View source for Ubuntu package

= Package maintenance =
* https://help.ubuntu.com/community/AptGet/Howto#Maintenance_commands
* [http://www.tecmint.com/useful-basic-commands-of-apt-get-and-apt-cache-for-package-management/ 25 Useful Basic Commands of APT-GET and APT-CACHE for Package Management]
* [http://askubuntu.com/questions/766823/apt-get-being-replaced-with-apt apt-get being replaced with apt? in Ubuntu 16.04] '''apt''' now comes with a progress bar, coloring, etc.

= Security of deb packages =
[https://www.makeuseof.com/how-deb-packages-are-backdoored-how-to-detect-it/ How DEB Packages Are Backdoored and How to Detect It]

= [https://en.wikipedia.org/wiki/Wajig wajig]: Simplyfying Debian Administration =
* [https://linoxide.com/tools/wajig-package-management-debian/ Wajig - Unified Package Management Front-end for Debian]
* [https://unix.stackexchange.com/questions/767/what-is-the-real-difference-between-apt-get-and-aptitude-how-about-wajig What is the real difference between “apt-get” and “aptitude”? (How about “wajig”?)]
** wajig listfiles foo 
** wajig whichpkg /usr/bin/foo
* Examples
** [https://rattle.togaware.com/rattle-install-ubuntu.html Install Rattle] on Ubuntu

= GNOME software =
* https://en.wikipedia.org/wiki/GNOME_Software
* [https://technastic.com/gnome-software-center-on-chrome-os/ How to Install GNOME Software Center on Chrome OS]
* When I use GNOME software to install "okular", the application is not found in the regular path? When I use it to open a pdf file, I see a new process "bwrap --args 36 okular XXX.pdf".

= nala =
* https://gitlab.com/volian/nala, https://github.com/volitank/nala
* [https://ostechnix.com/nala-commandline-frontend-for-apt/ Nala – A Feature-rich Commandline Frontend For APT Package Manager]. Nala ships with the following distinct features out of the box.
** Pretty output formatting,
** History function,
** Parallel downloads,
** Fetch fastest mirror.
* [https://trendoceans.com/nala-package-manager/ Nala: A Beautiful and Structured Frontend for the APT Command]

= Package repository and /etc/apt/sources.list =
* https://help.ubuntu.com/community/Repositories/CommandLine
* http://askubuntu.com/questions/197564/how-do-i-add-a-line-to-my-etc-apt-sources-list
<syntaxhighlight lang='bash'>
echo "new line of text" | sudo tee -a /etc/apt/sources.list
# OR
# use 'add-apt-repository' command 
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 886DDD89
sudo add-apt-repository "deb http://deb.torproject.org/torproject.org $(lsb_release -s -c) main"
sudo apt-get update
</syntaxhighlight>

* https://www.digitalocean.com/community/tutorials/how-to-set-up-r-on-ubuntu-14-04
<syntaxhighlight lang='bash'>
sudo sh -c 'echo "deb http://cran.rstudio.com/bin/linux/ubuntu trusty/" >> /etc/apt/sources.list'
# Or the following if the OS is Ubuntu 
# (other derived distributions like Linux Mint do not count)
# because $(lsb_release -s -c) returns the CodeName which diffs from each Linux distributions.
# sudo sh -c 'echo "deb http://cran.rstudio.com/bin/linux/ubuntu $(lsb_release -s -c)/" >> /etc/apt/sources.list' 

gpg --keyserver keyserver.ubuntu.com --recv-key E084DAB9
gpg -a --export E084DAB9 | sudo apt-key add -
sudo apt-get update
sudo apt-get -y install r-base
</syntaxhighlight>

== sources.list.d ==
This directory has more contents than the /etc/apt/sources.list file. For example, on my Mint 17.2
<syntaxhighlight lang='bash'>
$ cat /etc/apt/sources.list
#deb cdrom:[Linux Mint 17.2 _Rafaela_ - Release amd64 20150627]/ trusty contrib main non-free
deb http://download.virtualbox.org/virtualbox/debian trusty contrib
$ ls /etc/apt/sources.list.d
additional-repositories.list  google-chrome.list                   shutter-ppa-trusty.list
docker.list                   mc3man-mpv-tests-trusty.list         stebbins-handbrake-releases-trusty.list
ekozincew-ppa-trusty.list     official-package-repositories.list   webupd8team-java-trusty.list
getdeb.list                   openshot_developers-ppa-trusty.list  wine-wine-builds-trusty.list
</syntaxhighlight>

See an example of how to use it: https://apt.syncthing.net/
<syntaxhighlight lang='bash'>
# Add the release PGP keys:
curl -s https://syncthing.net/release-key.txt | sudo apt-key add -

# Add the "stable" channel to your APT sources:
echo "deb https://apt.syncthing.net/ syncthing stable" | sudo tee /etc/apt/sources.list.d/syncthing.list

# Update and install syncthing:
sudo apt-get update
sudo apt-get install syncthing
</syntaxhighlight>

== GPG ==
A Practical Guide to GPG. 
* [https://www.linuxbabe.com/security/a-practical-guide-to-gpg-part-1-generate-your-keypair Part 1 Generate Your Keypair], 
* [https://www.linuxbabe.com/security/a-pratical-gpg-guide-part-2-encrypt-and-decrypt-message Part 2 Encrypt and Decrypt Message], 
* [https://www.linuxbabe.com/security/a-practical-guide-to-gpg-part-3-working-with-public-key Part 3 Working with Public Key], 
* [https://www.linuxbabe.com/security/a-practical-guide-to-gpg-part-4-digital-signature Part 4 Digital Signature].

{{Pre}}
$ sudo apt update  # today is 10/22/2020

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://cloud.r-project.org/bin/linux/ubuntu focal-cran40/ InRelease: The following signatures were invalid: EXPKEYSIG 51716619E084DAB9 Michael Rutter <marutter@gmail.com>
...
</pre>

[https://askubuntu.com/a/291095 How to add a GPG key to the apt sources keyring?]
<pre>
wget -qO - https://deb.opera.com/archive.key | sudo apt-key add -

$ apt-key list
/etc/apt/trusted.gpg
--------------------
...
pub   rsa2048 2010-10-19 [SCA] [expired: 2020-10-16]
      E298 A3A8 25C0 D65D FD57  CBB6 5171 6619 E084 DAB9
uid           [ expired] Michael Rutter <marutter@gmail.com>
...
</pre>

The solution is to run the '''sudo apt-key''' again.
{{Pre}}
$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys E298A3A825C0D65DFD57CBB651716619E084DAB9

$ apt-key list
pub   rsa2048 2010-10-19 [SCA] [expires: 2027-09-30]
      E298 A3A8 25C0 D65D FD57  CBB6 5171 6619 E084 DAB9
uid           [ unknown] Michael Rutter <marutter@gmail.com>
sub   rsa2048 2010-10-19 [E] [expires: 2027-09-30]
</pre>

An example for installing [https://cran.r-project.org/bin/linux/ubuntu/ R software] on Ubuntu
{{Pre}}
sudo apt update -qq
sudo apt install --no-install-recommends software-properties-common dirmngr

wget -qO- https://cloud.r-project.org/bin/linux/ubuntu/marutter_pubkey.asc | sudo tee -a /etc/apt/trusted.gpg.d/cran_ubuntu_key.asc
# -qO- will print to standard output screen
# If we use "-q", it will save to the disk

gpg --show-keys /etc/apt/trusted.gpg.d/cran_ubuntu_key.asc 
# pub   rsa2048 2010-10-19 [SCA] [expires: 2027-09-30]
#       E298A3A825C0D65DFD57CBB651716619E084DAB9         <--- fingerprint
# uid                      Michael Rutter <marutter@gmail.com>
# sub   rsa2048 2010-10-19 [E] [expires: 2027-09-30]

sudo add-apt-repository "deb https://cloud.r-project.org/bin/linux/ubuntu $(lsb_release -cs)-cran40/"
</pre>
More info: 
* [https://itsfoss.com/key-is-stored-in-legacy-trusted-gpg/ Fixing "Key is stored in legacy trusted.gpg keyring" Issue in Ubuntu]
* [https://manpages.ubuntu.com/manpages/xenial/man8/apt-key.8.html apt-key commands list/add/del]
** '''apt-key list''': This command lists the trusted keys that are currently stored in the /etc/apt/trusted.gpg file and the /etc/apt/trusted.gpg.d directory
** '''apt-key add''' [filename]
** '''apt-key del''' [keyid]

== Setup APT Proxy ==
[https://www.howtoforge.com/how-to-setup-apt-proxy-on-ubuntu/ How to Setup APT Proxy on Ubuntu 20.04 LTS]

= E: Could not get lock /var/lib/dpkg/lock =
I get the above message when I run '''sudo apt-get update''' on a virtual machine that I have not used for a long time (on Ubuntu click 'Show Applications' and type '''Logs'''). Many people also reported this problem. The following shows the reason why I got the error. My case seems to be related to the process ''apt.systemd.daily''. Read the comment by  Kjetil S from the link in Solution 1 below. One easy solution I did is to reboot the machine. 
<pre>
brb@ubuntu1804:~/Downloads$ sudo apt install mupdf
E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?
brb@ubuntu1804:~/Downloads$ ps aux | grep -i apt
root      1327  0.0  0.0   4628   772 ?        Ss   09:26   0:00 /bin/sh /usr/lib/apt/apt.systemd.daily update
root      1371  0.0  0.0   4628  1780 ?        S    09:26   0:00 /bin/sh /usr/lib/apt/apt.systemd.daily lock_is_held update
_apt      3902  3.0  0.2  88932  8636 ?        S    09:29   0:05 /usr/lib/apt/methods/http
brb       4516  0.0  0.0  21536  1032 pts/0    S+   09:32   0:00 grep --color=auto -i apt
</pre>

'''Solution 1:'''

[http://askubuntu.com/questions/15433/unable-to-lock-the-administration-directory-var-lib-dpkg-is-another-process Unable to lock the administration directory (/var/lib/dpkg/) is another process using it?]. 

I can reproduce the error from a clean boot. The most possible explanation is the answer from poolie: 

''the command-line apt overlaps with update-manager automatically polling. So if you try again in a few minutes that should fix it.'' 

From my experience, after I wait about 10 minutes, '''ps -A | grep apt''' won't show anything.

'''Solution 2:'''

[http://www.tecmint.com/fix-unable-to-lock-the-administration-directory-var-lib-dpkg-lock/ Fix “Unable to lock the administration directory (/var/lib/dpkg/)” in Ubuntu]
<syntaxhighlight lang='bash'>
# Method 1: Find and Kill all apt-get or apt Processes
$ ps -A | grep apt
1760 ?    00:00:00 apt.systemd.dai
3489 ?    00:00:00 aptd
$ sudo kill -9 1760
$ sudo kill -9 3489
$ sudo apt-get install keepass2
E: dpkg was interrupted, you must manually run 'sudo dpkg --configure -a' to correct the problem.

# Method 2: Delete the lock Files
sudo rm /var/lib/apt/lists/lock
# and 
sudo rm /var/lib/dpkg/lock
</syntaxhighlight>

= How To Force APT Package Manager To Use IPv4 In Ubuntu 16.04 =
https://www.ostechnix.com/how-to-force-apt-package-manager-to-use-ipv4-in-ubuntu-16-04/

= dpkg error: Package is in a very bad inconsistent state =
https://askubuntu.com/questions/148715/how-to-fix-package-is-in-a-very-bad-inconsistent-state-error

The following solution works for me (''zramswap-enabler'' in this example).
<syntaxhighlight lang='bash'>
# Remove the broken package via the following command:
sudo dpkg --remove --force-remove-reinstreq zramswap-enabler

# Install the package again:
sudo apt-get install zramswap-enabler
</syntaxhighlight>

= Difference between dpkg and aptitude/apt-get/gdebi =
* https://askubuntu.com/questions/309113/what-is-the-difference-between-dpkg-and-aptitude-apt-get
* [https://www.makeuseof.com/apt-vs-dpkg/ What’s the Difference Between APT and dpkg in Ubuntu?] When APT (or its cousin, Apt-get) installs a package, it's actually using '''dpkg''' on the back-end to accomplish that. In that way, '''dpkg''' acts more as an "under the hood" tool for APT's more user-friendly interface.

== apt vs. apt-get ==
[https://www.howtogeek.com/791055/apt-vs.-apt-get-whats-the-difference-on-linux/ apt vs. apt-get: What’s the Difference on Linux?]

= Some useful apt commands =
* [https://www.cyberciti.biz/faq/ubuntu-lts-debian-linux-apt-command-examples/ 19 Ubuntu / Debian Linux apt Command Examples]
* [https://opensource.com/article/21/6/apt-linux Linux package management with apt]
** Finding software: '''apt search cockpit'''
** Package metadata: '''apt show cockpit'''
** What package provides a file?: '''apt-file search qmake-qt5'''
** What files are included in a package?: '''apt-file list cockpit'''
** Removing an application: '''sudo apt purge apt-file''' & '''sudo apt autoremove'''

= deb file =
== Show deb file information ==
<pre>
dpkg-deb -I XXX.deb

dpkg-deb -c XXX.deb # list file content
</pre>

== Install a deb file (including dependencies): dpkg command ==
The dpkg -i command is lower level and has the following advantages: Direct control (you want to handle dependencies manually) and offline installation. On the other hand, the apt install command is higher level and has these advantages: Dependence resolution and repository access.
<syntaxhighlight lang='bash'>
sudo apt install ./application.deb
# OR
# dpkg gives more clear about the error message
sudo dpkg -i application.deb
</syntaxhighlight>
Note:

1. Remember to add "./" before the package name when we use the "apt install" command because "apt install" expect a package name or a full path to a deb file ("application.deb" is neither a package name or a full path).

2. However, installing from a .deb file through dpkg does not resolve dependency issues the same way installation through apt will. See [https://askubuntu.com/questions/784935/unable-to-install-r-studio here] and [https://linuxhint.com/install-dpkg-dependencies-automatically/ How to let dpkg Install Dependencies Automatically]. So you should run '''sudo apt-get install -f''' to fix and install dependencies. After that, run the '''sudo dpkg -i application.deb''' again. 

<syntaxhighlight lang='bash'>
sudo apt install -f dep1.deb dep2.deb # NOT apt -f install XXX.deb
</syntaxhighlight>

3. The advantage of using apt over dpkg is that apt will automatically resolve and install any dependencies required by the .deb package, whereas with dpkg you would have to manually resolve them using sudo apt-get install -f.

4. Another way to install a deb file is using the '''gdebi''' tool.

== How to install .deb package with double click ==
Right click a deb file and choose "Software Install". 

But if it is an upgrade of an existing software, it can only let you remove it and can't upgrade.

== Remove deb packages ==
See the [http://manpages.ubuntu.com/manpages/trusty/man1/dpkg.1.html man page].
<syntaxhighlight lang='bash'>
dpkg -l | grep 'tcl'
sudo dpkg -r tcl8.4 # -r means remove/uninstall
sudo dpkg -P tcl8.4 # -P means purge

dpkg -l | grep 'tcl'   (optional)
</syntaxhighlight>

= gdebi: an improvement over dpkg =
[https://askubuntu.com/questions/621351/gdebi-vs-dpkg-how-does-gdebi-automatically-gets-missing-dependancies-can-i-u How does gdebi automatically gets missing dependancies ? Can I use gdebi for all other installations of .deb packages?]

<syntaxhighlight lang='bash'>
sudo apt-get install gdebi-core

# wget newPackage.deb
# sudo gdebi -n newPackage.deb
</syntaxhighlight>

= deb files caches =
See http://askubuntu.com/questions/444240/ubuntu-updates-blocked-apt-get
<pre>
sudo rm -f /etc/apt/sources.list.d/*    # PPA list

sudo dpkg -i /var/cache/apt/archives/*.deb

sudo dpkg --configure -a
</pre>

= apt-cache =
[http://itsfoss.com/apt-cache-command How to Use apt-cache Command in Debian, Ubuntu and Other Linux Distributions]

== /var/lib/apt/lists ==
https://unix.stackexchange.com/questions/217369/clear-apt-get-list

== List all available packages (from repositories) ==
<syntaxhighlight lang='bash'>
apt-cache pkgnames # pkgnames is part of the command
</syntaxhighlight>

Examples:
<pre>
$ apt list | wc -l
WARNING: apt does not have a stable CLI interface. Use with caution in scripts.
76113

$ apt list --installed  | wc -l
WARNING: apt does not have a stable CLI interface. Use with caution in scripts.
2816

$ apt-cache pkgnames | wc -l
71223
</pre>

== Show package information and list all versions ==
Note the <package> does not have to be installed.
<syntaxhighlight lang='bash'>
apt-cache show <package_name>
apt-cache show <package_name> | grep Version
</syntaxhighlight>
What is the difference of '''apt show ''' and '''apt-cache show'''?

== How can I see all versions of a package that are available ==
We can use the '''show''' or [https://askubuntu.com/a/2108 madison] parameter in '''apt-cache'''. For example,
<syntaxhighlight lang='bash'>
apt-cache show <package_name> | grep Version
apt-cache madison <package_name> # wide output, include repository URLs
</syntaxhighlight>

== Show the candidcate version and whether any version is installed ==
<syntaxhighlight lang='bash'>
apt-cache policy <package_name>
</syntaxhighlight>
For example, I don't have apache2 installed.
<pre>
$ apt-cache policy apache2
apache2:
  Installed: (none)
  Candidate: 2.4.41-4ubuntu3.11
  Version table:
     2.4.41-4ubuntu3.11 500
        500 http://us.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
     2.4.41-4ubuntu3.10 500
        500 http://security.ubuntu.com/ubuntu focal-security/main amd64 Packages
     2.4.41-4ubuntu3 500
        500 http://us.archive.ubuntu.com/ubuntu focal/main amd64 Packages
</pre>

== Check dependencies for specific packages ==
[https://www.makeuseof.com/how-to-check-package-dependencies-in-ubuntu/ How to List Dependencies of a Package in Ubuntu]

<syntaxhighlight lang='bash'>
$ apt depends r-base # or apt-cache depends r-base
r-base
  Depends: r-base-core (>= 3.6.3-1bionic)
  Depends: r-recommended (= 3.6.3-1bionic)
  Recommends: r-base-html
  Recommends: r-doc-html
  Suggests: elpa-ess
 |Suggests: r-doc-info
  Suggests: r-doc-pdf

$ apt-cache showpkg <package_name>
</syntaxhighlight>

== Checking dependencies and reverse dependencies with apt-rdepends ==
[https://itsfoss.com/check-dependencies-package-ubuntu/ How to Check Dependencies of a Package in Ubuntu/Debian-based Linux Distributions]

<syntaxhighlight lang='bash'>
$ sudo apt install apt-rdepends
$ apt-rdepends -r inxi
Reading package lists... Done
Building dependency tree       
Reading state information... Done
inxi
  Reverse Depends: forensics-extra (2.14)
forensics-extra
  Reverse Depends: forensics-full (2.14)
forensics-full

$ apt-rdepends -r sysbench
Reading package lists... Done
Building dependency tree       
Reading state information... Done
sysbench
  Reverse Depends: hardinfo (0.6~alpha~git20211203~focal)
hardinfo
$ apt-cache depends  hardinfo
hardinfo
  Depends: pciutils
    pciutils:i386
  Depends: zlib1g-dev
  Depends: dmidecode
    dmidecode:i386
  Depends: fwupd
  Depends: lm-sensors
  Depends: sysbench
  Depends: usbutils
    usbutils:i386
  Depends: libc6
  Depends: libcairo2
  Depends: libgdk-pixbuf2.0-0
  Depends: libglib2.0-0
  Depends: libgtk-3-0
  Depends: libjson-glib-1.0-0
  Depends: libpango-1.0-0
  Depends: libpangocairo-1.0-0
  Depends: libsoup2.4-1
  Depends: libx11-6
  Suggests: mesa-utils
</syntaxhighlight>

= List racing games package (kind of search packages by key words) =
<syntaxhighlight lang='bash'>
apt-cache search racing game
apt-cache search vsftpd
</syntaxhighlight>

= depends, recommends and suggests =
[https://askubuntu.com/questions/117635/how-to-install-suggested-packages-in-apt-get How to install suggested packages in apt-get]

By default, ''apt-get'' installs recommended packages.

Your option '''--install-suggests''' adds in the suggested packages and their suggested dependencies.

Note that --install-suggests will be recursive. It may install ''a lot'' of packages.

= Download debs and then upgrade =
<pre>
sudo apt-get upgrade --download-only
sudo apt-get upgrade
# sudo apt-get upgrade --no-download
</pre>

= Upgrade a package =
<syntaxhighlight lang='bash'>
apt-get install <package_name>

sudo apt --only-upgrade install package_name
# It won’t install the given package if it is not already installed
</syntaxhighlight>

= Install specific version of the package =
Use the "=" with the package-name and append desired version.
<syntaxhighlight lang='bash'>
sudo apt-get install vsftpd=2.3.5-3ubuntu1
</syntaxhighlight>

= Remove a package =
[https://www.cyberciti.biz/faq/linux-uninstall-package-software-using-the-cli/ Linux uninstall package / software using the CLI] 

<syntaxhighlight lang='bash'>
sudo apt-get remove <package_name>
</syntaxhighlight>

To completely remove a package including their configuration files
<syntaxhighlight lang='bash'>
sudo apt-get purge <package_name>
sudo apt-get remove --purge <package_name>

# examples
sudo apt remove --purge libreoffice
sudo apt remove --purge thunderbird
</syntaxhighlight>

[https://www.linuxfordevices.com/tutorials/ubuntu/uninstalling-packages-with-apt#Whats-the-difference-between-remove-and-purge What’s the difference between ‘remove‘ and ‘purge‘ ?] The primary difference being ‘remove‘ and ‘purge‘ is that ‘remove‘ only gets rid of the package leaving any configuration files untouched. Whereas ‘purge‘ not only removes the package but also removes all configuration files OUTSIDE THE HOME DIRECTORY.

= Rollback an apt-get upgrade =
http://www.cyberciti.biz/howto/debian-linux/ubuntu-linux-rollback-an-apt-get-upgrade/

= Clean up disk space =
The clean command is used to free up the disk space by cleaning retrieved .deb files from the local repository.
<syntaxhighlight lang='bash'>
sudo apt-get clean
</syntaxhighlight>

= Auto clean up apt-get cache =
<pre>
sudo apt-get autoclean
</pre>
The 'autoclean' command deletes all .deb files from '''/var/cache/apt/archives''' to free up disk space.

[https://askubuntu.com/a/3169 What is difference between the options "autoclean", "autoremove" and "clean"?] From the apt-get man page: '''autoclean''': Like clean, autoclean clears out the local repository of retrieved package files. The difference is that it only removes package files that can no longer be downloaded, and are largely useless. This allows a cache to be maintained over a long period without it growing out of control. The configuration option APT::Clean-Installed will prevent installed packages from being erased if it is set to off.

= Download only source code of package =
<pre>
sudo apt-get --download-only source <package_name>
</pre>

To download and unpack source code of a package
<pre>
sudo apt-get source <package_name>
</pre>

To download, unpack and compile a package
<pre>
sudo apt-get --compile source <package_name>
</pre>

= Download without installing =
<pre>
sudo apt-get download <package_name>
</pre>

= Check change log of package =
Note that the change log may not be found.
<pre>
sudo apt-get changelog <package_name>
</pre>

= Simulate installing packages =
<syntaxhighlight lang='bash'>
$ sudo apt-get -s install packagename

$ sudo apt-get -s build-dep packagename
$ man apt-get
</syntaxhighlight>

'''Generally, it is good to build-dep then install package.'''

= Check broken dependencies =
<syntaxhighlight lang='bash'>
sudo apt-get check
</syntaxhighlight>

= Fix broken packages =
[https://www.makeuseof.com/how-to-find-and-fix-broken-packages-on-linux/ How to Find and Fix Broken Packages on Linux]
<pre>
sudo apt --fix-missing update
sudo apt update
sudo apt install -f
</pre>

== Not all updates can be installed: partial upgrade ==
[https://itectec.com/ubuntu/ubuntu-not-all-updates-can-be-installed-partial-upgrade/ Not all updates can be installed: partial upgrade], [https://askubuntu.com/questions/1334791/not-all-updates-can-be-installed-in-software-updater Not all updates can be installed in software updater]
<pre>
$ sudo update-manager
$ sudo apt-get install -f
</pre>

= Search a package =
* [https://itsfoss.com/install-zlib-ubuntu/ How to Install Zlib on Ubuntu Linux]. Use the '''apt search''' command
* [https://itsfoss.com/apt-search-command/ Using ‘apt search’ and ‘apt show’ Commands to Search and Find Details of Packages in Ubuntu]

= Search missing package's full name =
Use the '''apt-file''' command. See [http://kobablog.wordpress.com/2011/05/17/how-to-find-and-install-the-missing-file-in-ubuntu/ this post]

At first, install apt-file command and prepare it.
<syntaxhighlight lang='bash'>
$ sudo apt-get install apt-file
$ sudo apt-file update
</syntaxhighlight>

To find zlib.h,
<syntaxhighlight lang='bash'>
$ apt-file search zlib.h
</syntaxhighlight>

It reports too many result. Let’s narrow down.
<syntaxhighlight lang='bash'>
$ apt-file search /usr/include/zlib.h
zlib1g-dev: /usr/include/zlib.h
</syntaxhighlight>

Now you know zlib.h is in zlib1g-dev package.
<syntaxhighlight lang='bash'>
$ sudo apt-get install zlib1g-dev
</syntaxhighlight>

= Find package information before installing it =
Use "-s" option for simulation. No sudo is necessary.
<pre>
apt-get -s install PACKAGENAME
</pre>
The output is too much (include other dependences)

A better way is to use '''aptitude''' (which is not installed by default in Ubuntu)
<pre>
aptitude search <package> -F "%c %p %d %V"
</pre>
For example,
<pre>
debian@beaglebone:~/qt-4.8.5/bin$ aptitude search  qtcreator -F "%c %p %d %V"
p qtcreator                         lightweight integrated development environme 2.5.0-2       
p qtcreator:armel                   lightweight integrated development environme 2.5.0-2       
p qtcreator-dbg                     debugging symbols for Qt Creator IDE         2.5.0-2       
p qtcreator-dbg:armel               debugging symbols for Qt Creator IDE         2.5.0-2       
p qtcreator-doc                     documentation for Qt Creator IDE             2.5.0-2   
</pre>

If a package is already installed, we can use the following way to check version number.
<pre>
apt-show-versions <package>
</pre>

'''dpkg''' Command : View Package Information On Debian/Ubuntu/Mint Systems
<syntaxhighlight lang='bash'>
dpkg -s r-base
</syntaxhighlight>

'''aptitude''' Command : View Package Information On Debian/Ubuntu/Mint Systems
<syntaxhighlight lang='bash'>
aptitude show htop
</syntaxhighlight>

= List files in a package =
<pre>
dpkg -L <package_name>
</pre>

= Search installed packages =
<syntaxhighlight lang='bash'>
dpkg -l libgtk* | grep -e '^i'
dpkg -l libpng* | grep -e '^i'
dpkg -l libjpeg* | grep -e '^i'
</syntaxhighlight>

To search x-org related packages
<syntaxhighlight lang='bash'>
udooer@udoo:~$ dpkg -l | grep xserver-xorg | awk '{$1=$3=$4=""; print $0}'  # Skip columns 1,3,4
 imx-xserver-xorg-extension-viv-9t6-hdmi   Freescale Xorg server driver extension for HDMI performance
 imx-xserver-xorg-video-viv-9t6   Xorg server driver for imx6, vivante
 xserver-xorg   X.Org X server
 xserver-xorg-core   Xorg X server - core server
 xserver-xorg-dev   Xorg X server - development files
 xserver-xorg-input-all   X.Org X server -- input driver metapackage
 xserver-xorg-input-evdev   X.Org X server -- evdev input driver
 xserver-xorg-input-synaptics   Synaptics TouchPad driver for X.Org server
 xserver-xorg-input-wacom   X.Org X server -- Wacom input driver
 xserver-xorg-video-all   X.Org X server -- output driver metapackage
 xserver-xorg-video-fbdev   X.Org X server -- fbdev display driver
 xserver-xorg-video-modesetting   X.Org X server -- Generic modesetting driver
 xserver-xorg-video-omap   X.Org X server -- OMAP display driver
 xserver-xorg-video-vesa   X.Org X server -- VESA display driver
</syntaxhighlight>

= List of installed packages =
<syntaxhighlight lang='bash'>
apt list --installed | wc -l
# Or using [https://wiki.debian.org/ListInstalledPackages dpkg-query] utility.
dpkg-query -l

dpkg --get-selections 
</syntaxhighlight>

= Show A History Of Installed, Upgraded Or Removed Packages =
https://www.linuxuprising.com/2019/01/how-to-show-history-of-installed.html?m=1

<syntaxhighlight lang='bash'>
# recently installed packages, their version number
grep "install " /var/log/dpkg.log

# recently upgraded packages, as well as the old and new package version
grep "upgrade " /var/log/dpkg.log

# recently removed packages
grep "remove " /var/log/dpkg.log
</syntaxhighlight>

'''/var/log/dpkg.log''' contains the package install, update and remove history for the current month. For the previous month, read the '''/var/log/dpkg.log.1''' log file. Want to go back even more in the dpkg history? Use zgrep instead of grep, and read /var/log/dpkg.log.2.gz, /var/log/dpkg.log.3.gz, /var/log/dpkg.log.4.gz and so on (up to 12 months),
<syntaxhighlight lang='bash'>
grep "install " /var/log/dpkg.log.1

zgrep "upgrade " /var/log/dpkg.log.2.gz
</syntaxhighlight>

= Install a list of packages =
[https://www.cyberciti.biz/faq/how-to-list-all-installed-packages-debian-ubuntu/ How to get list of installed packages on Ubuntu / Debian Linux]

Suppose we want to install all packages currently installed on server 1 onto server 2, we can do that by
<syntaxhighlight lang='bash'>
# server 1
dpkg --get-selections | grep -v deinstall > mylist.txt
# server 2
sudo dpkg --set-selections < mylist.txt
</syntaxhighlight>

= Show (sort) package size =
<pre>
dpkg-query -Wf '${Installed-Size}\t${Package}\n' | sort -n
</pre>

= Check if a library is installed or not ('''ldconfig''') =
Use '''ldconfig -p | grep LIBNAME''' ('-p' is used to print the list stored in the current cache). For example, to check if ''libxml'' is installed or not, then following code will output the number of matches if it was found.
<syntaxhighlight lang='bash'>
EXIST=`ldconfig -p | grep libxml | wc -l`
if [ $EXIST -ne 0 ]; then echo $EXIST; fi
</syntaxhighlight>

The following code will search "libQt" and the library version will be shown in the file name.
<syntaxhighlight lang='bash'>
ldconfig -p | grep libQt
# On Ubuntu 14.04, 16.04:
# libQtGui.so.4 (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/libQtGui.so.4
# On Ubuntu 17.10, 18.04:
# libQt5Gui.so.5 (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
</syntaxhighlight>

To install libQtGui.so.4 in Ubuntu 18.04, run the command
<syntaxhighlight lang='bash'>
sudo apt-get install libqtgui4
</syntaxhighlight>

See also the '''[[C#Show_all_libraries_used_.28dynamically_linked.29_by_an_executable_program|ldd]]''' command to print all dynamic dependencies of an executable program.

= How to uninstall software =
http://www.howtogeek.com/229699/how-to-uninstall-software-using-the-command-line-in-linux/

= Upgrade software packages =
Upgrade all the currently installed software packages on the system
<syntaxhighlight lang='bash'>
sudo apt-get upgrade
</syntaxhighlight>

If you want to upgrade, unconcerned of whether software packages will be added or removed to fulfill dependencies, use 
<syntaxhighlight lang='bash'>
sudo apt-get dist-upgrade
</syntaxhighlight>

= List of available (uninstalled) packages =
<syntaxhighlight lang='bash'>
aptitude -F "%p" search "?not(?installed)"
</syntaxhighlight>
See http://superuser.com/questions/408082/how-do-i-get-a-list-of-available-i-e-uninstalled-packages-in-debian

= Check Change Log of Package =
<syntaxhighlight lang='bash'>
sudo apt-get changelog PKGNAME
</syntaxhighlight>

= Clean up/remove packages =
[http://www.ubuntugeek.com/cleaning-up-a-ubuntu-gnulinux-system-updated-with-ubuntu-14-10-and-more-tools-added.html ubuntugeek.com]

= PPA =
[https://linuxhint.com/ppa_repositories_ubuntu/ A Guide to Using PPA Repositiories in Ubuntu]

== unmet dependencies when trying to install okular ==
This happened on Ubuntu 20.04
<pre>
The following packages have unmet dependencies:
 okular : Depends: libokular5core9 (= 4:19.12.3-2ubuntu1) but it is not going to be installed
          Depends: phonon4qt5 but it is not going to be installed
          Recommends: okular-extra-backends but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
</pre>
'''GNOME software''' can install Okular without any issue.

== unmet dependencies after adding a PPA & apt --fix-broken ==
http://askubuntu.com/questions/140246/how-do-i-resolve-unmet-dependencies-after-adding-a-ppa

<syntaxhighlight lang='bash'>
$ sudo apt-get install libgl1-mesa.dev
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Note, selecting 'libgl1-mesa-dev-lts-quantal' for regex 'libgl1-mesa.dev'
Note, selecting 'libgl1-mesa-dev' for regex 'libgl1-mesa.dev'
Note, selecting 'libgl1-mesa-dev-lts-saucy' for regex 'libgl1-mesa.dev'
Note, selecting 'libgl1-mesa-dev-lts-trusty' for regex 'libgl1-mesa.dev'
Note, selecting 'libgl1-mesa-dev-lts-utopic' for regex 'libgl1-mesa.dev'
Note, selecting 'libgl1-mesa-dev-lts-vivid' for regex 'libgl1-mesa.dev'
Note, selecting 'libgl1-mesa-dev-lts-raring' for regex 'libgl1-mesa.dev'
libgl1-mesa-dev is already the newest version.
libgl1-mesa-dev set to manually installed.
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 libgl1-mesa-dev : Conflicts: libgl-dev
                   Conflicts: libgl1-mesa-dri-dev
 libgl1-mesa-dev-lts-utopic : Depends: mesa-common-dev-lts-utopic (= 10.3.2-0ubuntu1~trusty2) but it is not going to be installed
                              Depends: libgl1-mesa-glx-lts-utopic (= 10.3.2-0ubuntu1~trusty2) but it is not going to be installed
                              Conflicts: libgl-dev
                              Conflicts: libgl1-mesa-dev
                              Conflicts: libgl1-mesa-dri-dev
 libgl1-mesa-dev-lts-vivid : Depends: mesa-common-dev-lts-vivid (= 10.5.9-2ubuntu1~trusty2) but it is not going to be installed
                             Depends: libgl1-mesa-glx-lts-vivid (= 10.5.9-2ubuntu1~trusty2) but it is not going to be installed
                             Conflicts: libgl-dev
                             Conflicts: libgl1-mesa-dev
                             Conflicts: libgl1-mesa-dri-dev
                             Conflicts: xorg-renamed-package-lts-utopic
E: Unable to correct problems, you have held broken packages.
</syntaxhighlight>

[https://askubuntu.com/questions/914428/unmet-dependencies-when-trying-to-install-r-base/914429 Unmet dependencies when trying to install r-base] (Works on Ubuntu 16.04).
<syntaxhighlight lang='bash'>
sudo apt --fix-broken install
sudo apt-get update
sudo apt-get upgrade
</syntaxhighlight>

Another case: I installed R 4.0.0 using ''sudo add-apt-repository --yes ”ppa:edd/r-4.0” '' by following [http://dirk.eddelbuettel.com/papers/r4_upgrade_to_r400.pdf#page=9 this], then I remove and install the [https://cran.rstudio.com/bin/linux/ubuntu/README.html official one]. The above 3 commands does not help. (Ubuntu 18.04).
<pre>
The following packages have unmet dependencies:
 r-base : Depends: r-recommended (= 4.0.0-1.1804.0) but 4.0.0-1.1804.1 is to be installed
E: Unable to correct problems, you have held broken packages.
</pre>
The solution is to use '''Aptitude''' command. See [https://appuals.com/fix-unmet-dependencies-error-ubuntu/ How to Fix Unmet Dependencies Error on Ubuntu]
<pre>
$ sudo aptitude install r-base                                   9:55:45
The following NEW packages will be installed:
  r-base{b} 
0 packages upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 43.3 kB of archives. After unpacking 62.5 kB will be used.
The following packages have unmet dependencies:
 r-base : Depends: r-recommended (= 4.0.0-1.1804.0) but 4.0.0-1.1804.1 is installed
The following actions will resolve these dependencies:

     Keep the following packages at their current version:
1)     r-base [Not Installed]                             



Accept this solution? [Y/n/q/?] n
The following actions will resolve these dependencies:

     Downgrade the following packages:                                       
1)     r-recommended [4.0.0-1.1804.1 (now) -> 4.0.0-1.1804.0 (bionic-cran40)]



Accept this solution? [Y/n/q/?] 
The following packages will be DOWNGRADED:
  r-recommended 
The following NEW packages will be installed:
  r-base 
0 packages upgraded, 1 newly installed, 1 downgraded, 0 to remove and 0 not upgraded.
</pre>

= Fix broken Ubuntu =
[https://www.ostechnix.com/how-to-fix-broken-ubuntu-os-without-reinstalling-it/ How To Fix Broken Ubuntu OS Without Reinstalling It]
<syntaxhighlight lang='bash'>
$ sudo rm /var/lib/apt/lists/lock
$ sudo rm /var/lib/dpkg/lock
$ sudo rm /var/lib/dpkg/lock-frontend
$ sudo dpkg --configure -a
$ sudo apt clean
$ sudo apt update --fix-missing
$ sudo apt install -f
$ sudo dpkg --configure -a
$ sudo apt upgrade
$ sudo apt dist-upgrade
$ sudo reboot
</syntaxhighlight>

= Convert packages =
[https://www.makeuseof.com/how-to-convert-between-linux-packages-using-alien/ How to Convert Between Linux Packages Using Alien]