在mac上，Mongodb服務啟動：
命令：
mongod -f /usr/local/mongodb/mongod.conf
mongod.conf中設置內容：
dbpath=/usr/local/mongodb/data/db
logpath=/usr/local/mongodb/data/log/mongodb.log
pidfilepath=/usr/local/mongodb/log/master.pid?
directoryperdb=true?
logappend=true?
bind_ip=127.0.0.1
port=27017?
fork=true?
