Check the disks present on the server:

lsblk -o NAME,SIZE,FSTYPE,TYPE,MOUNTPOINT

Example:

NAME SIZE FSTYPE TYPE MOUNTPOINT
sda 5.5T disk
sdb 5.5T disk
sdc 5.5T disk
sdd 5.5T disk
nvme0n1 477G disk
├─nvme0n1p1 511M vfat part /boot/efi
├─nvme0n1p2 476G ext4 part /
├─nvme0n1p3 512M swap part [SWAP]
└─nvme0n1p4 2M iso9660 part

Creating RAID 5 array (we will use it to store the backups):
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Step 1:

cp -pv /etc/apt/sources.list /etc/apt/sources.list.bak

Step 2, replacing OS name in the sources.list file:

nano /etc/apt/sources.list

Before:
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