Migrating from CentOS to Rocky Linux: A Practical Conversion Guide

Why CentOS Is No Longer an Option

CentOS Linux 8 reached end of life on December 31, 2021 — years earlier than expected. CentOS Stream is a rolling release that sits upstream of RHEL, not downstream, making it unsuitable as a production replacement. CentOS 7 reached end of life on June 30, 2024.

Rocky Linux fills the gap: it's a downstream RHEL rebuild, binary-compatible, community-maintained, and committed to the long-term stable release model CentOS used to provide. This guide covers converting existing CentOS 8 or CentOS Stream 8 systems to Rocky Linux 8, and migrating CentOS 7 systems to Rocky Linux 9 via a fresh OS upgrade path.

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Migration vs. Fresh Install

You have two options:

In-place conversion (CentOS 8 → Rocky Linux 8): The migrate2rocky script swaps out the distribution packages while preserving all installed software, configuration, and data. Suitable for servers you can't easily reprovisioned.

Fresh install + restore (CentOS 7 → Rocky Linux 9): Since the major version jump changes too much (Python 2→3, systemd behavior, libraries), a fresh Rocky Linux 9 install with configuration/data migration is often safer and cleaner.

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Pre-Migration Checklist

Before running any migration:

# 1. Snapshot or backup the system (VM snapshot, disk backup)
# This is non-negotiable. If migration fails mid-way, you need a restore point.

# 2. Check current OS version
cat /etc/centos-release
cat /etc/os-release

# 3. Check available disk space (need ~3GB for package downloads)
df -h /

# 4. Check for third-party repositories that may conflict
yum repolist
ls /etc/yum.repos.d/

# 5. Note what's currently running
systemctl list-units --type=service --state=running > /tmp/services-before.txt
yum list installed > /tmp/packages-before.txt

# 6. Check kernel version
uname -r

# 7. Disable or note any SELinux policies you've customized
getenforce
sestatus

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Migrating CentOS 8 / CentOS Stream 8 to Rocky Linux 8

Step 1: Download migrate2rocky

# Download the official migration script
curl -O https://raw.githubusercontent.com/rocky-linux/rocky-tools/main/migrate2rocky/migrate2rocky.sh

# Verify it's what you expect — review it before running
less migrate2rocky.sh

# Make executable
chmod +x migrate2rocky.sh

Step 2: Run the Migration

# Run migration (takes 10-30 minutes depending on package count)
sudo bash migrate2rocky.sh -r

# The -r flag means: convert this system to Rocky Linux
# The script will:
# 1. Add Rocky Linux GPG keys and repos
# 2. Remove CentOS-specific packages
# 3. Install Rocky Linux equivalents
# 4. Update all packages to Rocky Linux versions

Monitor progress — the script is verbose and will log what it's replacing. It will stop and report if it encounters an unresolvable conflict.

Step 3: Reboot

sudo reboot

Step 4: Verify Migration

# Confirm you're on Rocky Linux
cat /etc/rocky-release
cat /etc/os-release

# Example output:
# Rocky Linux release 8.x (Green Obsidian)
# NAME="Rocky Linux"

# Check kernel
uname -r

# Verify no CentOS packages remain
rpm -qa | grep centos

# Check all repos are Rocky Linux
yum repolist

# Compare running services to pre-migration list
systemctl list-units --type=service --state=running > /tmp/services-after.txt
diff /tmp/services-before.txt /tmp/services-after.txt

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Handling Third-Party Repositories

The migration script may have disabled third-party repos that had CentOS-specific URLs. Check and re-enable as needed:

# Check disabled repos
yum repolist disabled

# Common repos that need updating:
# EPEL — re-enable for Rocky Linux 8
sudo dnf install https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm

# IUS, Remi, etc. — find their Rocky Linux repo URLs
# Check the repo's website for Rocky Linux / RHEL 8 packages

# Re-enable a repo
sudo yum-config-manager --enable <repo-id>

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Migrating CentOS 7 to Rocky Linux 9 (Fresh Install Path)

Because CentOS 7 is EOL and the jump to Rocky 9 spans two major versions, the safest approach is a fresh installation with data migration.

Step 1: Document the Current System

# Save installed package list
rpm -qa --qf "%{NAME}\n" | sort > /tmp/packages-centos7.txt

# Save service states
systemctl list-unit-files --type=service | grep enabled > /tmp/services-centos7.txt

# Save network config
ip addr > /tmp/network-config.txt
cat /etc/sysconfig/network-scripts/ifcfg-* >> /tmp/network-config.txt

# Save crontabs
crontab -l > /tmp/root-crontab.txt 2>/dev/null
for user in $(awk -F: '{ print $1 }' /etc/passwd); do
    crontab -u "$user" -l 2>/dev/null | grep -v "^no crontab" && echo "--- $user ---"
done > /tmp/user-crontabs.txt

# Back up application data and configs
rsync -av /etc/ /backup/etc/
rsync -av /var/www/ /backup/var-www/ 2>/dev/null
rsync -av /home/ /backup/home/

Step 2: Install Rocky Linux 9

Install from the official Rocky Linux 9 ISO onto the target system or provision a new VM with Rocky Linux 9.

Step 3: Re-provision the System

# On the new Rocky Linux 9 system:

# Install comparable packages
# Match your package list, substituting for any CentOS 7 packages
# that have been renamed or replaced

# Enable EPEL for Rocky Linux 9
sudo dnf install https://dl.fedoraproject.org/pub/epel/epel-release-latest-9.noarch.rpm

# Restore data
rsync -av /backup/home/ /home/
rsync -av /backup/var-www/ /var/www/

# Restore configs (review before blindly copying — configs may have changed format)
# Copy selectively, e.g.:
cp /backup/etc/nginx/nginx.conf /etc/nginx/nginx.conf
cp /backup/etc/my.cnf /etc/my.cnf

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Post-Migration Validation

For both in-place and fresh installs:

# 1. Verify SELinux status
getenforce   # Should be Enforcing on production systems

# 2. Check for packages with unresolved dependencies
dnf check

# 3. Verify all expected services are running
systemctl status nginx mysql postgresql   # adjust for your stack

# 4. Test application endpoints
curl -I http://localhost/
curl -f http://localhost/health

# 5. Check logs for errors post-migration
journalctl -p err --since "1 hour ago"

# 6. Verify firewall rules
firewall-cmd --list-all

# 7. Run your test suite or smoke tests

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Rocky Linux vs AlmaLinux: Which to Choose

Both Rocky Linux and AlmaLinux are CentOS replacements with RHEL binary compatibility. The choice is mostly organizational:

	Rocky Linux	AlmaLinux
Governance	Rocky Enterprise Software Foundation	AlmaLinux OS Foundation
Backing	Community	CloudLinux
RHEL compatibility	1:1 binary	1:1 binary (ABI compatible)
Certifications	In progress	Some achieved
Kernel Live Patching	Via ELRepo	Via TuxCare/AlmaLinux

Both are viable. Pick based on which community, commercial support agreements, or existing internal experience fits your organization.

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Quick Reference

# Post-migration: update everything to latest
sudo dnf update -y

# Install development tools
sudo dnf groupinstall "Development Tools" -y

# Enable CodeReady Linux Builder (equivalent to CentOS PowerTools)
sudo dnf config-manager --set-enabled crb
sudo dnf install crb-release -y   # alternative method

# Check Rocky Linux version
cat /etc/rocky-release

# Subscribe to Rocky Linux security announcements
# https://lists.resf.org/archives/list/[email protected]/

Rocky Linux's strength is exactly what CentOS 8 had before EOL: a stable, freely available RHEL-compatible platform. If your team knows RHEL or CentOS, Rocky Linux requires essentially no retraining.