Modern distributed systems are designed to tolerate node crashes. However, incorrect crash recovery mechanisms and implementations can still introduce crash recovery bugs, and hurt reliability and availability of cloud systems. In this paper, we present Deminer, a novel crash injection technique that automatically injects node crashes/reboots to effectively expose crash recovery bugs in cloud systems. We observe that, node crashes that interrupt the execution of related operations, which store common data to different places (i.e., different storage paths or nodes), are more likely to trigger crash recovery bugs. Based on this observation, Deminer first tracks the critical data usage in a correct run. Then Deminer identifies related operations and predicts error-prone crash points. Finally, Deminer tests the predicted crash points and checks whether the target system can behave correctly. We have evaluated Deminer on three widely-used cloud systems: ZooKeeper, HBase and HDFS. Deminer has detected 6 crash recovery bugs. A video demonstration of Deminer is available at https://youtu.be/7wWqXlpSjiM.