How to create bootable USB drive from ISO image in Linux

ISO images are distributed in ISO 9660 format. The format is for optical discs, which could contain both data and the boot sector, making it bootable. Suppose you burn the ISO images directly into an external drive such as a USB stick or portable hard drive; you can directly boot from it.

ISO images are typically used to distribute operating system installers. The image should be bootable, automatically launching the operating system's installation program upon system boot.

Many Linux tools can be used to create a bootable USB drive from ISO image, and dd is the most universally available. dd is a command-line tool and is installed by default in most Linux distributions, such as Ubuntu, Fedora, CentOS, or SUSE.

1. Launch a terminal application.
2. Check if your image is in the correct ISO 9660 format and is bootable.

   $ file Downloads/ubuntu-21.04-desktop-amd64.iso 
   Downloads/ubuntu-21.04-desktop-amd64.iso: ISO 9660 CD-ROM filesystem data (DOS/MBR boot sector) 'Ubuntu 21.04 amd64' (bootable)

3. Check for currently available block devices.

   $ lsblk
   NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
   loop0    7:0    0 55.4M  1 loop /snap/core18/1997
   loop1    7:1    0  219M  1 loop /snap/gnome-3-34-1804/66
   loop2    7:2    0 64.8M  1 loop /snap/gtk-common-themes/1514
   loop3    7:3    0 32.3M  1 loop /snap/snapd/11588
   loop4    7:4    0   51M  1 loop /snap/snap-store/518
   loop5    7:5    0 65.1M  1 loop /snap/gtk-common-themes/1515
   sda      8:0    0   20G  0 disk 
   sdb      8:16   0   20G  0 disk 
   ├─sdb1   8:17   0    1M  0 part 
   ├─sdb2   8:18   0  513M  0 part /boot/efi
   └─sdb3   8:19   0 19.5G  0 part /
   sr0     11:0    1 1024M  0 rom

4. Insert your USB drive or stick and wait for a few seconds for it to be detected by the system.
5. Check for the device name of your newly inserted USB drive.

   $ lsblk
   NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
   loop0    7:0    0 55.4M  1 loop /snap/core18/1997
   loop1    7:1    0  219M  1 loop /snap/gnome-3-34-1804/66
   loop2    7:2    0 64.8M  1 loop /snap/gtk-common-themes/1514
   loop3    7:3    0 32.3M  1 loop /snap/snapd/11588
   loop4    7:4    0   51M  1 loop /snap/snap-store/518
   loop5    7:5    0 65.1M  1 loop /snap/gtk-common-themes/1515
   sda      8:0    0   20G  0 disk 
   sdb      8:16   0   20G  0 disk 
   ├─sdb1   8:17   0    1M  0 part 
   ├─sdb2   8:18   0  513M  0 part /boot/efi
   └─sdb3   8:19   0 19.5G  0 part /
   sdc      8:32   1 58.6G  0 disk 
   ├─sdc1   8:33   1  2.5G  0 part /media/user/Ubuntu 20.04 LTS amd64
   └─sdc2   8:34   1  3.9M  0 part /media/user/1079-24A3
   sr0     11:0    1 1024M  0 rom  

6. Make sure all the partitions of your USB drive is not mounted.

   $ sudo umount /dev/sdc1 /dev/sdc2
   [sudo] password for user:

7. Copy the ISO image to your USB drive using dd.

   $ sudo dd if=Downloads/ubuntu-21.04-desktop-amd64.iso of=/dev/sdc conv=fdatasync
   5505348+0 records in
   5505348+0 records out
   2818738176 bytes (2.8 GB, 2.6 GiB) copied, 628.961 s, 4.5 MB/s

   Related: How to monitor progress of dd command

8. Check if ISO image successfully copied to your USB drive.

   $ sudo blkid /dev/sdc
   /dev/sdc: BLOCK_SIZE="2048" UUID="2021-04-20-11-16-16-00" LABEL="Ubuntu 21.04 amd64" TYPE="iso9660" PTUUID="af8737a9-1e23-4373-b87a-c8b16199d461" PTTYPE="gpt"

9. Disconnect your USB drive from your machine.