Chapter 4. Preparing the RHEL 7 system for an upgrade to RHEL 8

This section describes actions you need to perform on your RHEL 7 system before you can proceed with the upgrade to RHEL 8.

To prepare your RHEL 7 system for the upgrade to RHEL8, follow these steps:

  1. Migrate the GRUB Legacy boot loader to GRUB2

    After the upgrade, RHEL 7 still uses the GRUB Legacy boot loader. However, GRUB Legacy is not supported on RHEL 7 and later versions. Therefore, you must manually migrate the boot loader to GRUB2. For details, see the Upgrading from GRUB Legacy to GRUB 2 section in the RHEL 7 System Administrator’s Guide.

  2. Resolve potential problems with installed packages. For details, see Section 7.1, “Ensuring that installed packages match the current major RHEL version”.
  3. Adjust custom System V and Upstart scripts to systemd services.

    On a RHEL 7 system, systemd replaces Upstart as the init system. To use the features systemd provides, such as parallel startup of system services at boot time, manually convert legacy System V and Upstart scripts to systemd services. For details, see Converting traditional sysV init scripts to Red Hat Enterprise Linux 7 systemd unit files.

  4. Update paths to system directories in your scripts.

    On a RHEL 7 system, the /bin, /sbin, /lib, and /lib64 directories have been replaced by symbolic links to their corresponding directory in /usr. For example, on RHEL 8, /bin is a symbolic link to the /usr/bin/ directory.

    If you use scripts or applications that expect /bin, /sbin, /lib, and /lib64 to be real directories, adjust them accordingly. For example, you can update the scripts and applications to:

    • Use the paths in /usr, such as /usr/bin/
    • Accept that /bin, /sbin, /lib, and /lib64 are symbolic links instead of directories
  5. Update your YUM scripts and plug-ins to use the YUM 4 API.

    RHEL 8 no longer supports the Python API of YUM 3. If you use any scripts or YUM plug-ins that use the legacy API, migrate them to the YUM 4 API. For more information, see Notable changes to the YUM stack.

  6. If you miss certain packages after the upgrade, see the Section 7.3, “Installing missing packages after upgrading to RHEL 7” section in the Troubleshooting chapter.
  7. Review the Considerations in adopting RHEL 8 document and make additional changes to your system if needed.
  8. Update your system to the latest RHEL 7.9 version and reboot the host:

    # yum update
    # reboot
  9. Ensure that all your applications and services are configured and work as expected. For example, if you run a DNS server on the host, verify that the configuration is still valid after the upgrade and that the service works in the same way as it did before the upgrade.
  10. Follow the preparation steps described in the Preparing a RHEL 7 system for the upgrade chapter in the Upgrading from RHEL 7 to RHEL 8 document.