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Forest OS - Frequently Asked Questions

Here you'll find answers to the most common questions about this unix-like operating system.

1. What is Forest OS?

Forest OS (codename ALDER) is a unix-like, POSIX-oriented operating system built from scratch. It consists of three main components:

• Fern — the kernel
• foreboots (ForeB) — the bootloader (BIOS and UEFI)
• libc — a POSIX-oriented C standard library

Forest OS is deliberately kernel-oriented: it focuses on providing a solid foundation rather than bundling a graphical desktop or a full userspace application suite. You build it, boot it, and customize it for your needs.

2. Is it a Linux distribution?

No. Forest OS is not a Linux distribution. It is an independent operating system with its own kernel (Fern), its own bootloader (foreboots), and its own C library. While it aims for POSIX compatibility and uses Linux-compatible system call numbers, it is entirely separate from the Linux kernel and Linux-based systems.

3. Why build a custom OS?

People build custom operating systems for many reasons:

• Learning: Understanding how an OS works from the ground up is invaluable for systems programming
• Control: Having full control over every component, from bootloader to userspace
• Experimentation: Testing new ideas in OS design without the constraints of existing systems
• Education: Teaching operating system concepts in a practical, hands-on way
• Fun: There's something deeply satisfying about booting code you wrote yourself

Forest OS provides a clean, well-documented starting point for anyone interested in OS development.

4. What hardware does it run on?

Forest OS currently supports x86 architecture:

• 32-bit x86 (i686) — BIOS boot
• 64-bit x86_64 — BIOS and UEFI boot

The UEFI path also compiles for AArch64 (ARM64) and RISC-V 64, though x86 remains the primary development target.

For real hardware, any x86 PC with BIOS or UEFI firmware should work. In practice, testing in QEMU is recommended first.

5. How do I build it?

Prerequisites

On Debian/Ubuntu:

# For the cross-toolchain
sudo apt install build-essential gcc g++ make flex bison gawk \
                 texinfo curl wget tar xz-utils \
                 libgmp-dev libmpfr-dev libmpc-dev

# For Fern + foreboots + images
sudo apt install nasm clang lld xorriso mtools python3 \
                 qemu-system-x86 ovmf dialog

Build Steps

# 1. Clone the repo
git clone https://github.com/Enclica-Forest/Forest forest
cd forest

# 2. Set the forest root
export FOREST="$(pwd)"

# 3. Build the cross-toolchain
cd forestos-toolchain
./build-toolchain.sh --arch both
cd ..

# 4. Configure Fern
cd fern
./conf.sh --defconfig

# 5. Build the kernel
make build

# 6. Build userspace apps
cd ../userspace
make

# 7. Copy apps into initrd
cp build/bin/* ../fern/initrd/bin/
ln -sf forest-shell ../fern/initrd/bin/shell
ln -sf forest-shell ../fern/initrd/bin/sh

# 8. Rebuild kernel with updated initrd
cd ../fern
make build

# 9. Build bootable image
make forebo-image

# 10. Run it!
make run

6. How do I run it in QEMU?

After building, use these commands from the fern/ directory:

# Run with default settings (honors configured BOOT_MODE)
make run

# Force BIOS boot
make run-bios

# Force UEFI boot
make run-uefi

# 32-bit BIOS
make run32

# 64-bit BIOS
make run64

# Debug mode (GDB stub on :1234)
make debug

You can also use the createos.sh script for a guided, menu-driven build experience:

cd $FOREST
./createos.sh

7. How do I install it on real hardware?

Warning: This will destroy existing data on the target device!

For BIOS systems:

# Write the raw disk image to a USB drive or HDD
sudo dd if=$FOREST/foreboots/build/forebo.img of=/dev/sdX bs=1M conv=fsync
sync

For UEFI systems:

Write esp.img to a FAT partition, or use the hybrid forebo.iso on removable media.

Always double-check the device node before writing. The forebo.img file contains the bootloader stages and the Fern kernel embedded together.

8. What filesystems are supported?

Forest OS supports:

• FAT — via the UEFI firmware for the EFI System Partition
• ext2/3/4 — read-only support in the UEFI shell and recovery tools
• btrfs — detection and subvolume/snapshot listing (read-only, best-effort)
• devtmpfs — kernel-created device filesystem
• procfs — process information filesystem
• sysfs — kernel object filesystem
• tmpfs — temporary filesystem in RAM

The root filesystem is typically an initrd (tar archive) loaded at boot time.

9. Does it have networking?

Forest OS includes networking headers and system call wrappers in the libc (socket, bind, listen, accept, connect, send, recv), but networking support is still in development. The kernel provides the foundation, and full network stack implementation is an ongoing area of work.

10. Does it have a GUI?

Forest OS is deliberately kernel-oriented and does not bundle a graphical desktop. However:

• The bootloader (foreboots) has a graphical boot menu with a forest theme, mouse support, and windowed tools on UEFI
• The kernel supports framebuffer output
• You can build and add your own graphical applications using the framebuffer APIs

The focus is on providing a solid foundation that you can build upon.

11. Can I run Linux binaries?

Not directly. Forest OS uses its own ABI and system call interface, though it uses Linux-compatible system call numbers. Simple, statically-linked programs might work with recompilation, but:

• Programs must be compiled with the Forest OS cross-toolchain (i686-forestos-gcc / x86_64-forestos-gcc)
• Dynamic linking requires the Forest OS libc and dynamic linker
• Complex Linux-specific programs will need porting

The goal is POSIX compatibility, not Linux binary compatibility.

12. How does it compare to other hobby OSes?

Forest OS stands out with its clean design, well-documented codebase, and focus on being a practical learning tool.

13. Is it production ready?

No. Forest OS is a hobby/educational operating system. It is not intended for production use. There are many areas that need work:

• Full POSIX compliance
• Network stack
• Device drivers
• Memory management optimizations
• Security hardening

It is, however, excellent for learning, experimenting, and as a foundation for your own OS projects.

14. How can I contribute?

Forest OS is an open project and contributions are welcome:

1. Read the documentation — Start with MAKE_AN_OS.md and the component READMEs
2. Try building it — Get it running in QEMU and explore
3. Pick an area — Kernel, bootloader, libc, userspace apps, documentation
4. Start small — Fix a bug, add a feature, improve documentation
5. Submit changes — Follow the existing code style and conventions

Areas that especially need help:

• Device drivers
• Network stack implementation
• More userspace applications
• Documentation improvements
• Testing on real hardware

15. What's the license?

Forest OS is licensed under the GNU General Public License v3 (GPLv3). This means:

• You can freely use, modify, and distribute the code
• Changes must be released under the same license
• Source code must be made available
• There is no warranty

Some vendored libraries (like uacpi) have their own licenses (MIT in uacpi's case).

16. Where can I find help?

• Documentation: Check the wiki/ directory for detailed guides
• Component READMEs: Each component has its own README with specific information
• fern/README.md — Kernel overview
• foreboots/README.md — Bootloader details
• libs/libc/README.md — C library documentation
• MAKE_AN_OS.md: The complete build guide from start to finish
• AGENTS.md: Build system reference (if present)
• Source code: The code is well-commented and designed to be read

For specific issues, check the troubleshooting section in MAKE_AN_OS.md for common problems and solutions.

Additional Resources

• Build Guide — Complete build instructions
• Kernel Documentation — Fern kernel details
• Bootloader Documentation — ForeB bootloader guide
• C Library Documentation — Forest OS libc reference

Last updated: August 2026