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How RPM packages are made: the spec file

In the previous article on RPM package building, you saw that source RPMS include the source code of the software, along with a “spec” file. This post digs into the spec file, which contains instructions on how to build the RPM. Again, this article uses fpaste as an example.

Understanding the source code

Before you can start writing a spec file, you need to have some idea of the software that you’re looking to package. Here, you’re looking at fpaste, a very simple piece of software. It is written in Python, and is a one file script. When a new version is released, it’s provided here on Pagure: https://pagure.io/releases/fpaste/fpaste-0.3.9.2.tar.gz

The current version, as the archive shows, is 0.3.9.2. Download it so you can see what’s in the archive:

$ wget https://pagure.io/releases/fpaste/fpaste-0.3.9.2.tar.gz
$ tar -tvf fpaste-0.3.9.2.tar.gz
drwxrwxr-x root/root 0 2018-07-25 02:58 fpaste-0.3.9.2/
-rw-rw-r-- root/root 25 2018-07-25 02:58 fpaste-0.3.9.2/.gitignore
-rw-rw-r-- root/root 3672 2018-07-25 02:58 fpaste-0.3.9.2/CHANGELOG
-rw-rw-r-- root/root 35147 2018-07-25 02:58 fpaste-0.3.9.2/COPYING
-rw-rw-r-- root/root 444 2018-07-25 02:58 fpaste-0.3.9.2/Makefile
-rw-rw-r-- root/root 1656 2018-07-25 02:58 fpaste-0.3.9.2/README.rst
-rw-rw-r-- root/root 658 2018-07-25 02:58 fpaste-0.3.9.2/TODO
drwxrwxr-x root/root 0 2018-07-25 02:58 fpaste-0.3.9.2/docs/
drwxrwxr-x root/root 0 2018-07-25 02:58 fpaste-0.3.9.2/docs/man/
drwxrwxr-x root/root 0 2018-07-25 02:58 fpaste-0.3.9.2/docs/man/en/
-rw-rw-r-- root/root 3867 2018-07-25 02:58 fpaste-0.3.9.2/docs/man/en/fpaste.1
-rwxrwxr-x root/root 24884 2018-07-25 02:58 fpaste-0.3.9.2/fpaste
lrwxrwxrwx root/root 0 2018-07-25 02:58 fpaste-0.3.9.2/fpaste.py -> fpaste

The files you want to install are:

  • fpaste.py: which should go be installed to /usr/bin/.
  • docs/man/en/fpaste.1: the manual, which should go to /usr/share/man/man1/.
  • COPYING: the license text, which should go to /usr/share/license/fpaste/.
  • README.rst, TODO: miscellaneous documentation that goes to /usr/share/doc/fpaste.

Where these files are installed depends on the Filesystem Hierarchy Standard. To learn more about it, you can either read here: http://www.pathname.com/fhs/ or look at the man page on your Fedora system:

$ man hier

Part 1: What are we building?

Now that we know what files we have in the source, and where they are to go, let’s look at the spec file. You can see the full file here: https://src.fedoraproject.org/rpms/fpaste/blob/master/f/fpaste.spec

Here is the first part of the spec file:

Name: fpaste
Version: 0.3.9.2
Release: 3%{?dist}
Summary: A simple tool for pasting info onto sticky notes instances
BuildArch: noarch
License: GPLv3+
URL: https://pagure.io/fpaste
Source0: https://pagure.io/releases/fpaste/fpaste-0.3.9.2.tar.gz Requires: python3 %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

Name, Version, and so on are called tags, and are defined in RPM. This means you can’t just make up tags. RPM won’t understand them if you do! The tags to keep an eye out for are:

  • Source0: tells RPM where the source archive for this software is located.
  • Requires: lists run-time dependencies for the software. RPM can automatically detect quite a few of these, but in some cases they must be mentioned manually. A run-time dependency is a capability (often a package) that must be on the system for this package to function. This is how dnf detects whether it needs to pull in other packages when you install this package.
  • BuildRequires: lists the build-time dependencies for this software. These must generally be determined manually and added to the spec file.
  • BuildArch: the computer architectures that this software is being built for. If this tag is left out, the software will be built for all supported architectures. The value noarch means the software is architecture independent (like fpaste, which is written purely in Python).

This section provides general information about fpaste: what it is, which version is being made into an RPM, its license, and so on. If you have fpaste installed, and look at its metadata, you can see this information included in the RPM:

$ sudo dnf install fpaste
$ rpm -qi fpaste
Name : fpaste
Version : 0.3.9.2
Release : 2.fc30
...

RPM adds a few extra tags automatically that represent things that it knows.

At this point, we have the general information about the software that we’re building an RPM for. Next, we start telling RPM what to do.

Part 2: Preparing for the build

The next part of the spec is the preparation section, denoted by %prep:

%prep
%autosetup

For fpaste, the only command here is %autosetup. This simply extracts the tar archive into a new folder and keeps it ready for the next section where we build it. You can do more here, like apply patches, modify files for different purposes, and so on. If you did look at the contents of the source rpm for Python, you would have seen lots of patches there. These are all applied in this section.

Typically anything in a spec file with the % prefix is a macro or label that RPM interprets in a special way. Often these will appear with curly braces, such as %{example}.

Part 3: Building the software

The next section is where the software is built, denoted by “%build”. Now, since fpaste is a simple, pure Python script, it doesn’t need to be built. So, here we get:

%build
#nothing required

Generally, though, you’d have build commands here, like:

configure; make

The build section is often the hardest section of the spec, because this is where the software is being built from source. This requires you to know what build system the tool is using, which could be one of many: Autotools, CMake, Meson, Setuptools (for Python) and so on. Each has its own commands and style. You need to know these well enough to get the software to build correctly.

Part 4: Installing the files

Once the software is built, it needs to be installed in the %install section:

%install
mkdir -p %{buildroot}%{_bindir}
make install BINDIR=%{buildroot}%{_bindir} MANDIR=%{buildroot}%{_mandir}

RPM doesn’t tinker with your system files when building RPMs. It’s far too risky to add, remove, or modify files to a working installation. What if something breaks? So, instead RPM creates an artificial file system and works there. This is referred to as the buildroot. So, here in the buildroot, we create /usr/bin, represented by the macro %{_bindir}, and then install the files to it using the provided Makefile.

At this point, we have a built version of fpaste installed in our artificial buildroot.

Part 5: Listing all files to be included in the RPM

The last section of the spec file is the files section, %files. This is where we tell RPM what files to include in the archive it creates from this spec file. The fpaste file section is quite simple:

%files
%{_bindir}/%{name}
%doc README.rst TODO
%{_mandir}/man1/%{name}.1.gz
%license COPYING

Notice how, here, we do not specify the buildroot. All of these paths are relative to it. The %doc and %license commands simply do a little more—they create the required folders and remember that these files must go there.

RPM is quite smart. If you’ve installed files in the %install section, but not listed them, it’ll tell you this, for example.

Part 6: Document all changes in the change log

Fedora is a community based project. Lots of contributors maintain and co-maintain packages. So it is imperative that there’s no confusion about what changes have been made to a package. To ensure this, the spec file contains the last section, the Changelog, %changelog:

%changelog
* Thu Jul 25 2019 Fedora Release Engineering  - 0.3.9.2-3
- Rebuilt for https://fedoraproject.org/wiki/Fedora_31_Mass_Rebuild * Thu Jan 31 2019 Fedora Release Engineering  - 0.3.9.2-2
- Rebuilt for https://fedoraproject.org/wiki/Fedora_30_Mass_Rebuild * Tue Jul 24 2018 Ankur Sinha  - 0.3.9.2-1
- Update to 0.3.9.2 * Fri Jul 13 2018 Fedora Release Engineering  - 0.3.9.1-4
- Rebuilt for https://fedoraproject.org/wiki/Fedora_29_Mass_Rebuild * Wed Feb 07 2018 Fedora Release Engineering  - 0.3.9.1-3
- Rebuilt for https://fedoraproject.org/wiki/Fedora_28_Mass_Rebuild * Sun Sep 10 2017 Vasiliy N. Glazov  - 0.3.9.1-2
- Cleanup spec * Fri Sep 08 2017 Ankur Sinha  - 0.3.9.1-1
- Update to latest release
- fixes rhbz 1489605
...
....

There must be a changelog entry for every change to the spec file. As you see here, while I’ve updated the spec as the maintainer, others have too. Having the changes documented clearly helps everyone know what the current status of the spec is. For all packages installed on your system, you can use rpm to see their changelogs:

$ rpm -q --changelog fpaste

Building the RPM

Now we are ready to build the RPM. If you want to follow along and run the commands below, please ensure that you followed the steps in the previous post to set your system up for building RPMs.

We place the fpaste spec file in ~/rpmbuild/SPECS, the source code archive in ~/rpmbuild/SOURCES/ and can now create the source RPM:

$ cd ~/rpmbuild/SPECS
$ wget https://src.fedoraproject.org/rpms/fpaste/raw/master/f/fpaste.spec $ cd ~/rpmbuild/SOURCES
$ wget https://pagure.io/fpaste/archive/0.3.9.2/fpaste-0.3.9.2.tar.gz $ cd ~/rpmbuild/SOURCES
$ rpmbuild -bs fpaste.spec
Wrote: /home/asinha/rpmbuild/SRPMS/fpaste-0.3.9.2-3.fc30.src.rpm

Let’s have a look at the results:

$ ls ~/rpmbuild/SRPMS/fpaste*
/home/asinha/rpmbuild/SRPMS/fpaste-0.3.9.2-3.fc30.src.rpm $ rpm -qpl ~/rpmbuild/SRPMS/fpaste-0.3.9.2-3.fc30.src.rpm
fpaste-0.3.9.2.tar.gz
fpaste.spec

There we are — the source rpm has been built. Let’s build both the source and binary rpm together:

$ cd ~/rpmbuild/SPECS
$ rpmbuild -ba fpaste.spec
..
..
..

RPM will show you the complete build output, with details on what it is doing in each section that we saw before. This “build log” is extremely important. When builds do not go as expected, we packagers spend lots of time going through them, tracing the complete build path to see what went wrong.

That’s it really! Your ready-to-install RPMs are where they should be:

$ ls ~/rpmbuild/RPMS/noarch/
fpaste-0.3.9.2-3.fc30.noarch.rpm

Recap

We’ve covered the basics of how RPMs are built from a spec file. This is by no means an exhaustive document. In fact, it isn’t documentation at all, really. It only tries to explain how things work under the hood. Here’s a short recap:

  • RPMs are of two types: source and binary.
  • Binary RPMs contain the files to be installed to use the software.
  • Source RPMs contain the information needed to build the binary RPMs: the complete source code, and the instructions on how to build the RPM in the spec file.
  • The spec file has various sections, each with its own purpose.

Here, we’ve built RPMs locally, on our Fedora installations. While this is the basic process, the RPMs we get from repositories are built on dedicated servers with strict configurations and methods to ensure correctness and security. This Fedora packaging pipeline will be discussed in a future post.

Would you like to get started with building packages, and help the Fedora community maintain the massive amount of software we provide? You can start here by joining the package collection maintainers.

For any queries, post to the Fedora developers mailing list—we’re always happy to help!

References

Here are some useful references to building RPMs:


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5 cool music player apps

Do you like music? Then Fedora may have just what you’re looking for. This article introduces different music player apps that run on Fedora. You’re covered whether you have an extensive music library, a small one, or none at all. Here are four graphical application and one terminal-based music player that will have you jamming.

Quod Libet

Quod Libet is a complete manager for your large audio library. If you have an extensive audio library that you would like not just listen to, but also manage, Quod Libet might a be a good choice for you.

Quod Libet can import music from multiple locations on your disk, and allows you to edit tags of the audio files — so everything is under your control. As a bonus, there are various plugins available for anything from a simple equalizer to a last.fm sync. You can also search and play music directly from Soundcloud.

Quod Libet works great on HiDPI screens, and is available as an RPM in Fedora or on Flathub in case you run Silverblue. Install it using Gnome Software or the command line:

$ sudo dnf install quodlibet

Audacious

If you like a simple music player that could even look like the legendary Winamp, Audacious might be a good choice for you.

Audacious probably won’t manage all your music at once, but it works great if you like to organize your music as files. You can also export and import playlists without reorganizing the music files themselves.

As a bonus, you can make it look likeWinamp. To make it look the same as on the screenshot above, go to Settings / Appearance, select Winamp Classic Interface at the top, and choose the Refugee skin right below. And Bob’s your uncle!

Audacious is available as an RPM in Fedora, and can be installed using the Gnome Software app or the following command on the terminal:

$ sudo dnf install audacious

Lollypop

Lollypop is a music player that provides great integration with GNOME. If you enjoy how GNOME looks, and would like a music player that’s nicely integrated, Lollypop could be for you.

Apart from nice visual integration with the GNOME Shell, it woks nicely on HiDPI screens, and supports a dark theme.

As a bonus, Lollypop has an integrated cover art downloader, and a so-called Party Mode (the note button at the top-right corner) that selects and plays music automatically for you. It also integrates with online services such as last.fm or libre.fm.

Available as both an RPM in Fedora or a Flathub for your Silverblue workstation, install it using the Gnome Software app or using the terminal:

$ sudo dnf install lollypop

Gradio

What if you don’t own any music, but still like to listen to it? Or you just simply love radio? Then Gradio is here for you.

Gradio is a simple radio player that allows you to search and play internet radio stations. You can find them by country, language, or simply using search. As a bonus, it’s visually integrated into GNOME Shell, works great with HiDPI screens, and has an option for a dark theme.

Gradio is available on Flathub which works with both Fedora Workstation and Silverblue. Install it using the Gnome Software app.

sox

Do you like using the terminal instead, and listening to some music while you work? You don’t have to leave the terminal thanks to sox.

sox is a very simple, terminal-based music player. All you need to do is to run a command such as:

$ play file.mp3

…and sox will play it for you. Apart from individual audio files, sox also supports playlists in the m3u format.

As a bonus, because sox is a terminal-based application, you can run it over ssh. Do you have a home server with speakers attached to it? Or do you want to play music from a different computer? Try using it together with tmux, so you can keep listening even when the session closes.

sox is available in Fedora as an RPM. Install it by running:

$ sudo dnf install sox

Photo by Malte Wingen on Unsplash.