It is necessary to install Unison on your PC; unfortunately, that is outside the remit of this wiki.
Once installed, to activate a backup manually, you need to issue a unison command from your PC (referred to as the client in Unison)
To synchronise backup:
unison filename ssh://192.168.1.250/ShareName/filename
Note, if your user was created in FreeNAS with the home directory as /mnt (default setting, as advised), then /mnt should not be included in the ssh path above.
This only works for files synchronised from FreeNAS to PC due to permissons (chmod) errors when synchronising from PC to FreeNAS. If this error occurs for you, it is likely the file you are synchronising exists in a folder with root ownership (don't worry if you don't understand what that means). To rectify this, just use unison with root ssh:
unison filename ssh://email@example.com//mnt/ShareName/filename
Note, the double / in the ssh path for root here.
To synchronise whole directories, just replace filename with directory_name (examples below):
unison directory_name ssh://firstname.lastname@example.org//mnt/ShareName/directory_name unison /path_to/directory_name ssh://email@example.com//mnt/ShareName/path_to/directory_name
These commands just need to be run on the Unison client at regular intervals to ensure all copies of files within the selected directories are kept up-to-date with changes. It is possible to schedule regular backups from each networked PC if you know how to schedule events on your PC.
NB: ShareName is the HD mount point given when formatting the drive.