dd

dd, a.k.a. disk destroyer.

flash an external device (e.g. flash drive or SD-card)

Double-check device names! Writing an image to the wrong device will result in disaster and data loss.

1. Insert external device.
2. Run lsblk to identify the device. If you can't tell from the device sizes, compare the output of lsblk when the device is not plugged in to when it is.

3. Unmount the external device you want to flash to with

   sudo umount /dev/<mounted_partition>
   

4. Run

   sudo dd if=/path/to/image.img of=/dev/<device_name> bs=4M conv=fsync status=progress
   

5. Remove external device once dd is finished.