Dual-Booting AcreetionOS with Windows

Entirely reasonable. Do these five things and coexistence is boring (the good kind).

1. Make room BEFORE installing

Shrink Windows from within Windows (Disk Management → Shrink Volume). Leave ≥40 GB unallocated for AcreetionOS, then shut down fully.

2. Windows-side gotchas

Disable Fast Startup (Control Panel → Power Options → Choose what power buttons do). Fast Startup = permanent hibernation = NTFS always "in use" = Linux can’t safely mount it.
If BitLocker is on, suspend/recover it after partition changes so recovery keys stay valid.
Note your firmware: UEFI+GPT (any PC since ~2012) vs legacy BIOS+MBR. Install AcreetionOS in matching mode.

3. Install AcreetionOS alongside

In Calamares choose Manual partitioning: put / (+ swap or zram) into the free space, mount the existing EFI partition at /boot/efi WITHOUT formatting. Walkthrough: Partitioning.

4. Let GRUB find Windows

os-prober ships enabled; after install (or after Windows updates its bootloader):

sudo os-prober                       # expect a Windows Boot Manager line
sudo grub-mkconfig -o /boot/grub/grub.cfg
grep -i menuentry /boot/grub/grub.cfg | head

Missing? Ensure GRUB_DISABLE_OS_PROBER=false isn’t set in /etc/default/grub.

5. The clock war

Windows stores hardware clock as local time; Linux as UTC → hours drift. Fix on the Windows side (run as admin):

Reg add HKLM\SYSTEM\CurrentControlSet\Control\TimeZoneInformation /v RealTimeIsUniversal /t REG_DWORD /d 1

When Windows updates eat the boot menu

It sometimes reinstalls its own bootloader. Boot the AcreetionOS ISO → Recovery Environment → GRUB reinstall/boot repair → done, both entries restored.

Recovery partition note

The ACRECOVERY partition (The AcreetionOS Recovery Environment) coexists fine with dual-boots — it’s chainloaded from the main GRUB and never touches Windows entries.