Distros : Prep - dd: Flash
dd is a command line tool to convert and copy files, would have been called cc but that name was already taken.
One common application is to burn an ISO image onto a USB key, just make sure that the USB key is same size or bigger than the ISO. In effect the USB key becomes identical to the ISO.
In the case below I am running Puppy Linux, I booted from a USB key and did a cd to a folder on a laptop's hard drive where I used wget to downloaded an ISO to.
Sticking in a USB Key that I want to burn the image onto I got a pop up message from puppy which tells me that the USB key is seen as /dev/sdc
This makes sense, the Hard Drive is /dev/sda, the Puppy USB key is /dev/sdb and the new device is /dev/sdc.
To double check that, I ran the command dmesg | tail
which displays system messages and that command is piped to tail which by default will display the last 10 lines and yes sdc
shows up in the last 7 events so the target for dd is definitely /dev/sdc.

Now for the dd
command..
dd if=firmware-10.9.0-amd64-i386-netinst.iso of=/dev/sdc bs=64k status=progress
Lets break down that command..
if=
is the input file in this case a Debian network install ISOof=
is the output file, where the image will be written to, make sure that this is correctbs=
is block size which by default is 512 Bytes, takes forever, I searched the net for the optimum block size, most hits suggest 64KB, so to state that in the dd command bs=64kstatus=progress
will cause dd to display what's going on and give you some idea of time remaining, otherwise you will get no output from the command until it's finished.
Be careful when using dd
make sure that the output is correct, if I mistakenly put of=/dev/sda
the ISO would be installed onto my Hard Drive, OH NOOOOO and all other data on that partition WOULD BE WIPED.
Also be sure to allow dd
to finish, otherwise the image will be incomplete and you wont be able to boot from it.
If you feel nervous about using dd (and you should) try out Rufus if using Windows or check out Etcher which will work on Windows, Apple and Linux!!