Making Installation USB Media on Linux

The following procedure assumes you are using a Linux system and that you have downloaded an appropriate ISO image as described in Downloading CentOS. On most Linux distributions, it will work without the need for installing any additional packages.

This procedure is destructive. Any data on the USB flash drive will be destroyed with no warning. Make sure that you specify the correct drive, and make sure that this drive does not contain any data you want to preserve.

Many Linux distributions provide their own tools for creating live USB media, for example, usb-creator on Ubuntu. Describing these tools is beyond the scope of this book; the following procedure will work on most Linux systems.

Making USB Media on Linux
  1. 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.

  2. Log in as root:

    $ su -

    Provide your root password when prompted.

  3. 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 following command:

    # findmnt /dev/sdb

    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:

    # findmnt /dev/sdb
    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:

    # umount /mnt/iso
  4. 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/CentOS-server-x86_64-boot.iso and the detected device name is sdb, the command will look like the following:

    # dd if=/home/testuser/Downloads/CentOS-server-x86_64-boot.iso of=/dev/sdb bs=512k
  5. 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.

The USB drive is now ready to be used as a boot device. You can continue with Booting the Installation on 64-bit AMD, Intel, and ARM systems on AMD, Intel, and ARM systems, or Booting the Installation on IBM Power Systems on IBM Power Systems servers.

Non-virtualized installations (known as "bare metal" installations) on IBM Power Systems servers require that the inst.stage2= boot option is specified. Refer to Configuring the Installation System at the Boot Menu for information about the inst.stage2= boot option.