"No space left on device" error observed, when trying to download Junos Install file to "/var/tmp" folder as a part of Junos Upgrade. Running "request system storage cleanup" did not helped in resolving the issue 

Below error logs and "show system storage" was reporting 100% usage of "/var" partition 

labuser@labhost> file copy http://download.juniper.com/files/tftp/firmware/juniper/legacy/jinstall-ppc-14.2X9.1-domestic-signed.tgz /var/tmp/

/var: write failed, filesystem is full

error: error making temporary directory (/var/home/labuser/...transferring.file.........AHAMZl): No space left on device

There were some huge files saved in customer home directory and was not deleted when we ran "request system storage cleanup" command. Used below "find" command to serach and list huge file in the "/" (root) file system. We deleted unwanted huge files from user home directory to save disk space

labuser@labhost> start shell user root 

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