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RPM packages explained

<div style="margin: 5px 5% 10px 5%;"><img src="http://www.sickgaming.net/blog/wp-content/uploads/2019/06/rpm-packages-explained.png" width="1024" height="558" title="" alt="" /></div><div>Perhaps the best known way the Fedora community pursues its <a href="https://docs.fedoraproject.org/en-US/project/#_what_is_fedora_all_about">mission of promoting free and open source software and content</a> is by developing the <a href="https://getfedora.org">Fedora software distribution</a>. So it’s not a surprise at all that a very large proportion of our community resources are spent on this task. This post summarizes how this software is “packaged” and the underlying tools such as rpm that make it all possible.
 
<h2>RPM: the smallest unit of software</h2>
The editions and flavors (<a href="https://spins.fedoraproject.org/">spins</a>/<a href="https://labs.fedoraproject.org/">labs</a>/<a href="https://silverblue.fedoraproject.org/">silverblue</a>) that users get to choose from are all very similar. They’re all composed of various software that is mixed and matched to work well together. What differs between them is the exact list of tools that goes into each. That choice depends on the use case that they target. The basic unit of all of these is an RPM package file.
RPM files are archives that are similar to ZIP files or tarballs. In fact, they uses compression to reduce the size of the archive. However, along with files, RPM archives also contain metadata about the package. This can be queried using the rpm tool:
<pre class="wp-block-code"> <div class="codecolorer-container text default" style="overflow:auto;border:1px solid #9F9F9F;width:435px;height:300px"><div class="text codecolorer" style="padding:5px;font:normal 12px/1.4em Monaco, Lucida Console, monospace">$ rpm -q fpaste 
fpaste-0.3.9.2-2.fc30.noarch 
 
$ rpm -qi fpaste 
Name        : fpaste 
Version     : 0.3.9.2 
Release     : 2.fc30 
Architecture: noarch 
Install Date: Tue 26 Mar 2019 08:49:10 GMT 
Group       : Unspecified 
Size        : 64144 
License     : GPLv3+ 
Signature   : RSA/SHA256, Thu 07 Feb 2019 15:46:11 GMT, Key ID ef3c111fcfc659b9 
Source RPM  : fpaste-0.3.9.2-2.fc30.src.rpm 
Build Date  : Thu 31 Jan 2019 20:06:01 GMT 
Build Host  : buildhw-07.phx2.fedoraproject.org 
Relocations : (not relocatable) 
Packager    : Fedora Project 
Vendor      : Fedora Project 
URL         : https://pagure.io/fpaste 
Bug URL     : https://bugz.fedoraproject.org/fpaste 
Summary     : A simple tool for pasting info onto sticky notes instances 
Description : 
It is often useful to be able to easily paste text to the Fedora 
Pastebin at http://paste.fedoraproject.org and this simple script 
will do that and return the resulting URL so that people may 
examine the output. This can hopefully help folks who are for 
some reason stuck without X, working remotely, or any other 
reason they may be unable to paste something into the pastebin 
 
$ rpm -ql fpaste 
/usr/bin/fpaste 
/usr/share/doc/fpaste 
/usr/share/doc/fpaste/README.rst 
/usr/share/doc/fpaste/TODO 
/usr/share/licenses/fpaste 
/usr/share/licenses/fpaste/COPYING 
/usr/share/man/man1/fpaste.1.gz</div></div> </pre>
When an RPM package is installed, the rpm tools know exactly what files were added to the system. So, removing a package also removes these files, and leaves the system in a consistent state. This is why installing software using rpm is preferred over installing software from source whenever possible. 
<h2>Dependencies</h2>
Nowadays, it is quite rare for software to be completely self-contained. Even <a href="https://src.fedoraproject.org/rpms/fpaste">fpaste</a>, a simple one file Python script, requires that the Python interpreter be installed. So, if the system does not have Python installed (highly unlikely, but possible), fpaste cannot be used. In packager jargon, we say that “Python is a run-time dependency of fpaste“.
When RPM packages are built (the process of building RPMs is not discussed in this post), the generated archive includes all of this metadata. That way, the tools interacting with the RPM package archive know what else must must be installed so that fpaste works correctly:
<pre class="wp-block-code"> <div class="codecolorer-container text default" style="overflow:auto;border:1px solid #9F9F9F;width:435px;height:300px"><div class="text codecolorer" style="padding:5px;font:normal 12px/1.4em Monaco, Lucida Console, monospace">$ rpm -q --requires fpaste 
/usr/bin/python3 
python3 
rpmlib(CompressedFileNames) &lt;= 3.0.4-1 
rpmlib(FileDigests) &lt;= 4.6.0-1 
rpmlib(PayloadFilesHavePrefix) &lt;= 4.0-1 
rpmlib(PayloadIsXz) &lt;= 5.2-1 
 
$ rpm -q --provides fpaste 
fpaste = 0.3.9.2-2.fc30 
 
$ rpm -qi python3 
Name        : python3 
Version     : 3.7.3 
Release     : 3.fc30 
Architecture: x86_64 
Install Date: Thu 16 May 2019 18:51:41 BST 
Group       : Unspecified 
Size        : 46139 
License     : Python 
Signature   : RSA/SHA256, Sat 11 May 2019 17:02:44 BST, Key ID ef3c111fcfc659b9 
Source RPM  : python3-3.7.3-3.fc30.src.rpm 
Build Date  : Sat 11 May 2019 01:47:35 BST 
Build Host  : buildhw-05.phx2.fedoraproject.org 
Relocations : (not relocatable) 
Packager    : Fedora Project 
Vendor      : Fedora Project 
URL         : https://www.python.org/ 
Bug URL     : https://bugz.fedoraproject.org/python3 
Summary     : Interpreter of the Python programming language 
Description : 
Python is an accessible, high-level, dynamically typed, interpreted programming 
language, designed with an emphasis on code readability. 
It includes an extensive standard library, and has a vast ecosystem of 
third-party libraries. 
 
The python3 package provides the "python3" executable: the reference 
interpreter for the Python language, version 3. 
The majority of its standard library is provided in the python3-libs package, 
which should be installed automatically along with python3. 
The remaining parts of the Python standard library are broken out into the 
python3-tkinter and python3-test packages, which may need to be installed 
separately. 
 
Documentation for Python is provided in the python3-docs package. 
 
Packages containing additional libraries for Python are generally named with 
the "python3-" prefix. 
 
$ rpm -q --provides python3 
python(abi) = 3.7 
python3 = 3.7.3-3.fc30 
python3(x86-64) = 3.7.3-3.fc30 
python3.7 = 3.7.3-3.fc30 
python37 = 3.7.3-3.fc30</div></div> </pre>
<h2>Resolving RPM dependencies</h2>
While rpm knows the required dependencies for each archive, it does not know where to find them. This is by design: rpm only works on local files and must be told exactly where they are. So, if you try to install a single RPM package, you get an error if rpm cannot find the package’s run-time dependencies. This example tries to install a package downloaded from the Fedora package set:
<pre class="wp-block-code"> <div class="codecolorer-container text default" style="overflow:auto;border:1px solid #9F9F9F;width:435px;height:300px"><div class="text codecolorer" style="padding:5px;font:normal 12px/1.4em Monaco, Lucida Console, monospace">$ ls 
python3-elephant-0.6.2-3.fc30.noarch.rpm 
 
$ rpm -qpi python3-elephant-0.6.2-3.fc30.noarch.rpm 
Name        : python3-elephant 
Version     : 0.6.2 
Release     : 3.fc30 
Architecture: noarch 
Install Date: (not installed) 
Group       : Unspecified 
Size        : 2574456 
License     : BSD 
Signature   : (none) 
Source RPM  : python-elephant-0.6.2-3.fc30.src.rpm 
Build Date  : Fri 14 Jun 2019 17:23:48 BST 
Build Host  : buildhw-02.phx2.fedoraproject.org 
Relocations : (not relocatable) 
Packager    : Fedora Project 
Vendor      : Fedora Project 
URL         : http://neuralensemble.org/elephant 
Bug URL     : https://bugz.fedoraproject.org/python-elephant 
Summary     : Elephant is a package for analysis of electrophysiology data in Python 
Description : 
Elephant - Electrophysiology Analysis Toolkit Elephant is a package for the 
analysis of neurophysiology data, based on Neo. 
 
$ rpm -qp --requires python3-elephant-0.6.2-3.fc30.noarch.rpm 
python(abi) = 3.7 
python3.7dist(neo) >= 0.7.1 
python3.7dist(numpy) >= 1.8.2 
python3.7dist(quantities) >= 0.10.1 
python3.7dist(scipy) >= 0.14.0 
python3.7dist(six) >= 1.10.0 
rpmlib(CompressedFileNames) &lt;= 3.0.4-1 
rpmlib(FileDigests) &lt;= 4.6.0-1 
rpmlib(PartialHardlinkSets) &lt;= 4.0.4-1 
rpmlib(PayloadFilesHavePrefix) &lt;= 4.0-1 
rpmlib(PayloadIsXz) &lt;= 5.2-1 
 
$ sudo rpm -i ./python3-elephant-0.6.2-3.fc30.noarch.rpm 
error: Failed dependencies: 
        python3.7dist(neo) >= 0.7.1 is needed by python3-elephant-0.6.2-3.fc30.noarch 
        python3.7dist(quantities) >= 0.10.1 is needed by python3-elephant-0.6.2-3.fc30.noarch</div></div> </pre>
In theory, one could download all the packages that are required for python3-elephant, and tell rpm where they all are, but that isn’t convenient. What if python3-neo and python3-quantities have other run-time requirements and so on? Very quickly, the dependency chain can get quite complicated.
<h3>Repositories</h3>
Luckily, dnf and friends exist to help with this issue. Unlike rpm, dnf is aware of repositories. Repositories are collections of packages, with metadata that tells dnf what these repositories contain. All Fedora systems come with the default Fedora repositories enabled by default:
<pre class="wp-block-code"> <div class="codecolorer-container text default" style="overflow:auto;border:1px solid #9F9F9F;width:435px"><div class="text codecolorer" style="padding:5px;font:normal 12px/1.4em Monaco, Lucida Console, monospace">$ sudo dnf repolist 
repo id              repo name                             status 
fedora               Fedora 30 - x86_64                    56,582 
fedora-modular       Fedora Modular 30 - x86_64               135 
updates              Fedora 30 - x86_64 - Updates           8,573 
updates-modular      Fedora Modular 30 - x86_64 - Updates     138 
updates-testing      Fedora 30 - x86_64 - Test Updates      8,458</div></div> </pre>
There’s more information on <a href="https://docs.fedoraproject.org/en-US/quick-docs/repositories/">these repositories</a>, and how they <a href="https://docs.fedoraproject.org/en-US/quick-docs/adding-or-removing-software-repositories-in-fedora/">can be managed</a> on the Fedora quick docs. 
dnf can be used to query repositories for information on the packages they contain. It can also search them for software, or install/uninstall/upgrade packages from them:
<pre class="wp-block-code"> <div class="codecolorer-container text default" style="overflow:auto;border:1px solid #9F9F9F;width:435px"><div class="text codecolorer" style="padding:5px;font:normal 12px/1.4em Monaco, Lucida Console, monospace">$ sudo dnf search elephant 
Last metadata expiration check: 0:05:21 ago on Sun 23 Jun 2019 14:33:38 BST. 
============================================================================== Name &amp; Summary Matched: elephant ============================================================================== 
python3-elephant.noarch : Elephant is a package for analysis of electrophysiology data in Python 
python3-elephant.noarch : Elephant is a package for analysis of electrophysiology data in Python 
 
$ sudo dnf list \*elephant\* 
Last metadata expiration check: 0:05:26 ago on Sun 23 Jun 2019 14:33:38 BST. 
Available Packages 
python3-elephant.noarch      0.6.2-3.fc30      updates-testing 
python3-elephant.noarch      0.6.2-3.fc30              updates</div></div> </pre>
<h3>Installing dependencies</h3>
When installing the package using dnf now, it resolves all the required dependencies, then calls rpm to carry out the transaction:
<pre class="wp-block-code"> <div class="codecolorer-container text default" style="overflow:auto;border:1px solid #9F9F9F;width:435px;height:300px"><div class="text codecolorer" style="padding:5px;font:normal 12px/1.4em Monaco, Lucida Console, monospace">$ sudo dnf install python3-elephant 
Last metadata expiration check: 0:06:17 ago on Sun 23 Jun 2019 14:33:38 BST. 
Dependencies resolved. 
============================================================================================================================================================================================== 
 Package                                      Architecture                     Version                                                        Repository                                 Size 
============================================================================================================================================================================================== 
Installing: 
 python3-elephant                             noarch                           0.6.2-3.fc30                                                   updates-testing                           456 k 
Installing dependencies: 
 python3-neo                                  noarch                           0.8.0-0.1.20190215git49b6041.fc30                              fedora                                    753 k 
 python3-quantities                           noarch                           0.12.2-4.fc30                                                  fedora                                    163 k 
Installing weak dependencies: 
 python3-igor                                 noarch                           0.3-5.20150408git2c2a79d.fc30                                  fedora                                     63 k 
 
Transaction Summary 
============================================================================================================================================================================================== 
Install  4 Packages 
 
Total download size: 1.4 M 
Installed size: 7.0 M 
Is this ok [y/N]: y 
Downloading Packages: 
(1/4): python3-igor-0.3-5.20150408git2c2a79d.fc30.noarch.rpm                                                                                                  222 kB/s |  63 kB     00:00 
(2/4): python3-elephant-0.6.2-3.fc30.noarch.rpm                                                                                                               681 kB/s | 456 kB     00:00 
(3/4): python3-quantities-0.12.2-4.fc30.noarch.rpm                                                                                                            421 kB/s | 163 kB     00:00 
(4/4): python3-neo-0.8.0-0.1.20190215git49b6041.fc30.noarch.rpm                                                                                               840 kB/s | 753 kB     00:00 
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 
Total                                                                                                                                                         884 kB/s | 1.4 MB     00:01 
Running transaction check 
Transaction check succeeded. 
Running transaction test 
Transaction test succeeded. 
Running transaction 
  Preparing        :                                                                                                                                                                      1/1 
  Installing       : python3-quantities-0.12.2-4.fc30.noarch                                                                                                                              1/4 
  Installing       : python3-igor-0.3-5.20150408git2c2a79d.fc30.noarch                                                                                                                    2/4 
  Installing       : python3-neo-0.8.0-0.1.20190215git49b6041.fc30.noarch                                                                                                                 3/4 
  Installing       : python3-elephant-0.6.2-3.fc30.noarch                                                                                                                                 4/4 
  Running scriptlet: python3-elephant-0.6.2-3.fc30.noarch                                                                                                                                 4/4 
  Verifying        : python3-elephant-0.6.2-3.fc30.noarch                                                                                                                                 1/4 
  Verifying        : python3-igor-0.3-5.20150408git2c2a79d.fc30.noarch                                                                                                                    2/4 
  Verifying        : python3-neo-0.8.0-0.1.20190215git49b6041.fc30.noarch                                                                                                                 3/4 
  Verifying        : python3-quantities-0.12.2-4.fc30.noarch                                                                                                                              4/4 
 
Installed: 
  python3-elephant-0.6.2-3.fc30.noarch   python3-igor-0.3-5.20150408git2c2a79d.fc30.noarch   python3-neo-0.8.0-0.1.20190215git49b6041.fc30.noarch   python3-quantities-0.12.2-4.fc30.noarch 
 
Complete!</div></div> </pre>
Notice how dnf even installed python3-igor, which isn’t a direct dependency of python3-elephant. 
<h2>DnfDragora: a graphical interface to DNF</h2>
While technical users may find dnf straightforward to use, it isn’t for everyone. <a href="https://src.fedoraproject.org/rpms/dnfdragora">Dnfdragora</a> addresses this issue by providing a graphical front end to dnf. 
<figure class="wp-block-image"><img src="http://www.sickgaming.net/blog/wp-content/uploads/2019/06/rpm-packages-explained.png" alt="" class="wp-image-28512" /><figcaption>dnfdragora (version 1.1.1-2 on Fedora 30) listing all the packages installed on a system.</figcaption></figure>
From a quick look, dnfdragora appears to provide all of dnf‘s main functions. 
There are other tools in Fedora that also manage packages. GNOME Software, and Discover are two examples. GNOME Software is focused on graphical applications only. You can’t use the graphical front end to install command line or terminal tools such as htop or weechat. However, GNOME Software does support the installation of <a href="https://fedoramagazine.org/getting-started-flatpak/">Flatpaks</a> and Snap applications which dnf does not. So, they are different tools with different target audiences, and so provide different functions. 
This post only touches the tip of the iceberg that is the life cycle of software in Fedora. This article explained what RPM packages are, and the main differences between using rpm and using dnf.
In future posts, we’ll speak more about:
<ul>
<li>The processes that are needed to create these packages</li>
<li>How the community tests them to ensure that they are built correctly</li>
<li>The infrastructure that the community uses to get them to community users in future posts. </li>
</ul>
</div>

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