Chapter 44. Manually Upgrading the Kernel

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The Red Hat Enterprise Linux kernel is custom built by the Red Hat Enterprise Linux kernel team to ensure its integrity and compatibility with supported hardware. Before Red Hat releases a kernel, it must first pass a rigorous set of quality assurance tests.
Red Hat Enterprise Linux kernels are packaged in RPM format so that they are easy to upgrade and verify using the Package Management Tool, or the yum command. The Package Management Tool automatically queries the Red Hat Enterprise Linux servers and determines which packages need to be updated on your machine, including the kernel. This chapter is only useful for those individuals that require manual updating of kernel packages, without using the yum command.


Building a custom kernel is not supported by the Red Hat Global Services Support team, and therefore is not explored in this manual.


The use of yum is highly recommended by Red Hat for installing upgraded kernels.
For more information on Red Hat Network, the Package Management Tool, and yum, refer to Chapter 15, Registering a System and Managing Subscriptions.

44.1. Overview of Kernel Packages

Red Hat Enterprise Linux contains the following kernel packages (some may not apply to your architecture):
  • kernel — Contains the kernel for multi-processor systems. For x86 system, only the first 4GB of RAM is used. As such, x86 systems with over 4GB of RAM should use the kernel-PAE.
  • kernel-devel — Contains the kernel headers and makefiles sufficient to build modules against the kernel package.
  • kernel-PAE (only for i686 systems) — This package offers the following key configuration option (in addition to the options already enabled for the kernel package):
    • PAE (Physical Address Extension) support for systems with more than 4GB of RAM, and reliably up to 16GB.


      Physical Address Extension allows x86 processors to address up to 64GB of physical RAM, but due to differences between the Red Hat Enterprise Linux 4 and 5 kernels, only Red Hat Enterprise Linux 4 (with the kernel-hugemem package) is able to reliably address all 64GB of memory. Additionally, the Red Hat Enterprise Linux 5 PAE variant does not allow 4GB of addressable memory per-process like the Red Hat Enterprise Linux 4 kernel-hugemem variant does. However, the x86_64 kernel does not suffer from any of these limitations, and is the suggested Red Hat Enterprise Linux 5 architecture to use with large-memory systems.
  • kernel-PAE-devel — Contains the kernel headers and makefiles required to build modules against the kernel-PAE package.
  • kernel-doc — Contains documentation files from the kernel source. Various portions of the Linux kernel and the device drivers shipped with it are documented in these files. Installation of this package provides a reference to the options that can be passed to Linux kernel modules at load time.
    By default, these files are placed in the /usr/share/doc/kernel-doc-<version>/ directory.
  • kernel-headers — Includes the C header files that specify the interface between the Linux kernel and userspace libraries and programs. The header files define structures and constants that are needed for building most standard programs.
  • kernel-xen — Includes a version of the Linux kernel which is needed to run Virtualization.
  • kernel-xen-devel — Contains the kernel headers and makefiles required to build modules against the kernel-xen package


The kernel-source package has been removed and replaced with an RPM that can only be retrieved from Red Hat Network. This *.src.rpm package must then be rebuilt locally using the rpmbuild command. For more information on obtaining and installing the kernel source package, refer to the latest updated Release Notes (including all updates) at
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