Attempted to upgrade NFX, but it failed the 'show system storage' command when it was executed on JDM which showed the file system was in a normal state.

The following errors were generated on an attempt to upgrade NFX device:

root@jdm:/var/tmp# /usr/sbin/system-package-update update /var/tmp/jinstall-nfx-2-flex-15.1X53-D45.3.secure-domestic.tgz
System software upgrade in progress, please wait...
Pushing Junos image package to the host...
ERROR: The /var file system on the host is low on free disk space.
ERROR: This package requires 1503MB more space free. Please clean up /var on the host and retry.  
ERROR: Please use request app-engine cleanup command to delete old files from /var/tmp
Error: installation script exited with status 1
Error: Rolling back the staged upgrade!!
upgrade_platform: Requested rollback of a staged upgrade..
upgrade_platform: /boot/backup not found
Error: Installation failed, upgrade rolled back!!!

​Follow the instructions reported in the error:

ERROR: The /var file system on the host is low on free disk space.
ERROR: This package requires 1503MB more space free. Please clean up /var on the host and retry.  <----
ERROR: Please use request app-engine cleanup command to delete old files from /var/tmp
Error: installation script exited with status 1

Example:

1. Connect to the hypervisor from JDM shell:

   ​root@jdm:~# ssh hypervisor
   Last login: Fri Aug 17 23:52:26 2018 from jdm
   root@localhost:~#

2. Remove any large log file in the /var directory:

   root@localhost:~# rm LargeFile.txt

   Example command to find big files above 10M :

   sh -c 'find / -size +10485760c 2> /dev/null' | xargs du -h | sort -nr

​Once the log file is removed, the NFX will upgrade successfully.

2021-01-05: Added command for finding large files.