service crond restart 

crontab 堵塞会挂掉
检查日志

tail -fn 500 /var/log/cron

出现错误信息如下：

Apr 22 13:35:01 elcndc2zhjz13 crond[84354]: (root) FAILED to authorize user with PAM (Module is unknown)
Apr 22 13:40:01 elcndc2zhjz13 crond[84542]: (root) FAILED to authorize user with PAM (Module is unknown)
Apr 22 13:40:01 elcndc2zhjz13 crond[84543]: (root) FAILED to authorize user with PAM (Module is unknown)
Apr 22 13:40:01 elcndc2zhjz13 crond[84544]: (root) FAILED to authorize user with PAM (Module is unknown)
Apr 22 13:45:01 elcndc2zhjz13 crond[84731]: (root) FAILED to authorize user with PAM (Module is unknown)
Apr 22 13:50:01 elcndc2zhjz13 crond[84919]: (root) FAILED to authorize user with PAM (Module is unknown)
Apr 22 13:50:01 elcndc2zhjz13 crond[84920]: (root) FAILED to authorize user with PAM (Module is unknown)
Apr 22 13:50:01 elcndc2zhjz13 crond[84921]: (root) FAILED to authorize user with PAM (Module is unknown)
Apr 22 13:55:01 elcndc2zhjz13 crond[85110]: (root) FAILED to authorize user with PAM (Module is unknown)
Apr 22 14:00:01 elcndc2zhjz13 crond[85298]: (root) FAILED to authorize user with PAM (Module is unknown)
Apr 22 14:00:01 elcndc2zhjz13 crond[85297]: (root) FAILED to authorize user with PAM (Module is unknown)
Apr 22 14:00:01 elcndc2zhjz13 crond[85299]: (root) FAILED to authorize user with PAM (Module is unknown)
Apr 22 14:01:01 elcndc2zhjz13 crond[85335]: (root) FAILED to authorize user with PAM (Module is unknown)