Install Windows after Ubuntu/Linux
October 11, 2017
As you know, the most common, and probably the most recommended way of dual booting Ubuntu and Windows is to install Windows first and then Ubuntu. But what if you want to install Windows second on a computer with Ubuntu/Linux already installed?
This guide assumes that you have Ubuntu already installed on your system, and will guide you through installing Windows 7/8/8.1/10 when you have a working Ubuntu/Linux partition.
The problem here is that the Windows installer tends to overwrite Grub bootloader or whatever making only the Windows installation bootable. But the good news is that your Linux partition is untouched, including the original bootloader and the other Grub configurations. So restoring or recovering the Grub is just a matter of running a few commands on the terminal.
Install Windows on a Separate Partition
If your Ubuntu installation occupies the entire hard drive, to be able to create free space for the Windows installation, you may have to shrink an existing partition using a disk utility like GParted. GParted comes preinstalled on Ubuntu LiveCD.
Boot into a Windows installation media and complete with the installation
Once installed, because of Microsoft’s false assumption that there are no non-Microsoft operating systems you’ll be taken straight into Windows.
Restore / Reinstall Grub 2 with a Ubuntu Live Media
- Now boot into a Ubuntu Live/USB or CD.
- Open a terminal. (Ctrl + Alt + t)
- Use lsblk, blkid commands or GParted to identify your Linux root, and boot partitions. You may or may not have a separate boot partition.
Find Linux Partitions
$ lsblk -f NAME FSTYPE MOUNTPOINT sda ├─sda1 ext4 /boot ├─sda2 ext4 / ├─sda3 ntfs
In my case,
/dev/sda1is the Linux boot partition
/dev/sda2is the Linux root partition
/dev/sda3is the Windows partition
Setup a Chroot Environment
Now we’ll be repairing our old grub bootloader in a chroot environment.
Mount your root filesystem under
sudo mount /dev/sda2 /mnt/
If you’re using BTRFS (New Linux B-Tree File System) instead of EXT4, the above command should change to sudo mount -t btrfs -o subvol=@ /dev/sda2 /mnt/
ls /mntto verify that the correct partition is mounted. It should list the content of your root.
$ ls /mnt bin dev home lib64 media opt root sbin sys usr vmlinuz boot etc initrd.img lost+found mnt proc run srv tmp var vmlinuz.old
Mount the boot partition. (SKIP if you don’t have a separate boot partition)
sudo mount /dev/sda1 /mnt/boot
If you have an EFI partition you should mount that also. It is basically a small FAT32 partition around 100mb. Please refer to the section on how to reinstall Grub in an EFI system.
Bind the directories, so grub can detect other operating systems, like so.
sudo mount --bind /dev /mnt/dev sudo mount --bind /dev/pts /mnt/dev/pts sudo mount --bind /proc /mnt/proc sudo mount --bind /sys /mnt/sys
Let’s chroot into our existing Ubuntu/Linux system on the hard disk.
sudo chroot /mnt
grub-install /dev/sda (specify the disk `/dev/sdX`, not `/dev/sdaX`) grub-install --recheck /dev/sdX exit
Once you’ve successfully reinstalled Grub, restart the computer. On next reboot Grub will be the default bootloader and you’ll be presented with a list of operating systems to choose from (Ubuntu and Windows, of course).
Reinstalling Grub in an EFI Based System
Reinstalling Grub bootloader in a UEFI based computer is no different from installing Grub on a legacy Bios system. Here we also mount the EFI partition before chrooting, as we’d do with the boot partition.
$ lsblk -f NAME FSTYPE MOUNTPOINT sda ├─sda1 ext4 /boot/efi ├─sda2 ext4 / ├─sda3 ntfs
/dev/sda1 is the EFI partition and
/dev/sda2 is the root.
sudo mount /dev/sda2 /mnt/ ( For BTRFS: sudo mount -t btrfs -o subvol=@ /dev/sda5 /mnt/ )
Mount EFI partition under ‘/mnt/boot/efi’
sudo mount /dev/sda2 /mnt/boot/efi
Forgetting to do so will result in errors being thrown while trying to execute grub-install: “/boot/efi does not appear to be the EFI partition”
As shown previously, bind the
sudo chroot /mnt grub-install exit
In some rare occasions, Grub might not detect Windows. In that case just login to Ubuntu (installed one on the disk, not the bootable Live USB/CD) and execute,
sudo os-prober sudo update-grub sudo reboot