Say you take a blank SD card, plug it into a computer. It may now appear as /dev/sdd. Let us now dump an image with two partition on this card

dd if=sdcard.img of=/dev/sdd bs=4M

Once this is done, we do not see /dev/sdd1 and /dev/sdd2 immediately.

Each time I did this, I had to take the card out of the slot and put it back in. Until I stumbled across this…

sudo /sbin/blockdev --rereadpt /dev/sdd

This re-reads the partition table without having to remove and re-insert the card.

Another solution I came across is -

sudo partprobe /dev/sdd

Yet another way -

sudo sfdisk -R /dev/sdd

I only found partprobe to work on mounted partitions. The others returned a partition busy error.