How to Enable Linux Binary Compatibility (Linuxulator) on FreeBSD Operating System

FreeBSD is a powerful and flexible operating system that supports running native FreeBSD applications as well as software designed for other UNIX-like systems. One of its most useful features is Linux binary compatibility, often referred to as “Linuxulator.” This feature allows FreeBSD to run Linux programs, including proprietary applications that may not be natively available for FreeBSD.

Enabling Linuxulator on FreeBSD requires configuring the kernel, setting up the necessary libraries, and installing a compatible Linux userland. This guide will walk you through the steps needed to enable and configure Linux binary compatibility on FreeBSD.

1. Understanding Linux Binary Compatibility in FreeBSD

The Linux binary compatibility layer in FreeBSD works by intercepting system calls made by Linux applications and translating them into FreeBSD equivalents. This enables Linux applications to run without modification. However, the compatibility layer does not emulate the Linux kernel but instead provides an environment that mimics Linux system calls, libraries, and files.

FreeBSD includes support for running Linux binaries as a kernel module, which can be loaded dynamically when needed. Additionally, FreeBSD provides Linux distributions like CentOS and Debian as userland environments that complement this compatibility layer.

2. Checking FreeBSD Version and Kernel Compatibility

Before enabling Linuxulator, ensure that your FreeBSD system is compatible:

freebsd-version
uname -r

Ensure you are running FreeBSD 12.x, 13.x, or a later version, as they provide better support for Linux binary compatibility.

3. Enabling the Linux Kernel Module

To enable Linux binary compatibility, load the required kernel module:

sudo kldload linux
sudo kldload linux64

To make these changes persistent across reboots, add the following lines to /etc/rc.conf:

linux_enable="YES"

And to /boot/loader.conf:

linux_load="YES"
linux64_load="YES"

Verify that the modules are loaded:

kldstat | grep linux

If both linux.ko and linux64.ko appear in the output, the modules are successfully loaded.

4. Installing the Linux Base System

FreeBSD provides a Linux userland environment that allows Linux applications to function correctly. The linux_base package contains essential Linux libraries and binaries.

To install a Linux base system (CentOS 7 is commonly used):

sudo pkg install linux_base-c7

Once installed, enable the Linux environment:

sudo sysrc linux_enable="YES"
sudo service linux start

To check if Linux compatibility is enabled:

sysctl compat.linux.osrelease

This should return a Linux kernel version, such as 3.10.0 (CentOS 7). If not, set it manually:

sudo sysctl compat.linux.osrelease=3.10.0

To make this persistent across reboots, add the following to /etc/sysctl.conf:

compat.linux.osrelease=3.10.0

5. Configuring Linux File System Support

Some Linux applications require specific file system structures to function properly. FreeBSD provides /compat/linux/ as the root directory for the Linux userland.

Ensure that necessary directories exist:

sudo mkdir -p /compat/linux/proc
sudo mkdir -p /compat/linux/sys
sudo mkdir -p /compat/linux/dev

Mount the required file systems:

sudo mount -t linprocfs linproc /compat/linux/proc
sudo mount -t linsysfs linsys /compat/linux/sys
sudo mount -t devfs devfs /compat/linux/dev

To make these mounts persistent, add the following lines to /etc/fstab:

linproc   /compat/linux/proc  linprocfs rw  0  0
linsys    /compat/linux/sys   linsysfs  rw  0  0
devfs     /compat/linux/dev   devfs     rw  0  0

6. Running Linux Applications on FreeBSD

Once Linux binary compatibility is set up, you can run Linux applications. Test by running a basic Linux binary, such as the ls command from the Linux base package:

/compat/linux/bin/ls -l /

If you need to install additional Linux applications, use the FreeBSD package manager or manually install RPM-based software using tools like dnf (for CentOS-based environments).

For example, to install bash in the Linux environment:

sudo pkg install linux-c7-bash

Launch the Linux version of Bash:

/compat/linux/bin/bash

7. Installing and Running Steam or Proprietary Linux Software

If you want to run Linux-based proprietary software like Steam, you may need additional libraries and 32-bit compatibility:

sudo pkg install linux-steam-utils

For NVIDIA users, install the Linux graphics drivers:

sudo pkg install linux-nvidia-libs

Some applications might require pulseaudio for sound:

sudo pkg install linux-c7-pulseaudio

Run Steam using:

linux-steam

8. Troubleshooting Linux Binary Compatibility

If a Linux application fails to run, check for missing libraries:

ldd /compat/linux/bin/bash

If missing dependencies appear, install the required packages.

Check kernel logs for errors:

dmesg | grep linux

If an application does not work, try using an alternative Linux base system like linux_base-debian:

sudo pkg install linux_base-debian

To remove Linux compatibility, disable it and remove the installed components:

sudo sysrc linux_enable="NO"
sudo service linux stop
sudo pkg delete linux_base-c7

Conclusion

Enabling Linux binary compatibility (Linuxulator) on FreeBSD allows users to run Linux applications seamlessly. By loading the necessary kernel modules, installing a Linux base system, and configuring the environment, FreeBSD users can expand their software options significantly. Whether running simple command-line utilities or complex GUI applications like Steam, Linuxulator makes FreeBSD a versatile and powerful operating system for diverse use cases.