How do I install FreeBSD kernel source code?

To install the FreeBSD kernel source code on a FreeBSD system, you will need to do the following:

1. Update the system's package database by running the following command:

# pkg update

2. Install the FreeBSD kernel source code package using the pkg package manager:

# pkg install kernel-sources

This will install the FreeBSD kernel source code in the /usr/src directory.

Alternatively, you can also download and extract the FreeBSD kernel source code tarball from the FreeBSD website and extract it to the /usr/src directory.

For example, to download and extract the FreeBSD 12.2 kernel source code tarball, you can use the following commands:

# cd /usr/src
# fetch https://download.freebsd.org/ftp/releases/amd64/12.2-RELEASE/src.txz
# tar -xf src.txz

This will download and extract the kernel source code tarball to the /usr/src directory.

Once the kernel source code is installed, you can build and install a custom kernel by following the instructions in the FreeBSD Handbook or the buildkernel man page.

For more information about installing and using the FreeBSD kernel source code, you can refer to the FreeBSD Handbook and the buildkernel man page by running man buildkernel on the command line.