Managing Windows and Linux bootloaders

A proper way resize partition on dualboot Windows and Linux System

I would never risk managing a live system without backups. So we need 2 flashdrives. And running dualboot system with Linux and Windows.

Prepare flash drives:

Linux

Boot from Linux. Downloads archlinux.iso and flash it to a 1st flash drive.

dd if=./archlinux.iso of=/dev/sdX bs=4096 status=progress

Please choose sdX carefully, it should be your flash drive, not your root system, neither specific partition like /dev/sda1.

Windows

Boot from windows. Google download windows 11 and select Create Windows 11 Insallation Media. Currently it’s here Flash it to the 2nd flash drive.

Backup

I would recommend using any other harddrive or flash drive to backup current system. Inject Linux flash drive into PC, go to BIOS and select boot from flash

Boot from your Linux flash drive, and mount the place you want to back up your FS.

mkdir /mnt/bu
mount /dev/sdX /mnt/bu

I would recommend backing up the whole disk, if you have enough space

dd if=/dev/sdX of=/mnt/bu/sdX bs=4096 status=progress

bs=4096 requires, otherwise copying would be byte by byte and really slow.
status=progress informs your about how much time it will take.
if=/dev/sdX your disk that you want to backup.
of=/mnt/bu/sdX the path you want to backup, where sdX is just a name of the file on filesystem

Verify that file is backed up properly. You can load partitions from the backed file /mnt/bu/sdX with

losetup --show -P -f /mnt/bu/sdX

After this command you will have files like /dev/loop1p1 that you can mount if needed. THey will contain your partition backed up data.

If you need to back up specific files and exclude some of them you have to traverse FS. Example of backing up everything in /mnt/source/* to /mnt/target_root/ excluding /mnt/source/home/andrew. Note /mnt/source/ has the trailing slash in order to avoid creating source directory in target_root and home/andrew is relative to source directory.

rsync -a --exclude='home/andrew' --links /mnt/source/ /mnt/target_root/

Restructure your partitions

I personally like using cfdisk. It’s much more intuitive than fdisk, and much more broad than other cli or even GUI applications. Do any operation that’s required for you.

cfdisk /dev/sdX

If you increased the size of your partition you’ll need to tell the fs to make use of a new space. This is for ext4 fs.

resize2fs /dev/sdX1

Do not forget to leave or recreate EFI filesystem and if you have Windows, all partitions that it has. I would recommend dd them back and resize after, instead of copying files with cp -rp

You can use losetup to load partition table from the file like above.

There are 2 ids that are used in file systems:

Disk GUID. Which is a single for all disk and not relevant to us.
Partition GUID, which is alway a UUID (36 base_16 characters) in GPT
Volume Serial Numer. E.g. NTFS is 16 base_16 characters
There’s also a filesystem type id to detect whether it’s NTFS or Ext. Not relevant to us

When you copy a partition with dd it will clone the partition Volume Serial Number. Which is a desired outcome if we want to keep same configuration of fstab or window disk conf. Also eject or erase your old partition since you don’t wanna have 2 identtical Volume IDS in the OS. AS for partition GUID it can have new id, in this case WIndows Bootloader should be fixed which is described below

Fix windows bootloader

Inject flash drive with windows, select it from the BIOS and boot from it.

Go to restore windows, and Use CLI.

Assign letter

Mount old drive C to letter K. In the command below replace disk 0 and partition 2 to your partition and disk

> diskpart
DISKPART> list disk
DISKPART> select disk 0
DISKPART> list part
DISKPART> select partition 2
DISKPART> assign letter=K

Mount UEFI partition to letter L. In the command below replace disk 0 and partition 2 to your partition and disk

DISKPART> select disk 1
DISKPART> list part
DISKPART> select partition 3
DISKPART> assign letter=L
DISKPART> exit

Fix bootloader

From the cli tell the UEFI that you want to add new Windows 11 OS.

> bcdboot K:\Windows /s L: /f UEFI

Now you should be able too reboot your PC and be able to boot from windows. Check if BIOS contains the proper Windows loader.

Remove old Windows entry

During Windows boot you might experience choosing the proper OS. You can remove the old one by going to msconfig.

Press Win+R, type msconfig and hit enter
Select BOOT tab
Remove the old Windows entry. The one that is currently in use, gonna be called C:. You need to keep that. Another one you are free to remove

Fix Linux bootloader

Inject Linux flash drive, you might required to go to BIOS and select flash drive to boot from.

Mount root partition, arch-chroot into it, fix bootloader with bootctl install.

mount /dev/sda4 /mnt
arch-chroot /mnt

Edit fstab and fix the path to your partitions

vim /etc/fstab

Mount boot now and fix its loader. Remember you are still in chrooted system

mount /boot

Fix bootloader entry. I’m using SystemDBoot. For systemD you do:

vim /boot/loader/entries/arch.conf

Or w/e path you have your configs

Don’t forget to install bootloader to UEFI now. Verify that UEFI mode is avaiable:

efivar --list

And install the loader again

bootctl install

Select Linux bootloader from BIOS.