Change partition order - replace sda1 wih sda2 and so on, renumber partitions

Suppose you have this layout:

/dev/sda1 - /
/dev/sda2 - /boot

You now want to have the boot partition before /:

/dev/sda1 - /boot
/dev/sda2 - /

But you want to keep the UUID:s of the partitions, so the UUID of sda1 gets transferred to sda2.

Some things to note here:
- sdaX numbers seems to be just the order of the partitions on the disk.
- UUID:s are noted in the partitions, copying the contents of one partition to another results in a duplicate UUID.
- Grub mostly seems interested in where the boot flag is situated, it checks this partition for initrd:s.
- Initramfs (located in /boot) is built with /etc/fstab, /etc/crypttab.

Boot Gparted live ISO (0.28+ for LUKS encrypted partition support).

If you have encrypted partitions, you may need to open a terminal and unlock them:
cryptsetup luksOpen /dev/sda2 /dev/sda2_crypt

Alternative 1 - copying using Gparted

Cut and paste the partitions in Gparted, it seems to keep the UUID on both the original and the copy.

Alternative 2 - copying using Gparted and dd

Shrink the partitions in Gparted to minimal sizes, note that you may need to reduce in pieces to get through, first reduce 25%, then 25% again and so on. Also remember that Ext4 partitions has 5% reserved free space for system files if not disabled using tune2fs.

Create a new third partition behind /dev/sda2 (/boot) at a size covering /dev/sda1 (/), this will be /dev/sda3.

Then open a terminal and copy the contents of /dev/sda1 to /dev/sda3:
sudo bash
dd if=/dev/sda1 of=/dev/sda3 bs=1024k status=progress

Ensure /dev/sda2 fits in /dev/sda1, if not, resize. Then copy /dev/sda2 to /dev/sda1:
dd if=/dev/sda2 of=/dev/sda1 bs=1024k status=progress

Then remove /dev/sda3 in Gparted, resize and set the boot flag on /dev/sda1.

Mount and update references

For regular root partition:
mount /dev/sda2 /mnt

For LUKS encrypted root partition:
cryptsetup luksOpen /dev/sda2 /dev/sda2_crypt
mount /dev/mapper/sda2_crypt /mnt

mount /dev /mnt/dev
mount -t proc proc /proc
mount -o bind /dev /mnt/dev
mount -o bind /dev/pts /mnt/dev/pts
chroot /mnt
mount -t sysfs sys /sys

Check /etc/fstab, if there are any /dev/sdaX notations there then change them.

Edit /etc/crypttab so the sdaX_crypt lines are correct.

Go to /boot/, remove initrd files, then regenerate them:
update-initramfs -c k all

grub-install /dev/sda
update-grub

To be on the safe side it may be wiseable to repeat one time from update-initramfs.

There may be more locations in /etc/ to change /dev/sda1 to /dev/sda2 and vice versa, to check in all files there do:
cd /etc
grep -rn "put-sda1-or-sda2-here" --color=auto ./

Change partition numbers, renumber partitions

Suppose you have this situation:

/dev/sda2
/dev/sda3

And you want:

/dev/sda1
/dev/sda2

The do the following - sdX here is sda, sdXY is the root partition

Dump the partition table:
sfdisk -d /dev/sdX > sdX.out

Take a backup of it
cp sdX.out sdX.backup

Open the file sdX.out in an editor like vi and change the numbers on the sdXY lines.

Overwrite the old partition table with the edited one
sfdisk /dev/sdX < sdX.out

If it fails, revert to the backup:
sfdisk /dev/sdX < sdX.backup

Repair grub:
mount /dev/sdXY /mnt
mount -t proc proc /mnt/proc
mount -o bind /dev /mnt/dev
mount -o bind /dev/pts /mnt/dev/pts
chroot /mnt
mount -t sysfs sys /mnt/sys
update-grub
grub-install /dev/sdX
exit
reboot

Source: https://unix.stackexchange.com/questions/18752/change-the-number-of-the-partition-from-sda1-to-sda2