partprobe (from the parted package) informs the kernel that a disk's partition table changed so new partitions appear without a reboot.

sudo partprobe /dev/sdc            # re-read one disk
sudo partprobe                      # all devices

Print a summary without telling the kernel anything (dry run):

sudo partprobe -d -s /dev/sdc
/dev/sdc: msdos partitions 1 2

If it fails with "device busy", something on that disk is still mounted or in use. Unmount it first. Alternatives: sudo blockdev --rereadpt /dev/sdc (see blockdev), sudo partx -u /dev/sdc, or kpartx for image files. After partitioning, wait for udev with sudo udevadm settle.