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Creating an Emergency Boot Device for QFX Series Switches


If Junos OS on the device is damaged in some way that prevents the software from loading properly, you can use an emergency boot device to repartition the primary disk and load a fresh installation of Junos OS. Use the following procedure to create an emergency boot device.

Before you begin, you need to download the installation media image for your device and Junos OS release from .


You can create the emergency boot device on another Juniper Networks switch or router, or any laptop or desktop PC that supports Linux. The steps you take to create the emergency boot device vary, depending on the device.

To create an emergency boot device:

  1. Use FTP to copy the installation media image into the /var/tmp directory on the device.
  2. Insert a USB storage device into the USB port.
  3. From the Junos OS command-line interface (CLI), start the shell:
    user@device> start shell
  4. Use the gunzip command to unzip the image file.
  5. Switch to the root account using the su command:
    % su
    Password: password

    The password is the root password for the device. If you logged in to the device as the root user, you do not need to perform this step.

  6. Enter the following command on the device:
    root@device% dd if=/var/tmp/filename of=/dev/da1 bs=1m

    The device writes the installation media image to the USB storage device:

  7. Log out of the shell:
    root@device% exit
    % exit