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[EX] Recovering from the "not a JUNOS snapshot" error



Article ID: KB32880 KB Last Updated: 03 Apr 2019Version: 1.0

When there are bad blocks, users may encounter the /dev/da0s1a is not a JUNOS snapshot error on EX Series switches.

This article explains how to recover the switch or virtual chassis from the error.



The output of show system snapshot media internal says /dev/da0s1a is not a JUNOS snapshot.

labroot@jtac> show system snapshot media internal
error: /dev/da0s1a is not a JUNOS snapshot

error: /dev/da0s1a is not a JUNOS snapshot



This might be because the /var/tmp directory is full or at more than 82% storage due to which the image cannot be uncompressed or because there has been an ungraceful shutdown, which has led to corruption of partitions or flash corruption.



To check for any file system corruption, perform the following:

  1. Log in as root user to the shell.
> start shell user root
  1. Check if any bad blocks exist currently on the primary .

% nand-mediack –C  

If there are any bad blocks, a sequence of output will be generated.

  1. To clear the bad blocks, execute the following:
% nand-mediack     
% fsck –f
  1. Check again if any bad blocks exist.

% nand-mediack –C

For more information, see KB20570 - [EX/SRX] Recovering from file system corruption during a system reboot, NAND media utility checks for bad blocks in the NAND flash memory.

Note: After step 4, if the bad blocks still exist, perform the previous steps a few more times to clear the bad blocks. If they continue to exist, it could be a faulty hardware and there may be a need to replace it. Contact Support in this case.


If there are no more bad blocks, continue to the following steps:

  1. Copy the required image to the primary and perform the following steps to write a proper Junos OS snapshot.
request system software add <filepath> member <memberid> reboot
  1. After the primary comes up, execute the show version command, verify the output, and then proceed to create a snapshot as follows:

request system snapshot slice alternate

labroot@jtac > show system snapshot media internal
Information for snapshot on       internal (/dev/da0s1a) (primary)
Creation date: Jan 14 00:33:17 2019
JUNOS version on snapshot:
  jdocs-ex: 14.1X53-D40.8
  junos  : ex-14.1X53-D40.8
  junos-ex-4300: 14.1X53-D40.8
  jweb-ex: 14.1X53-D40.8
Information for snapshot on       internal (/dev/da0s2a) (backup)
Creation date: Jan 13 19:32:09 2019
JUNOS version on snapshot:
  jdocs-ex: 14.1X53-D47.6
  junos  : ex-14.1X53-D47.6
  junos-ex-4300: 14.1X53-D47.6
  jweb-ex: 14.1X53-D47.6
  1. In case there is an issue with the primary booting up, we will have to perform a format installation through a USB.

    1. We need to first format the USB with the FAT32 file system. Copy only the Junos OS release 12.3 image to the USB. Interrupt the boot-sequence by using the spacebar to get into loader prompt: loader>
    2. Execute the following command:  

      install file:///jinstall-ex-version-domestic-signed.tgz

    3. Execute the show version command to verify the installation:

labroot@jtac> show version
Hostname: jtac-EX4300-24T-r010
Model: ex4300-24t
Junos: 14.1X53-D40.8
JUNOS EX  Software Suite [14.1X53-D40.8]
JUNOS FIPS mode utilities [14.1X53-D40.8]
JUNOS Online Documentation [14.1X53-D40.8]
JUNOS EX 4300 Software Suite [14.1X53-D40.8]
JUNOS Web Management Platform Package [14.1X53-D40.8]
JUNOS py-base-powerpc [14.1X53-D40.8]

For more information, see KB20643 - [EX Switch] Rewrite the entire file system by issuing "install --format" command from "Loader" mode (Format Install).


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