The old Debian 11 recipe used the original ConfigServer download and presented sample module-test output as a success result. Do not use that recipe for a new server. Debian 11's Debian LTS period ended on 31 August 2026; any third-party extended support arrangement is separate. Debian lifecycle
Why the installation instructions changed
The original CSF developer no longer maintains it. cPanel documents a maintained cPanel-specific version, but its package is intended for cPanel systems; that does not establish support for a standalone Debian 11 host. cPanel guide, repository requirements
Aetherinox publishes a separate CSF fork with a generic installer and Debian/Ubuntu dependency guidance. Its documentation is a primary source for that fork, but it does not extend Debian 11's OS lifecycle or establish that your kernel/network stack was tested. Aetherinox installer, dependencies
Inventory before migrating
Record the distribution/version, network interfaces, current firewall manager, required listening services and provider firewall rules. Preserve the existing configuration and how to restore it. Include IPv6, outbound email/DNS, monitoring and any container/networking policy rather than only inbound web ports.
If the server uses nftables, its read-only ruleset query is:
sudo nft list ruleset
The project reference distinguishes listing from add/delete/flush commands. Do not flush the live ruleset while collecting evidence. nftables reference
A CSF installation can involve other backends and management layers; record those through their own documented reporting tools. Avoid enabling a competing rules manager just to inspect the host.
Install the Aetherinox fork only after compatibility checks
Review the fork's dependency and kernel/backend requirements against your chosen supported Debian release. Preserve the existing firewall and configuration, arrange console access and choose a clean working directory. Its download guide publishes:
curl -O https://download.configserver.dev/csf.tgz
Inspect the downloaded release and installer, then follow that fork's extraction and generic-install instructions. Do not overwrite an existing cPanel-managed CSF installation as if it were a generic host. Download procedure, installer routes
Run the documented diagnostic tests and retain their actual output. A module-test success does not verify your allowed/denied traffic policy or prove the firewall cannot lock you out. Diagnostic procedure
Choose and stage the replacement
For a new standalone server, use a maintained firewall workflow documented for the selected supported OS, or a fork whose maintainer, releases, signing/update process and OS support you have independently checked. For an existing server, recreate the required policy on a test host and identify rules that no longer serve a purpose.
Prepare console access and a rollback policy. Stage access for the management connection before applying restrictive rules. Test allowed and denied connections from another host, including IPv4/IPv6 and required outgoing services, and verify persistence through an agreed reboot test.
Existing Debian 11 systems
If immediate migration is not possible, document the explicit OS support arrangement and firewall update ownership. Avoid installing an old dependency list that includes a mail server without understanding the impact on an existing mail service. Preserve access while planning migration; do not uninstall the current firewall before the replacement and recovery route are ready.
The outcome to seek is a maintained, verified policy with a working update and recovery path. No module check, firewall install or live connectivity test was performed for this review.