What are Module Streams on RHEL?

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Module Streams are part of the Application Streams feature in RHEL. They allow multiple versions of software to be available and managed independently.

Key Concepts:

• Modules: Collections of RPM packages grouped.
• Streams: Different versions of a module (e.g., nodejs:10, nodejs:12).
• Profiles: Predefined sets of packages within a stream (e.g., default, development).

This system lets you install and manage different versions of software without conflicts.

1- List all available modules:

dnf module list

2- Filtering by a specific module:

dnf module list | grep nginx

or

dnf module list nginx

As we can see, the default stream (version) for the Nginx module is 1.14:

3- To change the Stream (to enable another Stream/version) for the Nginx module, for instance:

dnf module enable nginx:1.24

This sets the default stream for installation.

Inspect the module to confirm the default stream:

dnf module list nginx

If we try to install the Nginx now, the Nginx version will be 1.24:

dnf module install nginx

4- To revert the default stream for the Nginx module:

dnf module reset nginx

Inspect the module to confirm the default stream:

dnf module list nginx

As we can see, the default stream was reverted to the default – in this case, for instance, the stream (version) 1.14:

5- Regardless of the default stream of a module, we can also specify what stream (version) to install. Using Nginx, we can install Stream 1.22 by executing the following command:

dnf module install nginx:1.22

Common Mistakes with Modules Streams

1- Installing Without Enabling the Stream First:

• Mistake: Trying to install a module without enabling its stream.
• Fix: Always enable the desired stream before installing. Example:

dnf module enable php:7.4
dnf module install php:7.4

2- Forgetting to Reset Before Switching Streams:

• Mistake: Switching streams without resetting the module first.
• Fix: Use dnf module reset before enabling a new stream. Example:

dnf module reset php
dnf module enable php:8.0

3- Assuming the Default Stream Is What You Want:

• Mistake: Installing a module without checking which stream is the default.
• Fix: Always list the module to see available streams. Example to list all available Streams for the “php” module:

dnf module list php

4- Ignoring Profiles:

• Mistake: Installing a module without specifying a profile, leading to missing packages.
• Fix: Use the correct profile for your use case. You can, for example, check all Profiles a specific module has, and then choose to install the desired one. The “php” module has a lot of profiles:

Select the profile to install. Example:

dnf module install php:7.4/devel

5- Mixing RPMs from Different Streams:

• Mistake: Installing packages from different streams manually, causing conflicts.
• Fix: Stick to one stream per module and let DNF handle dependencies.

6- Not Cleaning Up After Removing a Module:

• Mistake: Removing a module but leaving the stream enabled.
• Fix: Reset the module after removal. Example:

dnf module remove --all php
dnf module reset php

Best Practices for Using Module Streams

1- Always Check Available Streams First:

Before installing any module, list its available streams and profiles. This helps you choose the correct version and avoid surprises. Example:

dnf module list nginx

2- Use Explicit Stream and Profile When Installing:

Avoid relying on defaults. Be precise.
This ensures consistency across systems and avoids unexpected behavior. Example:

dnf module install nginx:1.20/default

3- Reset Before Switching Streams:

If you need to change the stream, reset the module first. This clears previous stream selections and avoids conflicts. Example:

dnf module reset nginx
dnf module enable nginx:1.22

4- Use dnf module info for Details:

To understand what a stream or profile includes. Example:

dnf module info php:8.0

This shows package lists, profiles, and dependencies.

That’s it for now 🙂