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Understanding How the Primary Junos OS Image with Dual-Root Partitioning Recovers on the ACX Series Router

If the ACX Series Universal Access router is unable to boot from the primary Junos OS image and boots up from the backup Junos OS image in the backup root partition, a message appears on the console at the time of login indicating that the device has booted from the backup Junos OS image.

    login: user

    Password:

    ***********************************************************************

    **                                                                   **

    **  WARNING: THIS DEVICE HAS BOOTED FROM THE BACKUP JUNOS IMAGE      **

    **                                                                   **

    **  It is possible that the active copy of JUNOS failed to boot up   **

    **  properly, and so this device has booted from the backup copy.    **

    **                                                                   **

    **  Please re-install JUNOS to recover the active copy in case       **

    **  it has been corrupted.                                           **

    **                                                                   **

    ***********************************************************************

Because the system is left with only one functional root partition, you should immediately restore the primary Junos OS image using one of the following methods:

  • Install a new image using the CLI. When you install the new image, the new image is installed on only one partition–the alternate partition, meaning the router is now running two images. When you reboot, the router boots from the newly installed image, which becomes the primary image. So now there are two different images running on the router. Run the installation process again to update the other partition.
  • Use a snapshot of the backup root partition by entering the request system snapshot slice alternate command. After the primary root partition is recovered using this method, the device will successfully boot from the primary root partition on the next reboot. After the procedure, the primary root partition will contain the same version of Junos OS as the backup root partition.

    Note: You can use the CLI command request system snapshot slice alternate to back up the currently running root file system (primary or secondary) to the other root partition on the system.

    You can use this command to:

    • Save an image of the primary root partition in the backup root partition when the system boots from the primary root partition.
    • Save an image of the backup root partition in the primary root partition when the system boots from the backup root partition.

    Warning: The process of restoring the alternate root by using the CLI command request system snapshot slice alternate takes several minutes to complete. If you terminate the operation before completion, the alternate root might not have all required contents to function properly.

 

Related Documentation

 

Published: 2013-01-11

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