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Understanding System Snapshot on an ACX Series Router


The system snapshot feature enables you to create copies of the software running on an ACX Series router. You can use the system snapshot feature to take a “snapshot” of the files currently used to run the router—the complete contents of the root (/) and /config directories, which include the running Juniper Networks Juniper operating system (Junos OS) and the active configuration—and copy all of these files to another media, such as a universal serial bus (USB) storage device, the active slice of a dual-root partitioned router, or the alternate slice of a dual-root partitioned router.


Junos OS automatically uses the backup software if the currently running software goes bad. For example, if the da0s1 slice goes bad, Junos OS automatically comes up using the da0s2 slice, and takes a snapshot of the da0s2 slice and copies it to the da0s1 slice if the auto snapshot functionality is configured, which is disabled by default. However, you can also do this manually using the system snapshot feature.


In ACX5048 and ACX5096 routers, the system snapshot feature is applicable only when a USB storage device is used.

Typically, you can take a snapshot prior to the upgrade of an image on the dual internal NAND flash device (da0s1 or da0s2), or to remedy a bad image, thereby preventing the bad image from rendering the system useless. A snapshot to another media ensures that the device can boot from the other media in case the system does not boot up from the current image.

You can take a snapshot of the currently running software and configuration on a router in the following situations:

  • The router's active slice (for example, da0s1) is updated with a new Junos OS image (using the jinstall package). In such a case, you must update the other slice (da0s2) with the new image.


    The active slice can be da0s1 or da0s2.

  • The router's active slice (for example, da0s1) is corrupted and the router is rebooted from the backup slice (that is, from da0s2). Therefore, you must restore a new image on the active slice—that is, on da0s1.

  • Both slices of the router's dual internal NAND flash device are corrupted and the router continues trying to reboot. In this situation, you can insert a USB storage device, boot the router from that device, and restore the NAND flash device slices—da0s1 and da0s2.


    Before you attempt to take a snapshot from the USB storage device, ensure that the USB storage device contains an image of Junos OS from which the router can boot up.