Migrating From CentOS 8 to Rocky Linux—A Straight‑Ahead Playbook
You’ll learn how to move your existing CentOS 8 box into the new Rocky Linux ecosystem without losing data or having to rebuild services from scratch. No fancy scripts, just a few hands‑on steps that keep the core system intact and let you enjoy Rocky’s upstream‑compatible packages.
1 – Back It All Up
Why bother? A full backup is your safety net; you’ll need it if something goes wrong or if you decide to roll back. I’ve seen servers get stuck after a bad update that broke the init system, so start by:
sudo rsync -avxHAX / /mnt/backup/
rsync keeps ownership and permissions intact; add --delete only when you’re sure you want to mirror everything.
2 – Create a Live‑USB of the Latest Rocky
Download the ISO from the official site and write it to a USB stick with:
sudo dd if=Rocky-8.6-x86_64-dvd1.iso of=/dev/sdX bs=4M status=progress && sync
Replace /dev/sdX with your real device; double‑check before running dd.
3 – Boot Into the Live Environment
Power on, hit F12 (or whatever key your BIOS uses) and boot from USB. Pick “Install Rocky Linux” but don’t proceed to install yet.
4 – Replace CentOS Packages With Rocky Repositories
Mount your original root partition:
sudo mount /dev/mapper/centos8-root /mnt/oldroot
Enter a chroot so you’re running commands in the old system’s context:
sudo chroot /mnt/oldroot
Now swap out CentOS repositories for Rocky:
1. Remove existing repo files:
rm -f /etc/yum.repos.d/*.repo
2. Install the Rocky repos package:
dnf install https://dl.rockylinux.org/pub/rocky/rhel-8/x86_64/os/Packages/r/rpm-macros-4.14-2.el8.noarch.rpm
3. Import Rocky GPG keys and enable the repos by adding a new file:
cat > /etc/yum.repos.d/rocky.repo <<EOF [AppStream] name=Rocky Linux 8 AppStream baseurl=https://dl.rockylinux.org/pub/rocky/rhel-8/AppStream/x86_64/os/ enabled=1 gpgcheck=1 [BaseOS] name=Rocky Linux 8 BaseOS baseurl=https://dl.rockylinux.org/pub/rocky/rhel-8/BaseOS/x86_64/os/ enabled=1 gpgcheck=1 EOF
The reason for this repo swap is that Rocky’s packages are binary‑compatible with CentOS, so you’ll preserve all installed software.
5 – Clean Old Packages and Reinstall
Exit chroot (exit), unmount the old root, then boot from the live USB again. This time choose “Rescue a broken system” to drop into a minimal shell:
chroot /mnt/oldroot dnf clean all dnf distro-sync
distro‑sync pulls in the Rocky versions of every package that already exists, updating libraries and binaries while keeping configuration files. If you’ve got custom packages from third‑party repos, double‑check they’re still enabled or add them back.
6 – Verify System Integrity
Back into your regular shell:
cat /etc/os-release | grep PRETTY_NAME
You should see “Rocky Linux 8.x”. Next, check that critical services are running:
systemctl list-units --type=service | grep -E 'httpd|sshd|firewalld'
If any of them are failed, read their logs with journalctl -u <service>. I’ve seen the Apache service fail after a mismatched module version—just reinstall the module package.
7 – Remove CentOS‑Specific Tools
CentOS shipped some legacy utilities (like yum wrapper scripts) that Rocky no longer needs. Clean them up to avoid confusion:
dnf remove yum*
You’ll keep dnf, which is now the default.
8 – Reboot Into Rocky
Remove the USB, let the system boot from disk. If everything boots and your services are healthy, you’re done. If not, roll back using your backup or the last known good snapshot (if you use LVM snapshots).
That’s it—no full reinstall required, just a repository swap, a distro‑sync, and a sanity check.
