Did you check it exists? ie. using
blkid (or equivalent) showed a sdb1 as a valid block device? capable of being mounted.
If you read the reference manual page for
man mount) you’ll see it refer to "special block device; as not all devices can be mounted the page refers to block devices as special as they can be mounted)
Thanx, I didn’t do that; I’ll do that now. I referred to Schott’s manual & the LinuxConfig w/s when I encountered the problem.
convenient to see all block devices.
And please make also sure, that the mountpoint /mnt/flash exists, before mounting.