Bootable USB from the Terminal#

A bootable USB stick from an ISO — no extra tooling, just lsblk, umount and dd. The example writes a Debian netinst installer, but the steps are the same for any hybrid ISO. For what each command actually does, see lsblk, umount, dd, sync.

dd does not ask and has no undo. The wrong device name overwrites your system disk. Check the target twice before running it.

  1. Identify the device#

    lsblk -o NAME,SIZE,MODEL,TRAN,MOUNTPOINTS

    Example output:

    NAME        SIZE MODEL                   TRAN MOUNTPOINTS
nvme0n1     1.8T Samsung SSD
├─nvme0n1p1   1G                              /boot
└─nvme0n1p2 1.8T                              /
sdb        28.7G SanDisk Ultra          usb
└─sdb1     28.7G                              /run/media/xander/USB

    TRAN usb, the matching size and the model name identify the stick — here /dev/sdb.

  2. Unmount the partition#

    sudo umount /dev/sdb1

    Only the mounted partition has to go; the device itself is never mounted.

  3. Write the ISO#

    sudo dd \
  if="$HOME/Downloads/debian-13.6.0-amd64-netinst.iso" \
  of=/dev/sdb \
  bs=4M \
  status=progress \
  conv=fsync

    Adjust the ISO filename if needed. This gives you the exact name:

    ls -lh ~/Downloads/debian*.iso

  4. Flush the buffers#

    sync

    Only now is everything actually on the stick and safe to unplug.

Whole device, not the partition#

correct: /dev/sdb
wrong:   /dev/sdb1

Debian explicitly states that the ISO must be written to the complete drive, not to a single partition. A hybrid ISO carries its own partition table — write it inside an existing partition and the stick has no boot sector.

The dd options#

OptionMeaning
if=input file, the ISO
of=output file, the block device
bs=4Mblock size; without it dd copies in 512-byte chunks and takes forever
status=progressprogress output instead of silence
conv=fsyncflushes buffers to the device before exiting

conv=fsync technically makes the trailing sync redundant. It costs nothing and still helps if the ISO was written without that option.