What is the best way to backup an entire opnsense machine (i.e. not just the configuration files but the entire box)?
Boot Linux and dd the full drive. Can be easily done with clonezilla (local boot media, manually ) or fog (network boot, automatically).
However copying the config.xml + voucher db + maybe rrd data and logs should be more than sufficient.
Thank you, I know virtually nothing about the Linux environment, but you've given me some keywords to google so hopefully, that will be all I need to get going!
If you have a ZFS install take a look at the nifty zfs-send and zfs-receive utilities.
Cheers,
Franco