Backups should be performed on a regular schedule. You can use cron to automate this process and run backup tasks at specified times. Webmin's backup facility makes this very simple.
You can convert any filesystem backup task created in Webmin into an automatic backup. Start by creating a backup task as described in Creating a backup of a selected directory or Creating a backup of an entire mount point recipes of this chapter. Perform the following steps to set up automatic backups:
Navigate to System | Filesystem Backup.
Click a link in the Directory to backup column for the backup you would like to modify.
Open the Backup schedule section.
Set Scheduled backup enabled? to Enabled, at times chosen below.
Select Simple schedule and Weekly (on Sunday).