Description

The unable to load kernel issue can be seen on Junos devices due to a mismatch in the free BSD version and Junos version, corrupted software package or actual hardware issue.  The image installation will not be complete and the device will be in a boot loop. 

A kernel is a fundamental component of an operating system (OS). It acts as a bridge between software applications and the hardware of a computer system. The kernel is responsible for managing system resources such as CPU, memory, disk, and input/output devices

 

Symptoms

The below error will be thrown when there is issue with kernel. 
  
Choice:
Booting from Junos volume ...
/
Unable to load a kernel!
Error while including /boot/loader.rc, in the line:
junos-start
/
can't load 'kernel'

 

Solution

The unable the load a kernel issue will occur when there is an underlying issue with the software. The reasons include a mismatch between Free BSD and Junos, a corrupted OS package or an actual underlying issue. 

Junos leverages the FreeBSD kernel and enhances it with additional networking features and functionalities specific to Juniper's networking hardware.

The Free BSD version for the range of Junos versions varies, for example, the Free BSD version for Junos OS 17.XX and Older is 10 and for 18.XX and later is 11. When a customer tries to load the Junos software on the older FreeBSD version the Kernel will throw an error while booting the image. 

To check the version of FreeBSD and its build on Junos device, you can use the following command.
 

labroot@android-re0> start shell
% uname -mrs
FreeBSD JNPR-11.0-20230406.a7d7ea1_buil amd64


The above indicates FreeBSD for Juniper Junos is 11.0

It is necessary to follow the FreeBSD upgrade before Junos upgrade if the Junos upgrade is a step-up upgrade. For example, if Junos upgrades 15.XX will have FreeBSD versions 10 and from 15.XX Junos, 18.XX Junos upgrade is being performed, upgrading the FreeBSD is advised. 


For more information on how to upgrade FreeBSD, you can check this Knowledge Base

Even after the FreeBSD upgrade,  if Kernel is unable to load- try recovering the Junos by using the boot loader prompt for various boot options- boot from Junos, boot from recovery volume. Follow this Documentation Link for recovery of the Junos device.

If the issue persists, open a JTAC case, an RMA for the device ( routing engine) may be required.

Modification History

2024-05-25 : Article Created