Why my backgroundrb always interrupted


I have a ror site,when I run a backgroud job which implemented by BackgrounDRB,but I found the job always interrupted by system,sometime it interrupted in 2 minute after it started,sometime in half an hour or more.But it never
exceed 2 hours.I checked my cpu time,it’s low.
I really don’t know what has happend.someone can help me?




thank you