Migration Guide
This page was created by PhilSchaffner and addresses migration from older to newer CentOS versions, and from other Enterprise Linux distributions based on the same set of upstream source packages to CentOS. Contributions by others are welcome.
- General considerations regarding migration:
A fresh install is generally strongly preferred over an upgrade.
- Be sure you have a good (bootable or restorable) backup before doing anything major to a system you care about.
- It is often helpful to have a bootable linux system on a separate set of partitions or better yet a separate disk. This can serve as a fall-back or rescue system, as well as an on-line backup. Disk space is cheap compared to sysadmin time.
Migrations from other systems based on the same set of upstream source packages should be relatively straight-forward. See FAQ/CentOS3 Question #5 "How do I migrate a system from WBEL-3 (White Box Enterprise Linux) to CentOS 3?" for example.
- You may want to upgrade the operating system parts of the filesystem and leave user directories, such as /home in place. If you do leave the old user home directories in place expect some problems with the GNOME/KDE menus and other desktop items. It may be preferable to create new user accounts and mount the old directories somewhere else in the filesystem for reference, copying, or linking user's material after the migration.
- If you decide to do an upgrade anyway...
- Back up anything you care about.
Remember - A fresh install is generally strongly preferred over an upgrade.
- Clean up as much as possible before the upgrade, removing any RPMS you do not need, or that you know will be obsoleted.
- Do an anaconda upgrade. Yum upgrades, or "live" upgrades with other package managers, MAY be possible but are often more problematic - particularly with regard to glibc and kernel/drivers.
- Upgrades from the immediately preceeding version are more likely to be successful than upgrades across multiple versions. For example, if you are running CentOS 3 and want to upgrade to CentOS 5, first upgrade to the latest release of CentOS 4 (version 4.4 as of this writing).
Upgrades from systems other than the latest CentOS (WhiteBox, RHEL, TaoLinux, ...) may be possible but will also require more work cleaning up afterwards. Consider migrating to the corresponding CentOS release before upgrading.
- After upgrading use "rpm -qa --last", preferably redirected to a file or piped to "less", to find packages that were not updated. Left-over packages will be at the end of the output and will have dates earlier than the date of the upgrade.
- Remove any left-over packages that are not needed.
- If you find left-over packages that have version numbers greater than or equal to the current-release CentOS packages, use "rpm -Uvh --oldpackage foo-1.2-3.i386.rpm ... " (or possibly the ugly "rpm -Uvh --force ..." in a pinch) to get CentOS versions of packages that may have had lower or identical version numbers to replace the obsolete packages.
Find/build ELx/CentOSx (where x=2,3,4,5) versions of remaining required/desired packages. ATrpms, RPMforge (Dag/Dries), and EPEL (Fedora Extras for EL) Repositories all have ELx packages that work with the corresponding CentOS versions. KaranbirSingh rebuilds Fedora Extras and some other packages for CentOS. Things that can't be found there can often be rebuilt from Fedora core or Fedora Extras src.rpm packages, or perhaps even the FC binaries used directly if you are feeling lucky (not recommended). Best to start with the packages at the Fedora/RH level from which the corresponding EL distro was forked. For EL5/CentOS5 this was an FC6 test version.
- If older packages do not have versions that work with the current OS version, consider using virtualization to support them by running older OS versions uder the current release. Viable options include VMware and Xen.
Always beware when using/mixing 3rd-party repos. The yum protectbase or priorities plugins are your friends. Although both can be used together, the priorities plugin provides more functionality and using protectbase is unnecessary if the priorities plugin is configured properly. See PackageManagement/Yum/ProtectBase and PackageManagement/Yum/Priorities.
- Enjoy!
- If upgrading, consider first "cloning" the system and upgrading the clone.
- As root, create the new partitions as desired - root, boot, home, swap - assume for example /dev/hde1 ,2, 3, 4...
- Make file systems
# mke2fs -j -L /clone_boot /dev/hdb1 # mke2fs -j -L /clone /dev/hde2 # mkswap -L SWAP-hde3 /dev/hde3 # mke2fs -j -L /clone_home /dev/hde5 # mke2fs -j -L /clone_data /dev/hde6
- Make a mountpoint for the clone, say /clone
# mkdir /clone
- Mount the partition that is to be the new root on /clone, make other mount points, mount all new partitions
# mount /dev/hde2 /clone # mkdir /clone/boot /clone/home /clone/data # mount /dev/hde1 /clone/boot # mount /dev/hde5 /clone/home # mount /dev/hde6 /clone/data
- Do the clone operation
# tar clf - /boot | tar xf - -C /clone # tar clf - /home | tar xf - -C /clone # tar clf - / | tar xf - -C /clone
- Edit /etc/fstab, /boot/grub/grub.conf adding entries for the clone partitions and boot stanzas
- Edit /clone/etc/fstab, /clone/boot/grub/grub.conf adding entries for the original partitions and boot stanzas
- Test-boot both systems before proceeding.
- Perform the upgrade on the clone system and write grub to the boot partition rather than the MBR
- Boot the original OS and update the grub boot stanza for the new OS - formerly clone.
- Boot the new OS. Optionally, make the new OS grub the default (preferably after testing)
# grub-install /dev/hda (or /dev/sda)
- Can add stanzas to /boot/grub/grub/conf for other operating systems including the original pre-clone system, MS Windows, Ubuntu, FreeBSD, ...
Migration from RHEL5 to CentOS5
"All that you should need to do is install centos-release, remove redhat-release rpms and just yum update the machine, which should bring in all packages changed by CentOS ( since they will have a slightly higher E-V-R )." - per KaranbirSingh on centos-list
- You may also wish to remove the "rhnplugin" from yum (not necessary but gives an error msg)
OR - per Craig White on centos-list Mon, 29 Oct 2007...
# cp /etc/redhat-release /etc/redhat-release-saved # rpm -e --nodeps redhat-release-notes redhat-release yum-rhn-plugin redhat-logos # rpm -ivh \ http://mirror.centos.org/centos/5/os/i386/CentOS/centos-release-5-0.0.el5.centos.2.i386.rpm \ http://mirror.centos.org/centos/5/os/i386/CentOS/centos-release-notes-5.0.0-2.i386.rpm # yum update
Note: It is only possible to pull the lastest 'point release' packages directory from the host: mirror.centos.org Older point release packages are relocated to: vault.centos.org and so for the foregoing example, we would use:
# cp /etc/redhat-release /etc/redhat-release-saved # rpm -e --nodeps redhat-release-notes redhat-release yum-rhn-plugin redhat-logos # rpm -ivh \ http://vault.centos.org/5.0/os/i386/CentOS/centos-release-5-0.0.el5.centos.2.i386.rpm \ http://vault.centos.org/5.0/os/i386/CentOS/centos-release-notes-5.0.0-2.i386.rpm
See also
