Choosing Software Collections for Alternative Python on CentOS: Decision Guide

Decision and Constraints

State the decision: install a newer Python version (e.g., 3.8) via Software Collections (SCL) to satisfy application requirements while keeping the base system Python untouched.

Constraints: preserve yum/dnf dependency integrity, keep SELinux enforcing, receive updates through official CentOS channels, and avoid breaking system tools that rely on the default python interpreter.

Supported Options Comparison

Option	Support Level	Ease of Upgrade	Impact on Base System
rh-python38 (SCL)	Fully supported in CentOS 7/8 repositories	yum update rh-python38*	Isolated under /opt/rh; no file conflicts
EPEL python38	Community maintained; may lag	yum update python38	Installs to /usr/bin/python38; can replace symlinks
Build from source	Self-maintained	Manual recompile	Files under /usr/local; risk of overwriting
Container image	Supported by image publisher	Pull new image	No host changes; requires runtime

Trade-offs

• SCL provides an isolated, fully supported runtime that can be enabled/disabled with scl enable.
• EPEL packages may conflict with base python libraries and require manual alternatives management.
• Building from source gives full control but adds maintenance burden and bypasses SELinux policies.
• Containers add overhead and require a container runtime, but give the strongest isolation.

Implementation Steps

1. Install the SCL repository (requires root or sudo):

   sudo yum install -y centos-release-scl

   Verify with rpm -q centos-release-scl; it should return a version string.
2. Install the desired collection (example for Python 3.8):

   sudo yum install -y rh-python38

   Check installation: rpm -q rh-python38.
3. Enable the collection for a shell session:

   scl enable rh-python38 bash

   Inside this session, python --version should show 3.8.x.
4. Run an application using the SCL without spawning a subshell:

   scl enable rh-python38 'python my_script.py'

   Alternatively, adjust the shebang to #!/usr/bin/env scl enable rh-python38 python or use a wrapper script.
5. Confirm base system Python remains unchanged:

   /usr/bin/python --version

   Should still output the default (e.g., 2.7.5 on CentOS 7 or 3.6.8 on CentOS 8).

Verification

• Repository presence: rpm -q centos-release-scl returns a version.
• Package installed: rpm -q rh-python38.
• Enabled version: scl enable rh-python38 'python --version' yields Python 3.8.x.
• Base interpreter untouched: /usr/bin/python --version shows original.

Limitations

• SCL packages are only provided for CentOS Linux 7 and 8; CentOS Stream 9 uses modular streams, so rh-python38 may not be available.
• Enabling an SCL does not change system-wide alternatives; each invocation must use scl enable or a modified shebang.
• Updates to the collection follow the SCL release schedule; major version jumps require a new package (e.g., rh-python39).

Rollback (if needed)

Because installing the SCL adds files under /opt/rh and modifies the package database, you can remove it:

sudo yum remove -y rh-python38

Optionally remove the SCL repository package if no other collections are needed:
sudo yum remove -y centos-release-scl

After removal, verify that /usr/bin/python still points to the system interpreter and that no application depends on the removed runtime.