Dd

Create bootable USB from ISO image

Find out name of USB drive.

lsblk

Make sure that it is not mounted. Run command below, replacing /dev/sdx with your drive (do not append a partition number, do not use something like /dev/sdb1).

dd bs=4M if=/path/to/archlinux.iso of=/dev/sdx status=progress oflag=sync

Create swapfile and activate it

Create a 1 GiB file in the current dir to be used as swap space and give it appropriate format and permissions.

sudo dd if=/dev/zero of=swapfile bs=1024 count=1048576

sudo chmod 600 swapfile

sudo mkswap swapfile

Add the file to the current swap area.

sudo swapon swapfile

Add an entry to /etc/fstab so the file is used automatically after boot.

/path/to/swapfile  swap  swap  defaults  0  0

Save disc contents as ISO file

Verify if the cd is mounted.

mount

If it is, unmount it.

sudo umount /dev/cdrom

Create ISO image.

sudo dd if=/dev/cdrom of=/tmp/cdimg1.iso