Different kernel flavors (UP, SMP, ENTERPRISE, ENTNOSPLIT)

OpenVZ project releases several different precompiled kernels for each version. Which kernel to choose depends on what hardware you have. The table below describes the cases when it is better to use each of these kernels.

RHEL6-based kernels

RHEL6 kernels come in single flavor only which is SMP and PAE (for 32bit) enabled. This is because nowadays it's hard to find machines with single core CPUs and less than 4GB RAM.

Note: RHEL6 kernels no longer support enterprise versions of 32bit kernels with 4/4GB split, which limits 32bit version.

RHEL5-based kernels

i686 kernel flavors list

Kernel type	Description	Hardware	Use case
i686 UP	uniprocessor	up to 4GB of RAM
i686 SMP	symmetric multiprocessor	up to 4 GB of RAM	10-20 Containers
i686 entnosplit/PAE	SMP + PAE support	up to 64 GB of RAM	10-30 Containers
i686 enterprise/ent	SMP + PAE support + 4/4GB split	up to 64 GB of RAM	>20 Containers

These kernels are optimized for these types of hardware configurations and usage scenarios, so choosing the right kernel can help to boost performance by about 5 to 15 per cent.

Note: Use rpm -ihv command for ovzkernel RPM installation. Please do not use the rpm -Uhv command to install the kernel, otherwise all the previously installed kernels may be removed from your system.

Note: When using a 64-bit processor and operating system, you need only select the SMP or non-SMP version. With the Redhat repos this will be ovzkernel.x86_64. 64-bit linux can access the entire RAM in ZONE_NORMAL (low memory). PAE and 4GB/4GB splitting is only needed for 32-bit OS, and so are not necessary and are disabled by default in 64-bit kernels.

New RHEL5 based kernel uses different flavors naming:

• UP kernel is no longer provided
• SMP kernel comes without any flavor (like old UP)
• entnosplit kernel comes as PAE
• enterprise kernel comes as ent
• ovzkernel.x86_64 for 64-bit