Just using dd
and md5sum
/ sha1sum
is enough, but as previously said, be carefull, your device is not of the same size than your file, so sums will differ.
Here how you still can do it
First you'll need to know the size of the file:
$ stat -c '%s' debian-live-8.2.0-amd64-lxde-desktop.iso
1003487232
Then, to be cool with your syscalls, you better get this as a multiple of a nice power of two like 4096
, the multiplication of the two HAVE TO yield exactly the size of the file, in other ways, you'll check too few or too many bytes, yielding a wrong checksum.
$ bc
bc 1.06.95
scale = 9
1003487232 / 4096
244992.000000000
I'm happy, 4096 × 244992 = 1003487232
so 4096 is good for me, (and will for you, probably) so I can use a block size of 4096
(typical) and a bloc count of 244992
.
Don't forget to write the file on the USB key...
$ dd if=debian-live-8.2.0-amd64-lxde-desktop.iso of=/dev/sd? && sync
And know, using the known block size and the block count, you can read the exact number of bytes from the key and check them:
$ dd if=/dev/sdb bs=4096 count=244992 | sha1sum
b0dbe4ca8f526d1e43555459c538607d4a987184
(Yes md5sum
is way faster than sha1sum
but that's clearly not your bottleneck here, the bottleneck is the USB thoughput, thanks for noticing).
Or, in short:
dd if=/dev/sdb bs=4096 count=$(($(stat -c '%s' the.iso) / 4096)) | sha1sum