How to Build a Custom Live CD with `mfsBSD` on FreeBSD

Introduction

Creating a custom Live CD for FreeBSD is useful for system recovery, network booting, and portable FreeBSD environments. One of the simplest and most effective ways to create a FreeBSD Live CD is by using mfsBSD. This lightweight and versatile tool allows users to build minimal FreeBSD images that can be booted from CD, USB, or over the network.

In this guide, we will cover the step-by-step process of building a custom Live CD with mfsBSD on the FreeBSD operating system.

Prerequisites

Before proceeding, ensure you have the following:

1. A FreeBSD system (or virtual machine) with root access.
2. A working internet connection.
3. Basic familiarity with the FreeBSD command line.
4. git, make, and xz installed on your FreeBSD system.

If these tools are not installed, you can install them using:

pkg install git gmake xz

Step 1: Download and Install mfsBSD

mfsBSD is an open-source project available on GitHub. To download and install it, run:

git clone https://github.com/mmatuska/mfsbsd.git
cd mfsbsd

This will create a directory named mfsbsd, containing the necessary scripts and configurations for building the Live CD.

Step 2: Configure mfsBSD

Inside the mfsbsd directory, you will find a file named settings.sh. This file contains various options for customizing the Live CD. Open it with a text editor:

vi settings.sh

Modify the following parameters based on your needs:

• MFSROOT_MAXSIZE: The maximum size of the RAM disk.
• MFSROOT_TYPE: Set to md for memory disk or ufs for UFS.
• CUSTOM_KERNCONF: Specify a custom kernel configuration if needed.
• WORLD_FLAGS: Additional flags for FreeBSD world build.

For a minimal image, you can leave most settings as default.

Step 3: Build the Base System

Now, build the FreeBSD world and kernel for the Live CD:

make buildworld
make buildkernel

If you need a custom kernel, modify the KERNCONF parameter accordingly.

Once the build process is complete, install the system into a temporary directory:

make installworld DESTDIR=`pwd`/work
make installkernel DESTDIR=`pwd`/work
make distribution DESTDIR=`pwd`/work

The work/ directory will now contain the necessary FreeBSD binaries and libraries.

Step 4: Configure System Settings

To make your Live CD functional, configure essential system files within the work/ directory.

Set Up /etc/rc.conf

Create or modify the rc.conf file:

echo 'hostname="mfsbsd"' > work/etc/rc.conf
echo 'ifconfig_DEFAULT="DHCP"' >> work/etc/rc.conf

Enable SSH

If you want SSH access, enable the SSH daemon:

echo 'sshd_enable="YES"' >> work/etc/rc.conf
echo 'PermitRootLogin yes' >> work/etc/ssh/sshd_config

Add a Default Root Password

To set a default password for the root user:

echo 'root::0:0::0:0:Charlie &:/root:/bin/sh' > work/etc/master.passwd
pwd_mkdb -d work/etc work/etc/master.passwd

This will allow login without a password, useful for recovery purposes.

Step 5: Build the mfsBSD Image

Now, generate the compressed RAM disk:

make mfsroot

This will create a mfsroot.gz file that contains the minimal FreeBSD system.

Step 6: Create the ISO Image

To build the final ISO image, run:

make iso

The output will be an ISO file in the mfsbsd/ directory, which you can burn to a CD or write to a USB drive.

Step 7: Test the Live CD

Before deploying, test the Live CD using QEMU:

qemu-system-x86_64 -cdrom mfsbsd.iso -m 512

Alternatively, if you want to test it on a physical machine, burn the ISO to a CD or write it to a USB stick using dd:

dd if=mfsbsd.iso of=/dev/da0 bs=1M

Replace /dev/da0 with the actual USB device identifier.

Customizations

Adding Additional Packages

To include additional packages, chroot into the work/ directory and install them:

chroot work
pkg install nano htop
exit

Then rebuild the image using:

make mfsroot
make iso

Customizing the Kernel

If you need custom kernel options, create a new kernel configuration file in /usr/src/sys/amd64/conf/ (or the appropriate architecture directory), then modify settings.sh to use it.

Conclusion

Using mfsBSD, you can build a custom FreeBSD Live CD tailored to your needs. Whether for recovery, network booting, or portable FreeBSD environments, this method provides flexibility and ease of customization. By following these steps, you can create a lightweight and functional FreeBSD-based Live CD, ready for deployment.