If set, the command or script entered will be run as `root` before the backup is run on schedule. This can be useful for mounting removable or remote filesystems to which the backup should be written.

If the command fails (with a non-zero exit status), the rest of the backup will not proceed.

The command can discover information about the backup via environment variables starting with `BACKUP_` , like:

`BACKUP_DOMAIN_NAMES`
  Names of all the virtual servers being backed up.

`BACKUP_DEST`
  The destination directory or URL.

`BACKUP_FEATURES`
  Names of all Virtualmin features included in the backup. If `BACKUP_ALL` is set to 1, all features are included.