There are a lot of backup utilities available, but the simplest backup tool is available already with every single Linux distribution out there. The 'dd' tool simply copies standard input to standard output, read in 512-byte blocks.
With this, dd can copy a file to another file, or a partition to another partition, or file to partition (and vice versa). This makes dd quite versatile, and perfect for cloning partitions and drives. For instance, to make an exact clone of the /boot partition to a backup file, you could use:
# dd if=/dev/sda1 of=/srv/boot.img