This file does not exist by default. You may create the file if you want to change the directory used by Shorewall to store state information, including compiled firewall scripts. By default, the directory used is /var/lib/shorewall/ for IPv4 and /var/lib/shorewall6/ for IPv6
The file contains a single variable assignment:
where directory is the name of a directory. If you add this file, you should copy the files from /var/lib/shorewall to the new directory before performing a shorewall restart.
The man page shorewall6-vardir(5) is an alias of shorewall-vardir(5).