按照http://ruby-china.org/topics/454mongodb数据库第一次很轻松的连上了，第二天却怎么也连接不上，然后在找到一个帖子说开启了没，安装，

suu@suu-virtual-machine:~$ ps aux | grep mongo
mongodb   5491  5.5  1.4 155304 29932 ?        Ssl  22:54   0:00 /usr/bin/mongod --config /etc/mongodb.conf
suu       5504  0.0  0.0   5684   800 pts/2    S+   22:54   0:00 grep --color=auto mongo

看来是开启了，

然后就这样确认 shell 下能不能连上：

suu@suu-virtual-machine:~$ mongo 127.0.0.1:27017
MongoDB shell version: 2.4.9
connecting to: 127.0.0.1:27017/test
Fri Feb 14 22:38:10.305 Error: couldn't connect to server 127.0.0.1:27017 at src/mongo/shell/mongo.js:147
exception: connect failed

还是不行，

在网上搜了好多，http://www.markpoor.com/connecting_mongodb_failed/说得清楚： 就是：电脑/服务器崩溃->非安全关闭，触发 mongodb 保护程序->系统自动在数据库根目录的 mongod.lock 文件上做记录->mongod.lock 非空，mongd 程序拒绝启动->无法连接数据库

因为我用的是虚拟机，加上用 redis，mysql 和 sql 的时候也没有关掉就关了虚拟机，所以习惯性直接关机 QAQ

处理方法： 删除数据库根目录下的 mongod.lock 文件里的东西就行了

然后重启虚拟机：sudo service mongodb start

suu@suu-virtual-machine:~$ mongo 127.0.0.1:27017
MongoDB shell version: 2.4.9
connecting to: 127.0.0.1:27017/test
Welcome to the MongoDB shell.
For interactive help, type "help".
For more comprehensive documentation, see
    http://docs.mongodb.org/
Questions? Try the support group
    http://groups.google.com/group/mongodb-user
Server has startup warnings: 
Fri Feb 14 22:54:11.748 [initandlisten] 
Fri Feb 14 22:54:11.748 [initandlisten] ** NOTE: This is a 32 bit MongoDB binary.
Fri Feb 14 22:54:11.748 [initandlisten] **       32 bit builds are limited to less than 2GB of data (or less with --journal).
Fri Feb 14 22:54:11.748 [initandlisten] **       Note that journaling defaults to off for 32 bit and is currently off.
Fri Feb 14 22:54:11.748 [initandlisten] **       See http://dochub.mongodb.org/core/32bit
Fri Feb 14 22:54:11.748 [initandlisten] 

搞了一天半，用了 n 种办法，没想到居然是这么简单的，记录下来，如果遇到类似问题的话就说不定可以节省掉不必要的麻烦了 QAQ，以我为鉴