Building packages in linux

How to create a Linux RPM package

This article shows you how to package a script into an RPM file for easy installation, updating, and removal from your Linux systems. Before I jump into the details, I’ll explain what an RPM package is, and how you can install, query, remove, and, most importantly, create one yourself.

• What an RPM package is.
• How to create an RPM package.
• How to install, query, and remove an RPM package.

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What is an RPM package?

RPM stands for Red Hat Package Manager. It was developed by Red Hat and is primarily used on Red Hat-based Linux operating systems (Fedora, CentOS, RHEL, etc.).

An RPM package uses the .rpm extension and is a bundle (a collection) of different files. It can contain the following:

• Binary files, also known as executables ( nmap , stat , xattr , ssh , sshd , and so on).
• Configuration files ( sshd.conf , updatedb.conf , logrotate.conf , etc.).
• Documentation files ( README , TODO , AUTHOR , etc.).

The name of an RPM package follows this format:

Some packages also include a shorthand version of the distribution they were built for, such as:

How to create an RPM package

You’ll need the following components to build an RPM package:

• A workstation or a virtual machine running an RPM-based distribution, such RHEL or Fedora.
• Software to build the package.
• Source code to package.
• SPEC file to build the RPM.

Installing the required software

The following packages need to be installed to build the RPM package:

$ sudo dnf install -y rpmdevtools rpmlint

After installing rpmdevtools , create the file tree you need to build RPM packages:

You build RPM packages as a normal (not root) user, so your build environment is placed into your home directory. It contains this directory structure:

rpmbuild/ ├── BUILD ├── RPMS ├── SOURCES ├── SPECS └── SRPMS

• The BUILD directory is used during the build process of the RPM package. This is where the temporary files are stored, moved around, etc.
• The RPMS directory holds RPM packages built for different architectures and noarch if specified in .spec file or during the build.
• The SOURCES directory, as the name implies, holds sources. This can be a simple script, a complex C project that needs to be compiled, a pre-compiled program, etc. Usually, the sources are compressed as .tar.gz or .tgz files.
• The SPEC directory contains the .spec files. The .spec file defines how a package is built. More on that later.
• The SRPMS directory holds the .src.rpm packages. A Source RPM package doesn’t belong to an architecture or distribution. The actual .rpm package build is based on the .src.rpm package.

A .src.rpm package is very flexible, because it can be built and re-built on every other RPM-based distribution and architecture.

You’re now familiar with what each directory holds, so now create a simple script to distribute:

$ cat > hello.sh #!/bin/sh echo "Hello world" EOF

This creates a shell script called hello.sh , which prints «Hello world» to the terminal. It’s simple, but it’s enough to demonstrate packaging.

Place the script in the designated directory

To build a package for your script, you must put your script in the directory that the RPM build system expects it to be in. Create a directory for it, using semantic versioning as most projects do, and then move hello.sh into it:

$ mkdir hello-0.0.1 $ mv hello.sh hello-0.0.1

Most source code is distributed as an archive, so use the tar command to create an archive file:

$ tar --create --file hello-0.0.1.tar.gz hello-0.0.1

Then move the tarball you’ve just created into the SOURCES directory:

Create a .spec file

An RPM package is defined by a .spec file. The syntax of a .spec file is strict, but rpmdev can generate a boilerplate file for you:

This generates a file called hello.spec , which you must move to the SPECS directory. Run tree ~/rpmbuild to see what the directory structure looks like:

/home/tux/rpmbuild/ ├── BUILD ├── BUILDROOT ├── RPMS ├── SOURCES │ └── hello-0.0.1.tar.gz ├── SPECS │ └── hello.spec └── SRPMS

The generated hello.spec file provides a good starting point, but it doesn’t have any specific information about what you’re building. The generated .spec file assumes that I am going to compile and build software.

You’re packaging a Bash script, so there’s some simplification you can do. For instance, there’s no Build process because there’s no code to compile. I’ve added BuildArch: noarch because this package is valid for 32-bit, 64-bit, Arm, and any other CPU architecture that runs Bash.

I’ve also added Requires: bash so that the package ensures that Bash is installed. This simple «hello world» script runs on any shell, of course, but that’s not true for all scripts, so this is a good way to demonstrate dependencies.

Name: hello Version: 0.0.1 Release: 1% Summary: A simple hello world script BuildArch: noarch License: GPL Source0: %-%.tar.gz Requires: bash %description A demo RPM build %prep %setup -q %install rm -rf $RPM_BUILD_ROOT mkdir -p $RPM_BUILD_ROOT/% cp %.sh $RPM_BUILD_ROOT/% %clean rm -rf $RPM_BUILD_ROOT %files %/%.sh %changelog * Sun Nov 18 2020 Valentin Bajrami - 0.0.1 - First version being packaged

As you can tell, there are a lot of shortcuts in .spec files. They’re called macros, and there’s an excellent list of what’s available in the Fedora packaging documentation. It’s important to use macros in your .spec files. They help ensure consistency across all RPM systems, they help you avoid mistakes in filenames and version numbering, and they make it easier to update the .spec file when you release a new version of your script.

For example, it’s required that you specify exactly which files are installed under the %files section. Here I’ve explicitly put the following line:

This works because I want the script to go to % (which is a macro that translates to /usr/bin by default, but is configurable when users want to install to a different location, such as /usr/local/bin ). You can verify macro values by running:

• % name of the package (as defined in the Name: field)
• % version of the package (as defined in the Version: field)
• % shared data ( /usr/sbin by default)
• % configuration directory ( /etc by default)

Checking the .spec file on error (rpmlint)

The rpmlint command can find errors in .spec files:

$ rpmlint ~/rpmbuild/SPECS/hello.spec SPECS/hello.spec: W: no-%build-section SPECS/hello.spec: W: invalid-url Source0: hello-0.0.1.tar.gz 0 packages and 1 specfiles checked; 0 errors, 2 warnings.

There are 2 errors reported, but they’re both acceptable. There’s no code to build, so there’s no need for a %build section, and the source archive is a local file and has no network URL.

Building the package (rpmbuild)

To build the RPM package, use the rpmbuild command. Earlier in this tutorial, I mentioned the difference between the .src.rpm (Source RPM package) and the .rpm package.

To create the .src rpm package:

$ rpmbuild -bs ~/rpmbuild/SPECS/hello.spec

The flags -bs have the following meanings:

To create the binary .rpm package:

$ rpmbuild -bb ~/rpmbuild/SPECS/rm-ssh-offendingkey.spec

The flags -bb have the following meanings:

After the build process is finished, you have the following directory structure:

$ tree ~/rpmbuild/ /home/tux/rpmbuild/ ├── BUILD │ └── hello-0.0.1 │ ├── hello.sh ├── BUILDROOT ├── RPMS │ └── noarch │ └── hello-0.0.1-1.el8.noarch.rpm ├── SOURCES │ └── hello-0.0.1.tar.gz ├── SPECS │ └── hello.spec └── SRPMS

Installing the RPM package

After a successful build of the package, you can install the RPM package using the dnf command:

$ sudo dnf install ~/rpmbuild/RPMS/noarch/hello-0.0.1-1.el8.noarch.rpm

It can alternately be installed with the rpm command directly:

$ sudo rpm -ivh ~/rpmbuild/RPMS/noarch/hello-0.0.1-1.el8.noarch.rpm

Verify the package has been installed

To verify the package has correctly been installed, run the following command:

$ rpm -qi hello Name : hello Version : 0.0.1 Release : 1 Architecture: noarch Install Date: Mon 09 Nov 2020 01:29:51 AM CET Group : Unspecified Size : 294 License : GPL Signature : (none) Source RPM : hello-0.0.1-1.el8.src.rpm Build Date : Mon 09 Nov 2020 01:08:14 AM CET Build Host : slimmerAI Summary : A simple hello world script Description : A demo RPM build

The %changelog entry of a package can be viewed, too:

$ rpm -q hello --changelog * Sun Nov 08 2020 Valentin Bajrami - 0.1 - First version being packaged

See what’s in the RPM package

It’s easy to see which files an RPM package contains:

$ rpm -ql hello /usr/bin/hello.sh

Removing the RPM package

Removing the package from the system is just as easy as installing it. You can use the dnf command:

Or the rpm command directly:

$ sudo rpm --verbose --erase hello

Final thoughts

In this document, I covered the very basics of packaging, including how to build, install, and remove an RPM package from your system. The .spec file can get very complicated as you build more advanced software, but you can read through real-world examples on public software repositories, such as src.fedoraproject.org, to learn more.

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