How we create bootable GNU/Linux USB flash drives from terminal

A very important tool in our everyday life are the LiveUSB GNU/Linux flash drives.
We keep an updated collection of several GNU/Linux flavors/distributions (Fedora, CentOS, (L/X)Ubuntu, Kali etc.) that are used depending on the scenario.

The command we use is the following:

sudo dd bs=4M if=path/to/OS.iso of=/dev/sdX conv=fdatasync;

dd allows you to convert and copy a file and we use it to copy the ISO file of the operating system onto the USB flash drive.


  1. You need to unmount the USB flash drive before formatting it, e.g.:
    sudo umount /dev/sdXY;
  2. You need to use the device filename and not a partition filename:
    e.g. You need to use /dev/sdX and NOT /dev/sdX1
  3. You need to use either the root account or execute the command with sudo
  4. If you do not know the filename associated with your flash drive, use an application like the following ones to determine which /dev file is mapped to the USB flash drive:
    gnome-disks; or
    lsblk; or
    sudo fdisk -l;

The parameters we use are the following:

  • bs=SIZE_IN_BYTES defines up to how many bytes should be read and written at a time.
    In our case we used 4 Megabytes (4M).
  • if=INPUT_FILE defines the file to be read, we use this parameter to point to the OS ISO file that we want to write on the USB drive.
  • of=OUTPUT_FILE defines the filename where the data is to be written in.
    In GNU/Linux, devices are accessible like files as well so we used /dev/sdX here that happened to be the device file assigned to our USB device.
  • conv=CONVS converts the file as per the comma separated symbol list
    fdatasync physically writes output file data before finishing, we use this parameter to be sure that all I/O operations are done well before dd terminates, this way we are certain that our USB device will be ready to use as soon as the application is done.

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