• Change to directory with .iso file you want to burn to bootable USB drive.
• Insert USB drive into Linux machine, it should mount if the drive is formatted as FAT32 (it will not recognize NTFS)
• Perform the following commands

dd if=ubuntu-18.04.2-desktop-amd64.iso of=/dev/sdg

If you wish to see the output/progress of the dd command, use status=progress or a pipe to the 'pv' utility, like this:

dd if=ubuntu-18.04.2-desktop-amd64.iso of=/dev/sdg status=progress

dd if=ubuntu-18.04.2-desktop-amd64.iso | pv | dd of=/dev/sdg

Notes:

• If USB drive has multiple partitions and you want a clean format, use Linux's gparted application (ex. gparted-0.33.0-1.el7.x86_64) to select the USB drive and do a FAT32 format on it.