Hybrid Kernel

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Hybrid Kernel

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CloudLinux 5 Hybrid kernel


CL 5 Hybrid Kernel is CloudLinux 6 (2.6.32-lve1.x) kernel compiled for CloudLinux 5 OS. It brings new features available in CloudLinux 6 kernel, like IO limits, to CloudLinux 5 servers. When you switch to hybrid kernel, you will also switch to a new channel, that has all other components compatible with the new kernel. The kernel is as stable as the CloudLinux 6 production kernel and has same features.


While the kernel itself is fully production quality, the process of switching to hybrid kernel is not perfect. This is mostly due to differences in naming for the devices and modules between 2.6.32 and 2.6.18 kernels. As the result, your server might not boot with new kernel. To solution that, boot into previous (CL5) kernel, and convert back. After that -- notify our support department at https://helpdesk.cloudlinux.com. In most cases we can resolve all the naming issues, and make sure you can boot into hybrid kernel


Switching to Hybrid kernel:


# yum update rhn-setup
# /usr/sbin/normal-to-hybrid
# reboot


To convert back to original CloudLinux 5 kernel:


# yum update rhn-setup
# /usr/sbin/hybrid-to-normal
# reboot



CloudLinux 6 Hybrid kernel


CL 6 Hybrid Kernel is CloudLinux 7 (3.10.0) kernel compiled for CloudLinux 6 OS. New 3.10 kernel features a set of performance and scalability improvements related to IO, networking and memory management, available in CloudLinux 7 OS. It also features improved CPU scheduler for better overall system throughput and latency.


Please find information on the main features of 3.10 kernel branch on the links:






How to migrate from the normal to hybrid channel:


Note. The system must be registered in CLN.


1. Update rhn-client-tools from beta


2. Run normal-to-hybrid script.


3. Reboot after script execution is completed.


yum update rhn-client-tools --enablerepo=cloudlinux-updates-testing




How to migrate from hybrid to the normal channel:


Note. The system should be registered in CLN.


1. Run hybrid-to-normal script.


2. Reboot after script execution is completed.





Known limitations and issues:


1. We do not remove Hybrid kernel after migration from Hybrid to the normal channel, but we remove linux-firmware package which is needed to boot Hybrid kernel. This is because CL6 does not allow to remove the package of currently running kernel. Proper removal procedure will be implemented, but for now, we should warn users not to boot Hybrid kernel if they have migrated to normal channel.


2. Kernel module signature isn't checking for now, as 3.10 kernel is using x509 certificates to generate keys and CL6 cannot detect signatures created in such way. The solution will be implemented.