A second system on the same disk is an hour of work with three real risks: no free space, a broken bootloader and a Windows partition nobody backed up.
Back up first, shrink Windows from a **Linux live system** with **GParted**, install Linux into the free space and pick **Install alongside**. Windows stays intact as long as you never format its partition.
Copy everything you cannot lose to an external drive. If the Windows drive is encrypted, suspend protection before touching partitions and keep the recovery key within reach for the whole session.
Open Disk Management and note the partition style: GPT with an EFI partition, or the older MBR. The installer needs unallocated space at the end of the disk, not a second partition you formatted by hand.
diskmgmt.mscWindows shrinks only up to the last immovable file, often far less than expected. Boot the live USB, open GParted and resize the Windows partition from outside, where no file is locked.
Boot the installer and pick **Install alongside Windows**. It detects the free space and creates its own root partition plus a swap file. Manual partitioning works too, but only when you know which partition is which before you start.
After the first boot, list the firmware entries and confirm both systems appear. GRUB should offer Windows, and a firmware menu entry pointing at the right loader is a useful fallback if it does not.
sudo efibootmgr -v
sudo update-grubSet the default entry in GRUB, then reboot into each system two times in a row. A boot that works once and fails after a Windows update is a known failure mode, and knowing where to repair it saves an evening.
sudo nano /etc/default/grub
GRUB_DEFAULT=0os-prober is disabled on several distributions. Enable it in /etc/default/grub and regenerate the configuration.
Windows was hibernated, not shut down. Disable Fast Startup in the power settings and boot it once cleanly before trying again.
One system uses local time, the other UTC. Set Linux to local time or make Windows use UTC with the RealTimeIsUniversal registry value.
The shrink hit an immovable file. Disable hibernation and the page file, then retry the resize from the live system.
A second SSD is safer and simpler: unplug the Windows drive during install and nothing can go wrong.
No. The Windows partition is not modified; the installer only uses the free space around it.
Boot Windows, delete the Linux partitions in Disk Management and extend the Windows partition back into the space. Remove the Linux entry with efibootmgr if it stays in the firmware menu.
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