG without any "non-free" dependency
contrib complies to the DFSG with some "non-free" dependencies
non-free does not comply to the DFSG

DFSG (Debian Free Software Guidelines) : principes du logiciel libre selon Debian (

Only the packages within the main section/component are officially supported by the Debian project and are 100% free software. Rather, those proposed in contrib and non-free are partially or totally non-free.

Having said that, and depending on your type of hardware, it is very possible that some services do not function correctly without using specific (proprietary) drivers. In that case, you need to modify the /etc/apt/sources.list file (details in the following chapter)

Modifying the Repositories

Before you start modifying the software sources of your system, you must be conscious of the risks your are taking by using the "contrib" or "non-free" components of the archived branch.

  • lack of freedom for this king of packages
  • lack of support by the Debian project (you cannot maintain a piece of software without having the source code at your disposal)
  • the contamination of your fully free Debian system.

Now, that you are warned that the non-free people kill the pink rabbits, let's move on:

To modify your software sources, it is enough to edit the 'sources.list' file. Open a terminal in terminal mode (chap.3.8.3), and enter:

apt edit-sources

This command opens the appropriated file with the default text editor (nano or vim). Once you are done with your modifications, save the file ("[Ctrl]+x" with nano, or ":wq" with vim

Example of line entry for the free packages:

deb stable main

Example of line entry for the free packages and the proprietary packages:

deb stable main contrib non-free

Now you can help yourself in the 3 package sections and install the non-free codecs and drivers.

Note also that you can modify your software sources by using the graphical Synaptic package manager (chap.8.3).

APT in a terminal

The following sections present the graphical interface of the APT (Advanced Package Tool) program. This application is also available directly from the command line, allowing a better fine tuning of your system.

This section presents the basic APT commands to manage the Debian packages from a terminal.

Debian supports also "aptitude", another package manager, with a different syntax and behavior. This manual being intended for beginners, no need to explicit these commands here: to learn more about them, visit the dedicated Debian Aptitude Wiki:

'User' command to search and display information

These commands can be executed as simple user, because they do not impact your system.

command description
apt show toto display information about the package toto
apt search toto look for packages corresponding to the toto
apt-cache policy toto display the available version of toto

'Administrator' mode commands for system maintenance

These commands must be executed with the "root" administrator rights, because they impact the system. To move into the administrator mode from a terminal, type "su -": the administrator password is requested.

command description
apt update Update the repositories metadata
apt install toto Install the toto package and its dependencies
apt upgrade Secured update of the installed packages
apt dist-upgrade Update of the installed packet, by adding/removing
other packages if necessary
apt remove xyz Remove the xyz package, but not the configuratrion files
apt-get autoremove Auto remove the unecessary packages
apt purge xyz Purge the xyz package and its configuration files
apt-get clean Clean the local cache of the installed package
apt-get autoclean Clean the local cache of the obsolete packages
apt-mark showmanual Mark a package as being "manually-installed"

For more detailed information and the apt/aptitude equivalence, visit the dedicated page of the Debian manual:

All-in-One command line (in administrator mode) to update the repositories information + update your system + clean the packages in cache:

apt update && apt dist-upgrade && apt-get autoclean

Which goes to show that managing your system with a terminal is not that complex.

Apt vs Apt-get

The Apt program is currently going through some streamlining and offers now a simplified syntax for its commands and options. Thus, you will find both syntax (apt and/or apt-get) in this manual as well as in most of the GNU/Linux documentations.

Backport packages

Debian offers also some special repositories called backports, which contain more recent versions of some applications. These repositories are not activated by default, but do not present any particular risks for your system: the "regular" repositories have the highest priority during the update process, only the applications installed from the backports will look into these specific repositories.

... what do you mean exactly by "backports" ?
Nothing to do, in fact, with the "backdoors" used to spy on your machine running proprietary systems...
The backport is a mechanism allowing an application currently hold in the Debian development repositories, to be ported back to the "stable" version.
For example, the Debian developers take in the development repositories the most recent version of LibreOffice, and re-compile (re-build) the package holding the application, while taking care of all the dependencies existing in the "stable" version.

More details about Backports ine the dedicated page of the Debian wiki ( If you are looking for specific application, you have two solutions: use the search package tool ( [en] or the search by category (

Synaptic: the comprehensive package manager

Synaptic is the comprehensive graphical interface of the Debian package manager. It allows a total vision of the proposed packages, whether installed or not. It is a lot more detailed than the Software Center, or Apper (see the following chapters) since it displays the full set of available packages (including the libraries).

  • Provide the same functionality as apt or apt-get.
  • You need to provide the administrator password to open qand use Synaptic.
  • An active Internet connection is also neede to install or update your software.

Main interface

The Synaptic windows is divided in 4 areas: the tool bar at the top, the left pane allowing different ways of sorting and selecting the packages, the center pane displaying the package list itself, and below the pane hosting the description of the currently selected package (the selection is done with a click).

In front of each package, you notice a little box (white for non-installed packages, green when they are installed, red when they are broken). Next to this status box, a Debian logo indicates that this package is "free" (as in freedom).

Synaptic: the default interface of the package manager

The very first thing to do when you launch Synaptic, is to click on the "Reload" button in order to update all the information (metadata) concerning the repositories, the packages and the available applications.

Don't hesitate to click on all the menus to explore Synaptic and become more familiar with it. It is a good way to discover its numerous functionalities.

Don't be afraid to break your system since nothing will really happen until you click on the "Apply" button. On top of that, a message asking for confirmation will always be displayed first.

Managing the repositories

The repositories allow to update and install additional packages.

Open the Synaptic package manager (menu System > Synaptic package manager)

In the top menu bar, click on "Settings, then "Repositories".

The GNOME desktop repository management uses an explicit "check" interface:

Synaptic: managing sources from Gnome

The management of the repositories on the other desktops like Xfce or LXDE is in "text" mode with the displayed addresses:

Synaptic: managing sources from Xfce

You'll notice that the list corresponds to the contents of the /etc/apt/sources.list file mentioned in chapter 8.1.1.
Now, you can modify your repository sources at your entire convenience. Simply click on a source to modify it, or on the "New" button to add a new source.
Once your modifications are validated, the application will invite you to reload the repositories list in order to take your changes into account.

Note that if you want the "check" interface on Xfce Desktop, you have to install the "software-properties-gtk' package.

Updating the system

Before updating the system, it is necessary to "Reload" the package list, by clicking on the corresponding button, or by going in the menu "Edit > Reload Packages Information" (or even [Ctrl]+r if you want to use a keyboard shortkey). This action checks if the version of the packages residing on your system is the most recent or not.

check repositories informations

Then click on "Mark All Upgrades" or menu "Edit > Mark All Upgrades...".

upgrades request

A new window appears with the list of the packages to be upgraded as well as the additional dependencies, if some are required:

resquest changes list

You only have to click on the "Apply" button, and accept the requested confirmation:

confirm changes

The system updating process begins with the package downloading, and continues with their installation. A message informs you that all the changes were applied.

Synaptic: downloading packages

Synaptic: upgrading packages

system upgraded

Searching for a software

If you don't know the name of the package you need, you can parse the list using the filtering by sections, status, origin, etc ...

By example, if you are looking for a game, click on Sections in the bottom part of the left pane, scroll down to the "Games and Amusement" section, click on it, and the packages concerning games and amusement are listed in the center pane.

If you know the name of the package or if you are looking precisely for something, click on the search button (in the top bar) and enter the keywords of your search in the window which opens.

Other "Custom Filters" are available. Click on the button to explore them.

Look at a package detailed information

By clicking on a package, its description is displayed on the bottom center pane of Synaptic. To obtain even more information on a package, right-click on it, and select Properties, or go to menu "Packages > Properties".

Then you will know everything - positively absolutely everything - on this package; dependencies, installed files, size and version.

Installing / uninstalling softwares

Installing a package

To install one or several packages, right-click on the little box in front of the package name, and select the "Mark for Installation" option.

Synaptic: marking a package for installation

If, in order to be functional, this package requires the installation of other packages (the famous dependencies) they are automatically added to the selection.

Then, you simply need to click on the "Apply" button, and confirm the summary of the changes to be applied.

Synaptic: summary of the pending changes

Synaptic: changes being applied

Synaptic: installation of pacman

Uninstalling a package

Like for the installation, right-click on the little box in front of the package name, and select the "Mark for Removal" option. Then click on "Apply".

The simple removal keep the package configuration files on your system, in case you would like to re-install it, later on.

To remove also the configuration files select the "Mark for Complete Removal" option (equivalent to the "purge" in a terminal command line)

Reinstalling a package

Sometimes we want to re-install a package which is already installed. In that case select the "Mark for Reinstallation" option. This allows, for example, to update the default configuration for the applicatoin if you modified it.

Cleaning useless packages

Often, when software is uninstalled, some packages (the dependencies) remain in the system while no longer useful, since all the packages needing them are gone. These useless packages can be easily removed with Synaptic.

When Synaptic is launched, click on the "Status" button at the bottom of the left pane. If the "Installed (Auto removable)" category shows up, click on it to display the corresponding package(s) (see image below):

Synaptic: auto removable packages

All you have to do next is a right-click on each package in the center pane, and select the "Mark for Complete Removal" option. Once all the packages are marked, click on the "Apply" button.

Removing configuration residues

Although one choose to completely remove a software, some configuration residues might still remain in the system, bur they can be removed with Synaptic.
Click on the "Status" button at the bottom of the left pane. If the category "Not installed (residual config)" shows up, select it (see image below):

Synaptic: removing configuration residues

All you have to do next is a right-click on each package in the center pane, and select the "Mark for Complete Removal" option. Once all the packages are marked, click on the "Apply" button.

Synaptic preferences

"Preferences" is a well-named category, existing in most applications, and which is also present here...
But keep in mind that Synaptic is a very special case: it manages the full set of software installed on your system. When you remove a program, it does not go in the wastebasket (where you could have potentially retrieved it) !

After these scary warnings, let's move to the settings available for Synaptic. the Preferences window (launched via menu Settings > Preferences) displays 6 different tabs:

Synaptic: Preferences window

  • General: the options in there are rather explicit. Note: it is possible to un-tick the option "Consider recommended packages as dependencies", if that helps you keeping an ultra-light system. But this could induce problems when installing future new packages. Thus an option to be handled carefully.
  • Columns and Fonts: allows you to display/mask some columns in the package list, and define the font, if necessary.
  • Colors: you can define here the package colors according to their status.
  • Files: When you install a piece of software, it is first stored in the cache (which is a specific folder of the file system) before being uncompressed and installed. These packages can occupy more and more disk space as you make usage of your computer. Here you can delete them immediately or configure an automatic action.
  • Network: This is the way Synaptic connects to Internet. You should know if your situation requires a modification of these parameters.
  • Distribution: Defines the package upgrade behavior and is very explicit. In case of doubts, do not modify

Remember: by using a terminal (chap.8.2) you can achieve the same results more quickly and with less manipulations.

Discover: the KDE package manager

The Synaptic package manager is the default interface for the software management, but it is sometimes "too" complete. Gnome uses "Software" to manage applications in a simplified way, KDE integrates Discover, an intuitive and efficient software.

Discover simply launched from the KDE main menu > Applications> System > Software Center:

Discover launcher

Discover: default interface

Discover: Manage your applications

Search and install applications from the dedicated search field or by visiting the categories of Discover. A click on the "Install" button is enough:

Searching an application with Discover

Browsing categories with Discover

Install Plasma desktop wisgets directly from Discover by visiting the dedicated category (here with the "Weather" addon):

Installing Plasma modules

Uninstaliing an application with Discover, simply by visiting the "Installed" category then click on "Remove":

Uninstalling with "Discover"

A confirmation will be asked for any action on the software. The process will then be launched in the background. You can follow the progress of the changes from the KDE notification area.

Discover: upgrading your applications

When KDE notifies you of one or more updates, it is "Discover" that launches to perform them:

update notification

Simply click on "Update all" and confirm with the administrator password.

upgrading system on KDE

As with software management, you can follow the process from the KDE notification area.

Software : the simplified package manager

Software is a simplified manager for Debian applications. It allows you to search, install, delete or update packages containing your applications. You can find it in the "System" category of your menus or directly from the Gnome search box by typing "Software".

Software: default Debian interface.

Software: searching an application

Directly from the search magnifying glass button, or by clicking on one of the displayed categories:

Searching an application by its name.

Searching applications through categories.

Software: installing an application

Install an application simply by clicking on its form and then "Install". The administrator password will be requested. You can follow the progress in the main window and then launch directly the newly downloaded application.

Selecting an application for installation.


You can follow installation process.

The installation is successful: you can launch your application directly.

Software: remove an application

Uninstall an application simply by visiting the "Installed" category (at the top of the interface) and clicking on the "Remove" button. You will be asked for confirmation:

Selecting an application for removal.


Software: upgrading your applications

Update your system from the dedicated section "Updates" which will indicate the available and/or already downloaded updates. If no update is available, you can check the repositories using the dedicated button at the top left.
In our example, an update series that includes the "operating system update" requires a reboot. You can list all the updated applications in this batch by clicking on the relevant entry:

updates tab

checking available updates

You then have to restart by clicking on the dedicated button.


reboot to apply updates

Note that for smaller updates, restart is not necessary.

Cleaning the system

Even if the capacity of hard disks increased dramatically during the last years, you might need some free space. Several scripts automate the disk cleaning process, however I must confess that I prefer to check before using the rm command (standing for remove. chap.11.2).

Disk space information

The first thing to do, of course, is to find out the used space on your disk. Several tools are available to you:

Disk space in terminal mode: a summary of the disk space usage for each system mount points (disks and partitions):

df -h

List your folders sorted by decreasing size:

du -ks * | sort -nr

Ncdu: disk space analyzer in console mode. To launch it, simply type "ncdu" in your terminal. To install this software (in administrator mode):

apt update && apt install ncdu

Ncdu launched in the user personal folder

Baobab: disk space analyser in graphic mode, integrated in Gnome.

Baobab: disk space analyzer on Gnome

Fslint: utility to find and clean various forms of unwanted extraneous files in your file system, like duplicates, broken links, empty folders, wrong encoding, etc ... To be manipulated with extreme caution: double check carefully the pending changes before validating the whole process.

Cleaning the packages

Apt/aptitude/dpkg are the usual Debian package managers. When you install a package its archive-source/deb file is stored in your system (in the /var/cache/apt/archives/ folder) to enable a potential re-installation without Internet connection. To clean the "apt cache" use a simple command in administrator mode (chap.3.8.3):

apt-get clean

Once the cache of the installed packages is cleaned, you can also remove the useless packages from your system, as well as the configuration files. Warning! Remember to check carefully the list of the packages planed for removal, before accepting the operation:

apt-get autoremove --purge

Emptying the trash bins

Three different bins must be taken into account:

The user wastebasket : ~/.local/share/Trash/ . You can empty it with the system file manager, or with a terminal:

rm -Rf ~/.local/share/Trash/*

The administrator wastebasket : /root/.local/share/Trash/ . To empty it with the proper manner, use a terminal in administrator mode:

rm -Rf /root/.local/share/Trash/*

The external wastebaskets : locates on your external disks, they are usually named '/media/your_id/your_disk/.Trash_1000', where your_id corresponds to your login name.

Purging application caches

Some applications use a "cache" folder, where they store images, videos, and miscellaneous information in order to run faster. Usually these data do not occupy too much disk space, however if (using the tools described above) you detect that a folder becomes too fat, don't hesitate to remove it.

Each application has its own way to manage its own cache: some purge it systematically when they close, others store their data in the /tmp folder, which will be cleared during the session logout, others keep all their information in a specific folder.

For Firefox, as an example, you can purge the cache from the preferences menu, and even automate this action every time the application is closed.

Purging the thumbnails

Every time you open a folder containing pictures or videos, thumbnails are created to represent these graphic files. These thumbnails are stored in a specific folder to reuse them, rather than being forced to recompute them, every time you access this kind of file.
The problem raised when you delete a graphic file, because its thumbnail is kept in the system, and this leads to a certain amount of disk space used to store obsolete thumbnails.
To purge them, it is enough to remove their corresponding folder:

rm -Rf ~/.thumbnails

This folder will be created again, the next time the system needs to store a newly generated thumbnail.

Installing external ".deb" packages

Debian GNU/Linux uses the package repository system to better manage the software and increase the security of your system. But it may happen that you need an external package of the ".deb" format.

... but who is this "deb" ??
deb is the short for "debian", the mother company. To distribute its software, Debian uses a specific archive file format: ".deb". It is a compressed format, like the ".zip" that you use to save your data. These ".deb" archives are recognized by the different Debian package managers (APT and its graphical interface Synaptic) and thus can be handled more easily.

Installation in graphic mode with gdebi

Gdebi is a graphical utility with allows the installation of external packages of the ".deb" format, while managing the dependencies.

To install it, look for "gdebi" in your favorite package manager (Synaptic, Apper, Packages) or more simply from a terminal in administrator mode using "su" (chap.3.8.3):

apt update && apt install gdebi

When you download a Debian external package, right-click on it and select "Open with gdebi".

Installation in terminal mode with Dpkg

Dpkg is a software utility handling the packages like apt, but it does not manage the dependencies. This means that if you use dpkg to install external packages, you need to install the "dependent" packages one by one from your terminal. Dpkg is integrated in Debian by default, and must be used in administrative mode.

To install an external package:

dpkg -i package.deb

An error message will let you know if some dependencies are missing, an error message will let you know, and then simply install them the classic way with apt:

apt install dependent_1 dependent_2 ...

Then relaunch the installation of your external package:

dpkg -i adresse_du_paquet.deb

To remove an external package:

dpkg --purge package_name

Who is this Sid guy?

First of all, one must know that several Debian distribution branches exist in parallel.

Namely the oldstable, stable, testing and unstable distributions, as well as an experimental branch.

The Stable distribution is the Debian official distribution, the one released at this moment, with is maintained and updated par the Debian teams. The only changes made concern the security updates and the bug fixes. It is recommended to favor this Version.

The Oldstable distribution is the previous stable version. It is usually supported by the Debian teams during one year after the release of the new stable version. Then it might live longer if enough individuals or companies continue to assure its maintenance. Then it is called a LTS (standing for Long Term Support) distribution: we extend its life span.

The Testing distribution is the future Stable version. It is used to prepared the next stable version. When everything is OK, when all the bit and pieces are functioning well together, when all the features targeted by the Debian teams are included, and after a period of software freeze and bug hunting, then the Testing version becomes the official new Stable distribution.

The Unstable distribution, nicknamed Sid is the version which receives all the new packages versions, and sits at the cutting edge of innovation, but is not very stable: it's a research lab. Nevertheless some brave adventurers use it on a daily basis.

The Experimental distribution is not a Debian distribution per se, but rather a repository where alpha or beta software versions are tested.

Toy Story © Disney & Pixar

All these distributions are given a name picked among the characters of the Toy Story® cartoon. Currently, the name of the stable version is Stretch, the name of the testing version is Buster, the name of the oldstable version is Jessie, the Experimental as no nickname.

The name of unstable is Sid, but who is this Sid guy?
Sid is the little boy, in the Toy story® cartoon, who breaks all his toys (

More detailed information on the dedicated Debian Wiki