'if': input file, e.g. if=/dev/sda
'of': output file, e.g. of=/home/duncan/Documents/backup.img
'bs': block size, the size of the blocks to copy, e.g. bs=256k (I never saw
any speed benefits for different values, however see
https://stackoverflow.com/questions/2787330/dd-block-size-optimisation)
'conv': according to Wikipedia, "The noerror option means to keep going if
there is an error, while the sync option causes output blocks to be padded."
So I just use the noerror option.
So an example dd command could be
dd if=/dev/sda of=/home/myself/Documents/backup.img bs=256k conv=noerror
Then I might restore the disk image (it does work, I once restored with dd
after something went wrong).
dd if=/home/myself/Documents/backup.img of=/dev/sda bs=256k conv=noerror
However, you will need to do this from a different OS. For example, I might
install Trisquel on a different HDD, and then use the dd command from it to
backup/restore. You could also use a live CD/DVD or live USB to copy the disk
image to an external HDD. However the large disk space needed might make it
more desirable to use the normal backup/restore option. You should also be
careful not to get the 'if' and 'of' options mixed up!
