Convert a bootable USB to normal

 Search 'Discs' In Ubuntu ,from applications, to get the name of the partition

sudo wipefs --all /dev/sdb

Now, the filesystem has been wiped and the flash drive is completely clean. You can check that with: 

 

sudo fdisk -l

ou should see that the USB flash device has no partition. You need to create one. 

Create the new partition using the command line

sudo cfdisk /dev/sdb

 

Format the USB drive with FAT

sudo mkfs.vfat -n 'ALU' /dev/sdb1