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[EX] While booting up, switch stuck in db> mode



Article ID: KB20635 KB Last Updated: 13 Sep 2021Version: 4.0

When an EX switch is stuck at db> prompt, capturing information will help in understanding the reason the EX switch crashed and help determine a root cause. This article explains how information can be captured for troubleshooting purposes.



While booting up an EX switch, it is stuck at db> prompt. How do I recover? What data should I collect if I need a Root Cause Analysis?



Perform the following steps:

  1. First, collect the following command outputs from the db> mode / prompt:

db> x/s version     
db> alltrace
db> ps
db> show allvms
db> show msgbuf
db> show registers
db> show lock
db> show uma
  1. After the information in Step 1 is collected, enter cont to continue:

db> cont

Do you get the CLI prompt?

  • No - Continue with Step 3.

  • Yes - Jump to Step 4.

  1. Reboot, and try and recover from loader mode (loader>). If you do NOT get a loader> prompt, open a case with your technical support representative.

To recover the EX switch from the loader> prompt, reinstall the Junos OS software by performing a Format Install. If a Root Cause Analysis is required after recovery, perform the steps in KB20569 - [EX/QFX] How to collect logs and files from standalone and Virtual Chassis/VCF devices.

  1. At the CLI prompt, check to see if there are any core files on the switch with the command show system core-dumps. If there are core dumps, their location will be shown with the aforementioned command. You can copy them to a server by using FTP for further analysis.


Modification History:
  • 2020-02-17: Article reviewed for accuracy; no changes required.

  • 2021-09-13: Article reviewed and summarized, redundant links removed. In case of core-dumps, users no longer need to go to shell to find them.


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