sample
dd if=2017-11-29-raspbian-stretch-lite.img of=/dev/mmcblk0 bs=4M conv=fsync status=progress
progress copy or dd | dd cheat
dd if=/dev/urandom of=/dev/null status=progress bs=1G count=1 oflag=direct
dd if=/dev/urandom | pv | dd of=/dev/null- bs : sets the if and of sizes to bytes; block size (base 10 integer, 1G=1024×1024×1024 bytes = 1.073 GB);
- count : number of blocks (1 means that 1 block of 1G is copied);
- oflag=direct : uses direct I/O data, avoiding the buffer cache; it speeds up the process