Red Hat Enterprise Linux 3: System Administration Guide
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# Chapter 39. Upgrading the Kernel

The Red Hat Enterprise Linux kernel is custom built by the Red Hat 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. For example, when the `kernel` RPM package distributed by Red Hat, Inc. is installed, an `initrd` image is created; thus, it is not necessary to use the `mkinitrd` command after installing a different kernel. It also modifies the boot loader configuration file to include the new kernel.

| Warning
| Building a custom kernel is not supported by the Red Hat Installation Support Team. For more information on building a custom kernel from the source code, refer to Appendix A Building a Custom Kernel.

# 39.1. Overview of Kernel Packages

Red Hat Enterprise Linux contains the following kernel packages (some may not apply to your architecture):

- `kernel` — contains the kernel and the following key features:

  - Uniprocessor support for x86 and Athlon systems (can be run on a multi-processor system, but only one processor is utilized)

  - Multi-processor support for all other architectures

  - For x86 systems, only the first 4 GB of RAM is used; use the `kernel-hugemem` package for x86 system with over 4 GB of RAM

- `kernel-hugemem` — (only for i686 systems) In addition to the options enabled for the `kernel` package. The key configuration options are as follows:

  - Support for more than 4 GB of RAM (up to 16 GB for x86)

  - PAE (Physical Address Extension), or 3 level paging on x86 processors that support PAE

  - Support for multiple processors

  - 4GB/4GB split — 4GB of virtual address space for kernel and almost 4GB for each user process on x86 systems

- `kernel-BOOT` — used during installation only.

- `kernel-pcmcia-cs` — contains support for PCMCIA cards.

- `kernel-smp` — contains the kernel for multi-processor systems. The following are the key features:

  - Multi-processor support

  - Support for more than 4 GB of RAM (up to 64 GB for x86)

  - PAE (Physical Address Extension), or 3 level paging on x86 processors that support PAE

- `kernel-source` — Contains the source code files for the Linux kernel

- `kernel-utils` — Contains utilities that can be used to control the kernel or system hardware.

- `kernel-unsupported` — exists for some architectures

  Because it is not possible for Red Hat Enterprise Linux to contain support for every piece of hardware available, this package contains modules that are not supported by Red Hat, Inc. during installation or after installation. The package is not installed during the installation process; it must be installed after installation. Drivers in the unsupported package are provided on a best-effort basis — updates and fixes may or may not be incorporated over time.

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