For systems without CD drive, the NixOS live CD can be booted from a USB stick. For non-UEFI installations, unetbootin will work. For UEFI installations, you should 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).