🔥Installing OPNsense on a pfSense SG-4860: Fixing the Console Output Problem

##Problem

I had a pfSense SG-4860 running a version of pfSense from 2017. I wanted to replace it with OPNsense, but when I booted the OPNsense installer via USB, I got no output on the serial console. The device was clearly booting—pulling power, drive activity—but the console was completely blank.

I tried different baud rates, different terminal emulators, different USB-to-serial adapters, various key sequences to interrupt the boot, and even asked Claude for help. Nothing worked.

After days of searching, I found a thread on the OPNsense forum↗ where a user named pylox had the same problem and solved it by editing the boot configuration files directly on the installer media.

##Solution

The OPNsense installer's default console speed doesn't match what the SG-4860 expects. Mount the installer USB drive and edit (or create) /boot/loader.conf.local:

comconsole_speed="115200"

That single line is all I needed. After this change, the installer booted with full console output and the installation proceeded normally.

###Mounting the FreeBSD Installer on macOS

The OPNsense installer uses a FreeBSD filesystem (UFS) which macOS can't read natively. Here's how to mount it:

1. Enable system extensions — If you haven't already, reboot into Recovery Mode and enable system extensions. This is a one-time setup required for third-party kernel/system extensions.

2. Install macFUSE and fuse-ufs2

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brew install --cask macfuse
brew install macos-fuse-t/homebrew-cask/fuse-ufs2

3. Grant permissions — Go to System Settings > Privacy & Security and approve the system extensions for both macFUSE and fuse-ufs2. Restart if prompted.

4. Mount the installer drive

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diskutil list

Find the USB drive (e.g. /dev/disk4) and locate the freebsd-ufs partition (usually s3 or similar).

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sudo fuse-ufs /dev/disk4s3 /mnt/opnsense -o rw

5. Edit the boot config

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sudo nano /mnt/opnsense/boot/loader.conf.local

Add comconsole_speed="115200", save, and unmount:

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sudo umount /mnt/opnsense

###If That's Not Enough

pylox's forum post↗ suggested a larger set of changes. I only needed comconsole_speed, but if that alone doesn't work for your hardware, try the full set in /boot/loader.conf.local:

hint.uart.0.flags=0x0
hint.uart.1.flags=0x10
comconsole_speed="115200"
comconsole_port="0x2F8"
console="comconsole"
kern.cam.boot_delay="10000"

The comconsole_port changes which serial port is used, console forces serial console output, and kern.cam.boot_delay gives attached storage devices extra time to initialize.

##Credit

All credit goes to pylox on the OPNsense forum↗ for sharing this solution. I'm writing this because it took me days to find that thread, and I hope this saves the next person some time.