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Triple Boot Setup: Windows 10, Linux Mint 21.3 XFCE, and OpenBSD 7.8

This is a step-by-step guide to set up a triple-boot system with Windows 10, Linux Mint 21.3 XFCE, and OpenBSD 7.8 on a Lenovo IdeaPad Flex 10 (Intel Celeron N2807, 2 GB RAM, 480 GB Kingston SSD).

Part One: Windows 10 Installation

1. Back up all important data — we will erase existing partitions and create new ones.

2. Insert the Windows 10 USB installer. Power on the laptop and press F2 repeatedly to enter BIOS setup (or Fn+F2).
- Disable Secure Boot.
- Set Boot Mode to UEFI (ensure Legacy/CSM is disabled).
- Set the USB as the first boot device (or use the one-time boot menu — often Fn+F12).
- Save changes (usually F10) and exit.

3. Boot from the Windows USB. Choose Custom: Install Windows only (advanced).
- Delete all existing partitions until only "Unallocated Space" remains.
- Create a new partition of ~128 GB (Windows will auto-create the small EFI System Partition ~100–500 MB).
- Select the new 128 GB partition and click Next to install.

4. After the first reboot, remove the Windows USB.
Complete setup: create a local user account (skip Microsoft account/Wi-Fi if possible).

Part Two: Linux Mint 21.3 XFCE Installation

1. Insert the Linux Mint USB. Boot into BIOS (F2) and select the USB to boot (or use Fn+F12 boot menu).

2. From the live desktop, click the Install Linux Mint icon.
Proceed through the setup until you reach the partitioning step.
Choose Something else (manual partitioning).

3. In the partition editor:
- Select the free space after the Windows partitions.
- Create a new ~128 GB partition: filesystem ext4, mount point / (root).
- Do not format the existing small FAT32 EFI partition (~100–500 MB, usually first on disk, flagged "boot, esp").
- Write changes and continue.

4. Finish the installation and reboot. Remove the Linux Mint USB.

Part Three: Boot Linux Mint and Prepare Disk for OpenBSD

1. Boot into Linux Mint, connect to Wi-Fi.
Open Update Manager (shield icon in tray or menu).
Switch to a local/fast mirror if desired, then refresh. You can apply updates now or later.

2. Open DISKS UTILITY from the menu.
In the remaining free space:
• Create a ~128–150 GB partition (leave as unformatted / other — OpenBSD installer will handle it).
• Create a ~90 GB partition: filesystem FAT32 (shared storage accessible from all OSes).

3. Open a terminal and check partitions:
sudo fdisk -l
Note the device (likely /dev/sda) and partition numbers (e.g., sda6 = OpenBSD area, sda7 = shared FAT32).

4. (Usually optional — skip unless needed) Set OpenBSD partition type:
sudo fdisk /dev/sda
→ t (change type)
→ Enter partition number (e.g., 6 for OpenBSD area)
→ Type 104
→ p to print and verify
→ w to write changes.

5. Reboot and proceed to OpenBSD installation.

Part Four: OpenBSD 7.8 Installation

1. Insert the OpenBSD USB. Enter BIOS (F2) and boot from the USB.

2. At the boot prompt, type I to start the installer.

3. Select keyboard layout (default usually works).

4. Set system hostname (e.g., openbsdbox).

5. Network setup: select the correct interface (likely em0 or similar), choose auto/DHCP configuration.

6. Set root password.

7. Start sshd? yes (recommended).

8. Start the X Window System? no (low RAM — stay console or add lightweight WM later).

9. Create a regular user account.

10. Select disk: sd0.

11. Use (W)hole disk or (O)penBSD area? → Choose O and select the partition you prepared for OpenBSD (do not choose W!).

12. Use (A)uto layout? → yes (or customize if preferred).

13. Install from HTTP: server cdn.openbsd.org, path /pub/OpenBSD/7.8/amd64/ (or closer mirror).

14. Select sets: choose all (or minimal if concerned about RAM).

15. Set time zone (e.g., America/Halifax).

16. Finish installation and reboot. Remove the USB.

Part Five: Install rEFInd Boot Loader

1. Boot into Linux Mint (GRUB should still work initially).

2. Open a terminal and run:

sudo add-apt-repository ppa:rodsmith/refind
sudo apt update
sudo apt install refind

When prompted "Install rEFInd to the ESP?" select Yes.

3. Reboot.

4. If rEFInd does not appear automatically:
Enter BIOS (F2) → Boot menu → look for "rEFInd Boot Manager" (or sometimes labeled "ubuntu") and move it to the top or select it.

5. rEFInd should now display entries for Windows, Linux Mint, and OpenBSD.
Test booting into each operating system.

Good luck! This setup is ambitious on only 2 GB RAM, but it works with lightweight usage.