After I upgraded to Ubuntu 21.04, my TmpUsb script suddenly started reporting the following
hexdump: stdin: Illegal seek.
Line causing issue was the one determining partition serial number:
dd if=/dev/sda bs=512 skip=1 count=1 | hexdump -s39 -n4 -e '4/1 "%02X"'
It seems that
hexdump got a bit too stricter with its input parameters and now disallows skipping bytes in fifo stream. I haven’t investigated much but my guess is that skipping 39 bytes probably messes with its internal buffer. In any case,
dd has no such issues so the same code can be done without skipping in
dd if=/dev/sda bs=1 skip=551 count=4 | hexdump -n4 -e '4/1 "%02X"'`
The best part is that this is compatible with older versions too.