Making USB Media on Linux
- Connect a USB flash drive to the system and execute the dmesg command. A log detailing all
recent events will be displayed. At the bottom of this log, you will see a set of messages caused
by the USB flash drive you just connected. It will look like a set of lines similar to the following:
[ 170.171135] sd 5:0:0:0: [sdb] Attached SCSI removable disk
Note the name of the connected device – in the above example, it is sdb.
- Log in as root:
$ su –
Provide your root password when prompted.
- Make sure that the device is not mounted. First, use the findmnt device command and the
device name you found in the earlier steps. For example, if the device name is sdb, use the
If the command displays no output, you can proceed with the next step. However, if the
command does provide output, it means that the device was automatically mounted and you
must unmount it before proceeding. A sample output will look similar to the following:
TARGET SOURCE FSTYPE OPTIONS
/mnt/iso /dev/sdb iso9660 ro,relatime
Note the TARGET column. Next, use the umount target command to unmount the device:
- Use the dd command to write the installation ISO image directly to the USB device:
#dd if=/image_directory/image.iso of=/dev/device bs=blocksize
Replace /image_directory/image.iso with the full path to the ISO image file you downloaded,
device with the device name as reported by the dmesg command earlier, and blocksize with a
reasonable block size (for example, 512k) to speed up the writing process. The bs parameter is
optional, but it can speed up the process considerably.
Make sure to specify the output as the device name (for example, /dev/sda), not
as a name of a partition on the device (for example, /dev/sda1).
For example, if the ISO image is located in /home/testuser/Downloads/rhel-server-7-x86_64-
boot.iso and the detected device name is sdb, the command will look like the following:
#dd if=/home/testuser/Downloads/rhel-server-7-x86_64-boot.iso of=/dev/sdb bs=512k
- Wait for dd to finish writing the image to the device. Note that no progress bar is displayed; the
data transfer is finished when the # prompt appears again. After the prompt is displayed, log out
from the root account and unplug the USB drive.