Dual boot
Install Cyclop OS next to Windows.
Keep Windows and add Cyclop OS on the same computer, and choose which one to start each time. The work is mostly in preparing Windows; the installation itself is short.
Before anything, back up
Resizing a disk is safe when it goes well and costs you everything when it does not (a power cut halfway through is enough). Copy the files you care about to an external disk before you start. Do it even if you are sure.
Suspend BitLocker, or decrypt
If Windows encrypts its disk with BitLocker (many recent laptops do it without telling you, under the name device encryption), changing the partitions can lock Windows at the next start and ask for a 48-digit recovery key.
Before you touch the disk, open Windows settings, search for BitLocker or device encryption, and either suspend protection or turn it off. Find your recovery key first, in your Microsoft account, in any case.
Turn off Fast Startup
Fast Startup makes Windows shut down halfway, leaving its disk in a state that no other system should write to. Installing next to it in that state is how Windows files end up damaged.
- Open Control Panel, then Power Options.
- Choose what the power buttons do, then Change settings that are currently unavailable.
- Untick Turn on fast startup, and save.
- Shut Windows down fully (Shut down, not Restart) before moving on.
Free some space
Cyclop OS needs 20 GB at the very least and 40 GB or more on an SSD to be comfortable. Add what you will keep on it. Leave Windows a generous margin too: a Windows disk filled to the brim becomes slow.
- In Windows, open Disk Management (right-click the Start button).
- Right-click your main Windows partition (usually C:) and choose Shrink Volume.
- Enter the space to free, in megabytes (40 GB is about 40000), and confirm.
- A block marked Unallocated appears. Leave it as it is: do not format it, and do not give it a letter.
If Windows offers to shrink by much less than you asked, immovable files sit at the end of the partition. Restart, run the disk clean-up, and try again.
Start the installer and choose how to install
Start the computer from the USB drive as in the installation guide, and follow the first screens up to the choice of how to install.
When the installer sees another operating system on the disk, it offers Install alongside, which shrinks a partition to make room. If you already freed space in Windows, you can also pick Manual partitioning and use the unallocated space.
Never choose Automatic Setup (Use entire disk): it erases everything on the disk, Windows included.
We have read this behaviour in the installer’s code and not yet followed it from start to finish on a real Windows machine. If a screen does not match this page, stop before the summary and ask on the forum.
Screenshot to provide: the installer step where the choices appear on a disk that already holds Windows (Install alongside, Automatic Setup, Manual partitioning).
If you partition by hand
Create the Cyclop OS partition in the unallocated space, formatted ext4 and mounted at /.
Reuse the EFI partition Windows already has (about 100 to 300 MB, FAT32) and mount it at /boot/efi. Do not format it: Windows starts from it.
Nothing is written until you confirm on the summary screen, which lists every operation. Read it, and check that the Windows partitions are not on the list of things to be formatted.
Choose at startup
After the installation, a menu at startup lets you pick between Cyclop OS and Windows. If it does not appear, hold Shift while the machine starts, or tap Escape.
If Windows is missing from that menu, the computer’s own boot menu still lists both. Its key depends on the brand (Escape, F2, F10, F12 are the usual ones). Once in Cyclop OS, the command below rebuilds the menu and looks for Windows again.
sudo update-grub
We have not yet verified on a real machine that the Windows entry appears by itself after the installation. This is the first thing to tell us if it does not.
Screenshot to provide: the boot menu at startup showing Cyclop OS and Windows side by side.
Two small things afterwards
The clock can be off by an hour or two in one of the two systems: Windows keeps the hardware clock in local time, Linux keeps it in universal time. If you see it, one command settles it from Cyclop OS: timedatectl set-local-rtc 1 --adjust-system-clock.
Windows updates sometimes put Windows first in the boot menu again. It only changes the order of the menu, nothing is lost.
With Secure Boot on, the Cyclop kernel needs its key enrolled once. The Secure Boot guide walks through it.