Docker DELETE命令每半小时执行一次

我是新来的docker工人，正在通过docker日志，发现DELETE命令每半小时执行一次

time="2017-10-09T09:36:39.757830525Z" level=error msg="Handler for DELETE /v1.17/images/sha256:69522f5b2cfaf11703b4911fe40c2dc8e1f1469ab756910f0cf679e2b1db1960 returned error: conflict: unable to delete 69522f5b2cfa (must be forced) - image is being used by stopped container f7142fd07c44" time="2017-10-09T10:06:39.758068930Z" level=error msg="Handler for DELETE /v1.17/images/sha256:69522f5b2cfaf11703b4911fe40c2dc8e1f1469ab756910f0cf679e2b1db1960 returned error: conflict: unable to delete 69522f5b2cfa (must be forced) - image is being used by stopped container f7142fd07c44" time="2017-10-09T10:36:39.757730005Z" level=error msg="Handler for DELETE /v1.17/images/sha256:69522f5b2cfaf11703b4911fe40c2dc8e1f1469ab756910f0cf679e2b1db1960 returned error: conflict: unable to delete 69522f5b2cfa (must be forced) - image is being used by stopped container f7142fd07c44" time="2017-10-09T11:06:39.757938287Z" level=error msg="Handler for DELETE /v1.17/images/sha256:69522f5b2cfaf11703b4911fe40c2dc8e1f1469ab756910f0cf679e2b1db1960 returned error: conflict: unable to delete 69522f5b2cfa (must be forced) - image is being used by stopped container f7142fd07c44" 

任何想法为什么DELETE命令正在重复执行？ 我如何debugging？