For systems without CD drive, the NixOS live CD can be booted from a USB stick. You can use the dd utility to write the image: dd if=path-to-image of=/dev/sdb. Be careful about specifying the correct drive; you can use the lsblk command to get a list of block devices. The dd utility will write the image verbatim to the drive, making it the recommended option for both UEFI and non-UEFI installations. For non-UEFI installations, you can alternatively use unetbootin. If you cannot use dd for a UEFI installation, you can also mount the ISO, copy its contents verbatim to your drive, then either: Change the label of the disk partition to the label of the ISO (visible with the blkid command), or Edit loader/entries/nixos-livecd.conf on the drive and change the root= field in the options line to point to your drive (see the documentation on root= in the kernel documentation for more details).