Migration guide

Migrate CentOS 7 to RHEL 9

Q: How do I show that the RHEL 9 host matches the old one?

With the parity report. vrtmv verify checks the rebuilt host against the plan, from its package database and the carried configuration paths, and exits non-zero on any parity gap, so cutover can be gated on it. Keep the source inventory, the plan and the report with the change record.

For a team that wants a vendor behind the new hosts, RHEL 9 is the target. Red Hat's supported route from CentOS 7 changes the same live machine three times: convert2rhel turns it into RHEL of the same major release, then Leapp upgrades it one major release at a time. Each step is a reboot, a pre-upgrade report to clear, and a point at which the host can stop booting.

vrtmv reads the CentOS 7 host once and plans a fresh RHEL 9 host from it, so the old machine is never changed and stays there to fall back to. What differs from a free rebuild is mostly access: RHEL 9's repositories need a subscription before anything installs.

Where CentOS 7 stands

CentOS 7 reached its end of life in June 2024.

Packages that change name

Of the packages the Index translates for this move, these arrive on RHEL 9 under another name. vrtmv installs the new name and carries the configuration across; nothing on the old host is renamed by hand.

authconfig becomes authselect. EL8 removed authconfig.
dhclient becomes dhcp-client.
dhcp becomes dhcp-server.
iptables and iptables-services become iptables-nft and iptables-nft-services.
java-1.8.0-openjdk and java-1.8.0-openjdk-devel become java-17-openjdk and java-17-openjdk-devel.
mailx becomes s-nail. EL9 removed the mailx package (it survives on EL8).
ntp becomes chrony. EL8/EL9 removed ntp.
ntpdate becomes chrony. EL8/EL9 removed ntpdate.
pkgconfig becomes pkgconf. EL8 replaced pkgconfig with pkgconf, which provides the pkg-config command and declares Provides: pkgconfig for compatibility.

Services that change

network.service is replaced by NetworkManager.service: the enabled service is moved to its successor, not left pointing at a unit that no longer exists.
ntpd.service is replaced by chronyd.service: the enabled service is moved to its successor, not left pointing at a unit that no longer exists.

Databases on each side

PostgreSQL: 9.2 by default on CentOS 7, 13 by default and 15, 16, 18 as module streams on RHEL 9. The data moves by an in-place pg_upgrade or a dump and restore, with the database stopped.

Repositories

Every RHEL 9 repository needs a subscription: AppStream, BaseOS, CodeReady Builder and Supplementary. The host has to be registered before the rebuild can install anything. Vendor repositories the source used are named in the plan, not silently enabled.

What needs your decision

vrtmv does not guess at these. Each one is a line on the plan's punch list, for you to settle before the rebuild runs.

Subscriptions. Each new host needs a RHEL entitlement, and registering it (with subscription-manager or an activation key) is part of the build, not an afterthought.
python and python-libs have no package on RHEL 9. Source must port to Python 3 before migration.
authconfig to authselect is not a drop-in replacement; the plan lists its settings for review.
ntp to chrony is not a drop-in replacement; the plan lists its settings for review.
ntpdate to chrony is not a drop-in replacement; the plan lists its settings for review.

What the parity run showed

vrtmv's conformance run for this pair read the inventory from a CentOS 7 system, planned the move and applied the plan to a fresh RHEL 9 system. All 16 packages the plan promised were installed on the target, and the one carried configuration file landed. Your parity report gives the same accounting for your own hosts.

Should this become a container?

Usually not. A container image runs one command, with no init and no scheduler, on the kernel of the machine it runs on. A CentOS 7 host that runs one long-lived service, keeps its data in directories you can mount as volumes and reads its config from files is a candidate for one; start the image and test that service before you plan a cutover on it. A host that runs several services, keeps a database on its own disk or runs cron jobs is better rebuilt as a RHEL 9 machine, which is what vrtmv does by default.

Before you choose, vrtmv assess runs its container feasibility checks on the source (kernel modules, the entrypoint, local state, scheduled jobs and software no package installed) and prints what each one found. The full fit lists, and what breaks after the image runs.

How vrtmv does it

vrtmv reads the CentOS 7 host without an agent and changes nothing on it. The Index translates its packages, services and settings to RHEL 9, and the plan lists every change and every decision before anything runs. The new host is built from that plan, and the parity report compares it with the old one, so you can show an auditor what came across.

Questions about this move

Does vrtmv upgrade CentOS 7 to RHEL 9 in place?

No. vrtmv reads the CentOS 7 host without an agent and changes nothing on it. It builds a fresh RHEL 9 host from the plan, so the old host keeps running until you cut over, and it stays your way back.

Which packages change name on RHEL 9?

11 of the packages the Index translates for this move arrive on RHEL 9 under another name, for example authconfig becomes authselect and dhclient becomes dhcp-client. vrtmv installs the new name and carries the configuration across, and the plan lists each one.

Does RHEL 9 need a subscription?

Yes. Every RHEL 9 repository needs one: AppStream, BaseOS, CodeReady Builder and Supplementary. The new host has to be registered before the rebuild can install anything.

Is CentOS 7 still supported?