[root@VM-20-8-centos init.d]# service mongodb_27018 start
about to fork child process, waiting until server is ready for connections.
forked process: 29002
ERROR: child process failed, exited with 100
To see additional information in this output, start without the "--fork" option.

查看mongodb的日志

tail -50f   mongodb的log目录/config.log

// 日志内容是否有出现下面两个中的一个者使用下面的解决方案
Requested option conflicts with current storage engine option for directoryPerDB; you requested true but the current server storage is already set to false and cannot be changed 

 An incomplete repair has been detected! This is likely because a repair operation unexpectedly failed before completing. MongoDB will not start up again without --repair

 
 
解决方案

//删除db目录里面的/mongod.lock ，否则下面的命令是运行不成功的
rm -rf db目录//mongod.lock

//修复数据
mongod --dbpath db目录 --repair

//删除db目录里面的storage.bson 
rm -rf db目录/storage.bson

//然后用root用户进行启动
sudo -u root mongod -f 配置文件路径