dd

'dd' is a powerful command-line program that's been a staple of UNIX operating systems since the 1980s.

Pros:

• Ubiquitous on all UNIX-like operating systems
• When you use Linux, macOS or BSD, 'dd' will be available.
• Extremely powerful options for advanced users
• You can copy exactly blocks that want to exactly where you want (using the options like count=, bs=, seek=, skip=).
• The manual is of course invaluable with this: man dd

Cons:

• Very esoteric interface
• dd predates standard UNIX options syntax like mkdir -p, so the option syntax is weird
• No progress bar (see Tips section below)
• A single typo can destroy your data
• Always use eg, fdisk -l /dev/sda to check your device node, because dd if=my_linux.iso of=/dev/sda could end up overwriting an important disk!
• 'dd' is affectionately called "Disk Destroyer" for a reason!
• Default block size makes transfers very slow by default (see Tips section below)
• Not robust to bad sectors
• The standard dd command is not very good at handling clusters of bad sectors within dying optical media and hard drives. For such disks, look at GNU ddrescue: GNU ddrescue

Tips:

• Set the default block size to vastly speed up your transfers
• Try setting bs=1M to set a 1 megabyte block size and see if it speeds up your transfer!
• Consider periodically send a USR1 signal to request dd to print statistics
• On Linux machines, after you start your transfer switch to a new terminal and simply run the following to make dd print statistics each second:
• watch -n 1 kill -USR1 `pgrep dd`
• On BSD and macOS, send the INFO signal

For users new to 'dd' this may all seem overwhelming. If all you're looking to do is flash a Linux ISO image onto a USB stick and move on with your life then there are definitely much easier applications.

But there is a reason dd has been around for so many decades. It's simply extremely powerful, versatile and ubiquitous.