II want to dual boot my Windows with a Linux system. You ask why? It looks much more fun and exploratory. This is not an article on why I am changing in detail or my journey to this decision. This is just a documentation on the process to dual boot with my existing Windows. yes, i know, I would still need Windows. it has a way of pulling you back in for one thing or the other.
I picked Catchy OS. This is a variant of Arch Linux. I have tried it on an exernal hard drive and I believe I can cope now. Why Cachy. Well, they say it caches so it's faster. I partly agree but realized they played a trick on us. The kernel is not complete. I could even use ip-tabes in the default kernel. I guess that won't be a need for many users. Switching Kernels is not so difficult. That is part of the learning process. You have a system you can tinker and learn from.
The instruction below guides on the dual boot installation. Dissapointment alert. I generated this from ChatGPT. Hopefully no hallucinations and dangerous assumptions.
You want to dual-boot CachyOS with Windows on your NVMe internal drive, so I’ll cover:
🧭 Preparation inside Windows
💽 Bootable USB creation
⚙️ BIOS / Boot setup
🪟 Safe partitioning
💡 Installation details (CachyOS installer)
🔄 GRUB + EFI handling
⚠️ Reversal / recovery (if you change your mind)
🧭 1️⃣ Prepare Windows
✅ Back up first
Back up your important files to cloud or external disk. We won’t touch Windows, but mistakes happen.
✅ Disable “Fast Startup”
Prevents NTFS locks that confuse Linux:
Control Panel → Power Options → Choose what the power buttons do → Change settings that are currently unavailable → Uncheck “Turn on fast startup” → Save.
✅ Disable BitLocker (if enabled)
If your drive is encrypted, suspend or disable BitLocker before partitioning.
✅ Shrink your Windows partition
Right-click Start → Disk Management
Right-click your main C: drive → Shrink Volume
Leave unallocated space (recommended below 👇)
💽 2️⃣ Create CachyOS USB
🧰 You’ll need:
CachyOS ISO → download from https://cachyos.org/download/
Rufus on Windows
⚙️ Rufus Settings:
Device → your USB
Boot selection → CachyOS ISO
Partition scheme → GPT
Target system → UEFI (non-CSM)
Click Start
⚙️ 3️⃣ BIOS Settings (before boot)
Reboot → press F1 / F2 / F10 / F12 (depends on Lenovo) to enter BIOS.
Ensure:
UEFI mode is enabled (not Legacy/CSM)
Secure Boot → disabled
Boot order: USB first
💾 4️⃣ Recommended Partition Sizes
Partition Mount point Type Size Notes
EFI (existing) /boot/efi FAT32 Already exists (~100–500 MB) Do not delete — just use it
Root / ext4 or btrfs 80–100 GB OS, apps, updates
Home /home ext4 or btrfs 100–150 GB User data
Swap swap optional 4–8 GB For suspend/hibernate
➡️ Total suggestion: 200–250 GB for CachyOS, leaving plenty for updates, packages, etc.
If you have a 1 TB NVMe, that’s ~25% to Linux, 75% to Windows — ideal.
🧩 5️⃣ Install CachyOS
Boot from the USB → choose “Boot CachyOS Installer.”
When asked about partitioning, choose “Install alongside Windows Boot Manager” if available.
If not, choose manual partitioning and use the unallocated space.
Select your existing EFI partition (usually /dev/nvme0n1p1) and set Mount point: /boot/efi but do not format it.
Proceed — CachyOS will install GRUB and detect Windows automatically.
When done, reboot → you’ll see GRUB menu with:
CachyOS
Windows Boot Manager
🪟 6️⃣ Post-install: Accessing Windows from Linux
Once booted into CachyOS:
sudo mkdir /mnt/windows
sudo lsblk
Find your Windows partition (often /dev/nvme0n1p3), then mount:
sudo mount /dev/nvme0n1p3 /mnt/windows
You can browse it in your file manager and optionally make it auto-mount in /etc/fstab.
⚠️ 7️⃣ If You Change Your Mind Later
You can reverse or remove CachyOS safely:
Boot into Windows.
Open Command Prompt (Admin) and run:
bcdedit /set {bootmgr} path \EFI\Microsoft\Boot\bootmgfw.efi
This restores Windows boot as default.
Delete the Linux partitions from Disk Management (right-click → Delete Volume).
Optionally expand your Windows partition to reclaim the freed space.
To remove GRUB entry, you can also run:
bcdboot C:\Windows
(or use EasyUEFI GUI tool)
💡 The EFI entries are stored separately; removing GRUB or changing default boot doesn’t break Windows.
🧠 8️⃣ Common Warnings
❗ Never format or delete the EFI partition. Just reuse it.
❗ Always install CachyOS in UEFI mode, same as Windows (both GPT).
❗ Turn off Fast Startup & Hibernation in Windows — otherwise Linux mounts Windows read-only.
✅ Keep a Windows USB handy in case you ever need to repair boot.