8.5. Building and Installing a Custom Kernel
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## 8.5. Building and Installing a Custom Kernel

Once the edits to the custom configuration file have been saved, the source code for the kernel can be compiled using the following steps:

Procedure 8.1. Building a Kernel

1. Change to this directory:

       # cd /usr/src

2. Compile the new kernel by specifying the name of the custom kernel configuration file:

       # make buildkernel KERNCONF=MYKERNEL

3. Install the new kernel associated with the specified kernel configuration file. This command will copy the new kernel to `/boot/kernel/kernel` and save the old kernel to `/boot/kernel.old/kernel`:

       # make installkernel KERNCONF=MYKERNEL

4. Shutdown the system and reboot into the new kernel. If something goes wrong, refer to The kernel does not boot.

By default, when a custom kernel is compiled, all kernel modules are rebuilt. To update a kernel faster or to build only custom modules, edit `/etc/make.conf` before starting to build the kernel.

For example, this variable specifies the list of modules to build instead of using the default of building all modules:

    MODULES_OVERRIDE = linux acpi

Alternately, this variable lists which modules to exclude from the build process:

    WITHOUT_MODULES = linux acpi sound

Additional variables are available. Refer to make.conf(5) for details.

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