How to test that your usb live cd is working

To do this, you need qemu-kvm. Install it:
$ sudo apt install qemu-kvm


Check the address of your usb, by using dmesg
$ dmesg | grep sd


Once you have the address, you can start it using below command (make sure you allocate at least 1024M memory, else it will return kernel panic)
$ sudo qemu-system-x86_64 -m 1024 -hda /dev/sdb


To use a cdrom, you can use below command
$ sudo qemu-system-x86_64 -m 1024 -cdrom /dev/cdrom


You can also test an iso file, using below command
$ sudo qemu-system-x86_64 -m 1024 -cdrom centos.iso