• apt-get : APT is acronym for Advanced Package Tool. It supports installing packages over internet using ftp or http protocols. You can also upgrade all packages in a single operations, which makes it even more attractive. For scripting purpose apt-get is perfect tool.
• dpkg : Debian packaging tool which can be use to install, query, uninstall packages.
• apt : Interactive and recommended command for all users.
• Gui tools: You can also try GUI based or high level interface to the Debian GNU/Linux package system. Following list summaries them:
• aptitude: It is a text-based interface to the Debian GNU/Linux package system.
• synaptic: GUI front end for APT

Red hat Linux package names generally end in .rpm, similarly Debian package names end in .deb, for example:

apache_1.3.31-6_i386.deb

Where,

1. apache : Package name
2. 1.3.31-6 : Version number
3. i386 : Hardware Platform on which this package will run (i386 == intel x86 based system)
4. .deb : Extension that suggest it is a Debian package

Remember, whenever I refer .deb file it signifies complete file name, and whenever I refer package name it must be first part of .deb file. For example, when I refer to a package sudo it means sudo only and not the .deb file i.e. sudo_1.6.7p5-2_i386.deb. You can find out debian package name with the following command:
apt-cache search {package-name}
apt-cache search apache
Finally, most of the actions listed in this post are written with the assumption that they will be executed by the root user running the bash or any other modern shell. Otherwise add sudo command before apt-get:
$ sudo apt-get ....
Ok, let us see some examples.

apt-get add a new package

The syntax is:
apt-get install {package-name}
To install a package called samba, run:
# apt-get install samba
OR
$ sudo apt-get install samba

How do I search for package names?

To find software packages use the apt-cache command:
$ apt-cache search {package-name}
To find vim package list, enter:
$ apt-cache search vim
OR
$ apt-cache search vim | more
OR
$ apt-cache search vim | grep 'word'
You can limit search with regex too. For example, show all vim packages starting with vim word only:
$ apt-cache search ^vim
Sample outputs:

vim - Vi IMproved - enhanced vi editor
vim-common - Vi IMproved - Common files
vim-doc - Vi IMproved - HTML documentation
vim-gnome - Vi IMproved - enhanced vi editor (dummy package)
vim-gtk3 - Vi IMproved - enhanced vi editor - with GTK3 GUI
vim-gui-common - Vi IMproved - Common GUI files
....
..
...
vim-vimerl - Erlang plugin for Vim
vim-vimerl-syntax - Erlang syntax for Vim
vim-vimoutliner - script for building an outline editor on top of Vim
vim-voom - Vim two-pane outliner
vim-youcompleteme - fast, as-you-type, fuzzy-search code completion engine for Vim

apt-get remove the package called samba but keep the configuration files

The syntax is:
apt-get remove {package-name}
For example to remove a package named samba, run:
# apt-get remove samba

apt-get remove (erase) package and configuration files too

The syntax is:
apt-get --purge remove {package-name}
For example, delete a package named samba including config files stored in /etc/ directory:
# apt-get --purge remove samba

How do I remove packages that were automatically installed to satisfy dependencies for other packages and are now no longer needed?

Run the following command:
$ sudo apt-get autoremove
OR
$ sudo apt-get --purge autoremove
The above command is quite useful to remove unwanted kernel on a Debian or Ubuntu Linux.

How do I update my system?

The syntax is:
# apt-get update
# apt-get upgrade
To upgrade individual package called sudo or bash, enter:
# apt-get install sudo
# apt-get install bash
Sample outputs:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Suggested packages:
  bash-doc
Recommended packages:
  bash-completion
The following packages will be upgraded:
  bash
1 upgraded, 0 newly installed, 0 to remove and 7 not upgraded.
Need to get 1427 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://cdn-fastly.deb.debian.org/debian stretch/main amd64 bash amd64 4.4-4+b2 [1427 kB]
Fetched 1427 kB in 2s (661 kB/s)
debconf: delaying package configuration, since apt-utils is not installed
(Reading database ... 8417 files and directories currently installed.)
Preparing to unpack .../bash_4.4-4+b2_amd64.deb ...
Unpacking bash (4.4-4+b2) over (4.4-4+b1) ...
Setting up bash (4.4-4+b2) ...

apt-get display available software updates

Type the following command to display the list of all available upgrades (updates) using -u option
# apt-get update
# apt-get -u upgrade
Sample outputs:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
  apt bash gcc-6-base init init-system-helpers libapt-pkg5.0 libgcc1 libstdc++6
8 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 4244 kB of archives.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n]

If you decided to upgrade all of the shown packages just hit ‘y’ key. If you just want to see a list, enter:
# apt-get -u upgrade --assume-no
However, if you just wish to upgrade individual package then use apt-get command and it will take care of rest of your worries:
# apt-get install {package-name}

How do I upgrade my Debian or Ubuntu Linux distro?

From the man page:

The dist-upgrade option to apt-get 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. The dist-upgrade command may therefore remove some packages.

This is useful to upgrade your distro including kernel:
$ sudo apt-get update
$ sudo apt-get dist-upgrade

dpkg command to get package information such as description of package, version etc.

The syntax is:
dpkg --info {.deb-package-name}
For example:
$ dpkg --info sudo_1.6.7p5-2_i386.deb | less

List all installed packages

The syntax is:
dpkg -l
Example:
$ dpkg -l

How do I list individual package such as apache or sudo

$ dpkg -l apache
Sample outputs:

Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                                  Version                 Architecture            Description
+++-=====================================-=======================-=======================-===============================================================================
ii  sudo                                  1.8.19p1-1ubuntu1       amd64                   Provide limited super user privileges to specific users

You can also use this command to see (verify) if package sudo is installed or not (note that if package is installed then it displays package name along with small description):
$ dpkg -l | grep -i 'sudo'
To list packages related to the apache:
$ dpkg -l '*apache*'
List files provided (or owned) by the installed package (for example what files are provided by the installed samba package). The syntax is:
dpkg -L {package-name}
For example:
$ dpkg -L samba
$ dpkg -L sudo
Sample outputs:

/.
/etc
/etc/pam.d
/etc/pam.d/sudo
/etc/sudoers
/etc/sudoers.d
/etc/sudoers.d/README
/lib
/lib/systemd
/lib/systemd/system
/usr
/usr/bin
....
..
...
/var/run
/usr/bin/sudoedit
/usr/lib/sudo/libsudo_util.so
/usr/lib/sudo/libsudo_util.so.0
/usr/share/man/man8/sudoedit.8.gz

To list files provided (or owned) by the package (for example what files are provided by the uninstalled sudo package). The syntax is:
dpkg --contents {.deb-package-name}
For example:
# dpkg --contents sudo_1.6.7p5-2_i386.deb

Find out what package owns the file /bin/netstat?

The syntax is:
dpkg -S {/path/to/file}
For example:
$ dpkg -S /bin/netstat
Sample outputs:

net-tools: /bin/netstat

So net-tools package provided /bin/netstat command.

How do I search for package or package description?

Some times you don’t know package name but aware of some keywords to search the package. Once you got package name you can install it using apt-get -i {package-name} command:
apt-cache search "Text-to-search"
apt-cache search "httpd"
apt-cache search "web server"
apt-cache search "web server"| grep something


Find out all the Debian package which can be used for intrusion detection

Type the following command:
code>$ apt-cache search "Intrusion Detection"

Find out all sniffer packages, run:

$ apt-cache search sniffer

Find out if Debian package is installed or not (status)

The syntax is:
dpkg -s {package-name} | grep Status
For example:
$ dpkg -s samba| grep Status

How do I list each dependency a package has…

Display a listing of each dependency a package has and all the possible other packages that can fulfill that dependency. You hardly use this command as apt-get does decent job fulfill all package dependencies. The syntax is:
apt-cache depends package
To display dependencies for lsof and mysql-server packages:
$ apt-cache depends mysql-server
$ apt-cache depends lsof
Sample outputs:

lsof
  Depends: libc6
  Depends: libselinux1
  Suggests: perl

Further reading

• Our dpkg cheat sheet
• Our apt-get cheat-sheet
• Ubuntu / Debian Linux apt Command Examples