The partition-number is determined by the partition-table entry. Deleting the first partition, in fact means to delete the first partition-table entry. the remaining second partition is still defined by the second partition-table entry, thus it's number is still 2.

There is not really a need to change that, if your partition is defined by the first or second partition-table entry does not matter, in real life you will rarely see your partition number, there is no impact on performance. Reordering your partition-table entries comes with some risk, you may accidentally enter wrong commands.

There is a chance that grub will be broken (since grub uses UUID to find correct partitions I wouldn't expect that, but be prepared to eventually have to reinstall grub).

If you've made any changes to /etc/fstab and use /dev/sda2 instead of UUID, you'll have to change that as well.

I recommend not to do this change, there is no advantage you could gather.

If you really inist in doing that change, here we go:

Use your installer-USB to Try without installing and perform the action from this session, your partition has to be unmounted!

Recheck the correct drive with lsblk -f to see if /dev/sda is still the correct drive, it may or may not change when booted from installer. You'll have to adapt the devicename in the following commands depending on the output you got from the lsblk-command.

Create a copy of the partition-table:

~$ sudo sfdisk -d /dev/sda > sdatable

The result looks like this:

~$ cat sdatable

label: gpt

label-id: CAEC9287-6E64-48BD-8223-B951EE4C7345

device: /dev/sda

unit: sectors

first-lba: 34

last-lba: 625142414

sector-size: 512



/dev/sda2 : start=        2048, size=   625131520, type=0FC63DAF-8483-4772-8E79-3D69D8477DE4, uuid=917D415A-7E8F-C74E-8D72-1259A7C02ED6, name="archiv"

Now edit only the start of the last line from /dev/sda2 to /dev/sda1, leave anything else as it is. I used nano to do this. The last line should now look like this:

/dev/sda1 : start=        2048, size=   625131520, type=0FC63DAF-8483-4772-8E79-3D69D8477DE4, uuid=917D415A-7E8F-C74E-8D72-1259A7C02ED6, name="archiv"

In the next step load the altered copy of the partition-table:

~$ sudo sfdisk --force /dev/sda < sdatable

Checking that no-one is using this disk right now ... OK



Disk /dev/sda: 298.09 GiB, 320072933376 bytes, 625142448 sectors

Disk model: Hitachi HTS54503

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disklabel type: gpt

Disk identifier: CAEC9287-6E64-48BD-8223-B951EE4C7345



Old situation:



Device     Start       End   Sectors   Size Type

/dev/sda2   2048 625133567 625131520 298.1G Linux filesystem



>>> Script header accepted.

>>> Script header accepted.

>>> Script header accepted.

>>> Script header accepted.

>>> Script header accepted.

>>> Script header accepted.

>>> Script header accepted.

>>> Created a new GPT disklabel (GUID: CAEC9287-6E64-48BD-8223-B951EE4C7345).

/dev/sda1: Created a new partition 1 of type 'Linux filesystem' and of size 298.1 GiB.

Partition #1 contains a ext4 signature.

/dev/sda2: Done.



New situation:

Disklabel type: gpt

Disk identifier: CAEC9287-6E64-48BD-8223-B951EE4C7345



Device     Start       End   Sectors   Size Type

/dev/sda1   2048 625133567 625131520 298.1G Linux filesystem



The partition table has been altered.

Calling ioctl() to re-read partition table.

Syncing disks.

Rechecking with lsblk gives as expected

~$ lsblk -f | grep sda

sda                                                                                        

└─sda1 ext4     1.0   archiv           57d76d02-deb6-47cf-bb2d-5da748f1cc38

Done. Do it on your own risk!