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[Upgrade EX switch] Stage 4 – Troubleshooting Upgrade Failure/Crash – System Stuck on Bootup



Article ID: KB20464 KB Last Updated: 09 Dec 2021Version: 7.0

This article documents Stage 4 – Troubleshooting Upgrade Failure/Crash. The EX device may get stuck in the boot process and fail to load the Junos OS. This article addresses the recovery methods.  

To go directly to other stages of upgrading Junos OS on EX switches, consult the Resolution Guide -- Upgrading EX Series.


  • The EX device is stuck loading Junos OS after upgrade.

  • How do I recover from a failed upgrade?

  • "Loading Junos" is reported in the LCD panel of the EX device.



Perform the following steps to recover from an upgrade failure on your EX switch:


  • If your EX device is a Virtual Chassis, then isolate the affected member and proceed as a stand-alone switch.

  • If your EX device has a Dual Routing Engine, fail over to the other Routing Engine, establish a console connection to the affected member, and proceed as detailed below.

  1. With a console connected to a stand-alone EX switch, which prompt or error is the bootup process stuck at? Click the prompt below to jump to the instructions.

Loader Prompt (Loader >)

  1. To recover the EX switch from the loader> prompt, reinstall the Junos software using one of the following methods:

  2. If a Root Cause Analysis is required after recovering, perform the steps in KB20569 - Collecting Logs from Juniper EX series Devices.

Debug Prompt (db>)

UBoot Prompt (=>)

  1. Type reset from the UBoot prompt, which will reboot the EX switch.

  2. Break the bootup sequence to get to the loader> prompt.

  3. When you see "Loading /boot/defaults/loader.conf" display, press Enter.

  4. Then press Enter to boot immediately, or press the Space bar for the command prompt.

  5. Press the Space bar to enter the manual loader. The loader > prompt displays.

(Note: There is a 1 second delay for pressing the Space bar. You can press the Space bar after you see "Loading /boot/defaults/loader.conf" message.)

  1. Perform the steps under "Loader Prompt" above.

Can't load kernel error

  1. Power cycle the EX device IF the console bootup process does not return to a prompt, and STOPS at the following display errors:

can't load '/kernel'
can't load '/kernel.old'
  1. If it continues to stop at the same errors after a reboot, and it does not progress to another prompt or process, then proceed to Step 2 in order to do a Format Install.

"Loading Junos" reported on LCD Panel

  1. If "Loading Junos" is constantly displayed on the LCD screen of the EX switch, connect a console to the EX switch. It is most likely that one of the prompts above will be displayed. If so, follow the instructions above. 

Sometimes when "Loading Junos" is reported, the Virtual Chassis must be reactivated with the request virtual-chassis reactivate command as follows:

--- JUNOS 10.0S10.1 built 2010-11-08 21:23:50 UTC
root@RE0:LC:1% cli
root@RE0:LC:1> request virtual-chassis reactivate

Note: The above command is applicable only if you see the switch on linecard mode; if you do not see this mode, proceed with the next step.

  1. If the above methods do not work, "Format Install" would be the last option to recover your device.

WARNING:  Performing a Format Install will format the entire file system & storage unit. Therefore, the EX switch will lose all configurations and logs. A Root Cause Analysis or recovery of any information from the EX switch will not be possible after a Format Install is performed. Do NOT perform this procedure if you need a Root Cause Analysis. Instead contact your technical support representative.

To perform Format Install on EX2200, EX3300, and EX4300 devices, proceed to KB20643 - [EX] Performing and resolving any common issues during Format Install on legacy EX platforms.

To perform Format Install on EX2300, EX3400, EX4400, EX4600, and EX4650 devices, proceed to KB31265 - [EX] How to format install EX2300s and EX3400s via USB.


Modification History:
  • 2020-02-13: Article reviewed for accuracy; minor, non-technical changes done

  • 2021-08-17: Added link for procedure on ELS devices that need to be formatted using USB

  • 2021-12-09: Updated KB to include current information and reference links


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