Source. My big thanks to author.
The following howto will show you how to migrate an Oracle Linux 6.7 OS instance to CentOS 6.7. In my tests I used a fully patched Oracle Linux 6.7 VM running Oracle Unbreakable Enterprise Kernel (UEK2) and the default package selection for Software Development Workstation.
The following howto will show you how to migrate an Oracle Linux 6.7 OS instance to CentOS 6.7. In my tests I used a fully patched Oracle Linux 6.7 VM running Oracle Unbreakable Enterprise Kernel (UEK2) and the default package selection for Software Development Workstation.
1. Update the OS, make sure kernel-uek is the default and reboot into runlevel 3
yum update sed -i 's/DEFAULTKERNEL=kernel/DEFAULTKERNEL=kernel-uek/' /etc/sysconfig/kernel sed -i 's/id:5/id:3/' /etc/inittab init 6
After reboot login as root and run the following commands:
2. Remove Oracle logos, release notes and other RPMs that may cause dependency issues later in the process (those will be automatically reinstalled)
rpm -e --nodeps `rpm -qa | grep rhn` oracle-logos oraclelinux-release \
oraclelinux-release-notes redhat-indexhtml dmidecode kpartx netxen-firmware \
redhat-release-server
3. Import the CentOS GPG keys
rpm --import http://mirror.centos.org/centos/6.7/os/x86_64/RPM-GPG-KEY-CentOS-6 rpm --import http://mirror.centos.org/centos/6.7/os/x86_64/RPM-GPG-KEY-CentOS-Debug-6
4. Install CentOS release files that include repository configuration
rpm -Uvh http://mirror.centos.org/centos/6.7/os/x86_64/Packages/centos-release-6-7.el6.centos.12.3.x86_64.rpm
At this stage the OS info has already
changed (/etc/redhat-release has been updated with CentOS version and
the yum repositories point to CentOS URLs) but we first need to update
yum before we go on.
5. Installing new yum
cd /root wget http://mirror.centos.org/centos/6.7/os/x86_64/Packages/yum-3.2.29-69.el6.centos.noarch.rpm wget http://mirror.centos.org/centos/6.7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.30-30.el6.noarch.rpm
The yum package has one dependency yum-plugin-fastestmirror so we need to install that first.
yum --disablerepo=* localinstall yum-plugin-fastestmirror-1.1.30-30.el6.noarch.rpm
Now we can install the new yum. Note
that we don’t actually update the already installed package, instead we
are downgrading it. We do that because the Oracle Linux yum RPM has an
additional suffix added to its %{RELEASE} tag which makes it higher in
version than the CentOS package which means we cannot update the former
with the latter, but we are allowed to downgrade. As you will see
below, there are more packages with the modified RELEASE tag in Oracle
Linux 6.
yum --disablerepo=* downgrade yum-3.2.29-69.el6.centos.noarch.rpm
Now the Oracle yum RPM has been replaced
by the CentOS package so after cleaning up the old cache we should be
able to access the new repositories.
yum clean all
yum repolist
6. Downgrade packages with changed suffix
As said above there are more packages
with modified RELEASE tags. I identified 130 RPMs which have different
tags compared to the CentOS version. The two possible additional tag
suffixes are 0.1 or 0.2. We’re going to query all RPMs and downgrade
them together with a few more RPMs that I found to be causing dependency
issues (again, those will be automatically reinstalled later in the
migration process).
rpm -qa | egrep "\.0\.(1|2)\.el6" >> to_downgrade cat to_downgrade | while read package; do rpm -q $package --qf '%{NAME}\n' >> dgrlist; done yum downgrade `cat dgrlist` dbus-glib-devel.x86_64 dbus-glib.x86_64 kexec-tools
7. Reinstall remaining Oracle packages
A complete migration means we get rid of
all Oracle packages and replace them with their corresponding CentOS
version. To do that we’ll use yum‘s reinstall function.
Basically an installed package can be reinstalled if the same version is
found in the available repositories. We’re using this yum feature to
identify all packages by Vendor (Oracle America) and have them replaced
with the same package versions from the CentOS repository.
rpm -qa --qf '%{NAME}:%{VENDOR}\n' | grep Oracle >> oraclepacks cat oraclepacks | awk -F":" '{print $1}' >> oraclepacks2 yum reinstall `cat oraclepacks2`
On my machine there were 1350 packages to reinstall. This can take some time as yum needs to download all packages.
8. Update the OS
After all packages have been either
downgraded or reinstalled we need to perform a full OS update to ensure
there were no leftovers in the migration process and we run the latest
RPMs available in the CentOS repositories.
yum update
9. Reboot to CentOS kernel
At this point the only remaining Oracle
RPMs should be the kernel-uek packages. Those were not processed since
we were running kernel-uek. We need to boot into a newly-installed
CentOS kernel and then we’ll be able to remove kernel-uek.
- sed -i 's/DEFAULTKERNEL=kernel-uek/DEFAULTKERNEL=kernel/' /etc/sysconfig/kernel
- modify /etc/grub.conf and set a new default CentOS kernel
-
init 6
10. Finally we can remove kernel-uek and install new kernel headers
rpm -e --nodeps `rpm -qa | grep kernel-uek` yum install kernel-headers
We can perform a final check to ensure there are no problems with the installed packages:
yum check
That’s it, the migration is complete. Hope this helps.
