Old thread but I think I tried everything suggested by everyone here and on other forums and nothing worked. I can't stop hundreds of domains' backup by killing the processes one by one. This could take whole day.
So I simply:
1) Logged in to WHM panel and edited WHM backup configuration and selected 'disabled' and save.
2) Restarted server.
3) After reboot backup processes were gone and backup stopped. Easy way, isn't it
HitBiz.Net (HITBIZ INTERNATIONAL LLC, a registered US based business)
Domain Names and reliable (raid protected and with daily offsite backups and many more options) shared web hosting, reseller accounts and dedicated servers.
Safety & uptime of our customers' data is our main concern.