1. 最開始的時候，我們啟動mongodb，但是不包含--auth引數：

E:\MongoDB\bin>mongod --dbpath=E:\mongodb\db
Thu Jul 04 16:31:58.700 [initandlisten] db version v2.4.4
Thu Jul 04 16:31:58.700 [initandlisten] git version: 4ec1fb96702c9d4c57b1e06dd34eb73a16e407d2
Thu Jul 04 16:31:58.700 [initandlisten] build info: windows sys.getwindowsversion(major=6, minor=0, build=6002, platform=2, servic
e_pack='Service Pack 2') BOOST_LIB_VERSION=1_49
Thu Jul 04 16:31:58.700 [initandlisten] allocator: system
Thu Jul 04 16:31:58.700 [initandlisten] options: { dbpath: "E:\mongodb\db" }
Thu Jul 04 16:31:58.731 [initandlisten]
Thu Jul 04 16:31:58.731 [initandlisten] ** WARNING: mongod started without --replSet yet 1 documents are present in local.system.r
eplset
Thu Jul 04 16:31:58.731 [initandlisten] **          Restart with --replSet unless you are doing maintenance and no other clients a
re connected.
Thu Jul 04 16:31:58.731 [initandlisten] **          The TTL collection monitor will not start because of this.
Thu Jul 04 16:31:58.731 [initandlisten] **          For more info see http://dochub.mongodb.org/core/ttlcollections
Thu Jul 04 16:31:58.731 [initandlisten]
Thu Jul 04 16:31:58.981 [initandlisten] waiting for connections on port 27017
Thu Jul 04 16:31:58.981 [websvr] admin web console waiting for connections on port 28017
 

另開一Dos視窗，直接連線到test資料庫上：

E:\MongoDB\bin>mongo
MongoDB shell version: 2.4.4
connecting to: test

2. 連線到admin資料庫，在admin資料庫上建立一個使用者，這個使用者儲存在admin.system.users中，它的許可權比在其它資料庫中設定的使用者許可權更大。（當admin.system.users中一個使用者都沒有時，即使mongod啟動時添加了--auth引數，如果沒有在admin資料庫中新增使用者，此時不進行任何認證還是可以做任何操作，直到在admin.system.users中添加了一個使用者。）

> use admin
switched to db admin
> db.system.users.find()
> db.addUser("allenlei","123456")
{
        "user" : "allenlei",
        "readOnly" : false,
        "pwd" : "a9eadc99bab4734b32f5bc4148d866c6",
        "_id" : ObjectId("51d534878704a2ac963ed790")
}
> db.system.users.find()
{ "_id" : ObjectId("51d534878704a2ac963ed790"), "user" : "allenlei", "readOnly" : false, "pwd" : "a9eadc99bab4734b32f5bc4148d866c6
" }
>
 

3. 現在admin資料庫中已經有使用者資訊了，我們關掉mongodb, 重新啟動，這次帶有--auth 引數。

E:\MongoDB\bin>mongod --dbpath=E:\mongodb\db --auth
Thu Jul 04 16:44:57.393 [initandlisten] db version v2.4.4
Thu Jul 04 16:44:57.393 [initandlisten] git version: 4ec1fb96702c9d4c57b1e06dd34eb73a16e407d2
Thu Jul 04 16:44:57.409 [initandlisten] build info: windows sys.getwindowsversion(major=6, minor=0, build=6002, platform=2, servic
e_pack='Service Pack 2') BOOST_LIB_VERSION=1_49
Thu Jul 04 16:44:57.409 [initandlisten] allocator: system
Thu Jul 04 16:44:57.409 [initandlisten] options: { auth: true, dbpath: "E:\mongodb\db" }
Thu Jul 04 16:44:57.440 [initandlisten]
Thu Jul 04 16:44:57.440 [initandlisten] ** WARNING: mongod started without --replSet yet 1 documents are present in local.system.r
eplset
Thu Jul 04 16:44:57.440 [initandlisten] **          Restart with --replSet unless you are doing maintenance and no other clients a
re connected.
Thu Jul 04 16:44:57.440 [initandlisten] **          The TTL collection monitor will not start because of this.
Thu Jul 04 16:44:57.440 [initandlisten] **          For more info see http://dochub.mongodb.org/core/ttlcollections
Thu Jul 04 16:44:57.440 [initandlisten]
Thu Jul 04 16:44:57.549 [websvr] admin web console waiting for connections on port 28017
Thu Jul 04 16:44:57.549 [initandlisten] waiting for connections on port 27017

4. 由於指定了-auth引數，那麼連線到資料庫上就需要提供登入賬戶，儘管不提供也可以登入到test這個預設資料庫，但是沒辦法操作：

E:\MongoDB\bin>mongo
MongoDB shell version: 2.4.4
connecting to: test
> show collections
Thu Jul 04 16:53:51.752 JavaScript execution failed: error: {
        "$err" : "not authorized for query on test.system.namespaces",
        "code" : 16550
} at src/mongo/shell/query.js:L128
>

5. 現在我們指定連線到admin資料庫，如果賬戶不對：

E:\MongoDB\bin>mongo --authenticationDatabase admin -u allenlei -p
MongoDB shell version: 2.4.4
Enter password:
connecting to: test
Thu Jul 04 16:56:55.569 JavaScript execution failed: Error: 18 { code: 18, ok: 0.0, errmsg: "auth fails" } at src/mongo/shell/db.j
s:L228
exception: login failed

6. 奇怪的是，就算是賬戶正確，我的機器上也是顯示連線到test資料庫而不是admin。我需要轉到admin資料庫上，（root是建立在test資料庫上的賬戶）

E:\MongoDB\bin>mongo --authenticationDatabase admin -u allenlei -p
MongoDB shell version: 2.4.4
Enter password:
connecting to: test
> db.system.users.find()
{ "_id" : ObjectId("51d3e1c94ef3aba14566b889"), "user" : "root", "readOnly" : false, "pwd" : "b3098ef4591719e9f75972a75883726b" }
> use admin
switched to db admin
> db.system.users.find()
{ "_id" : ObjectId("51d5378a6a7de1fde965535c"), "user" : "allenlei", "readOnly" : false, "pwd" : "a9eadc99bab4734b32f5bc4148d866c6
" }
>
> show collections
system.indexes
system.users
> use tutorial
switched to db tutorial
> show collections
newCollection_noCapped
numbers
person
personalinfo
photo.chunks
photo.files
student
student_res
system.indexes
system.users
users
>

可以看出，通過admin資料庫登入，可以以登入賬戶進入其他資料庫進行操作。

7. 現在用root賬號登入test資料庫：

E:\MongoDB\bin>mongo -authenticationDatabase test -u root -p
MongoDB shell version: 2.4.4
Enter password:
connecting to: test
> show collections
person
system.indexes
system.users
> db.system.users.find()
{ "_id" : ObjectId("51d53a706ce04d74431706b4"), "user" : "root", "readOnly" : false, "pwd" : "34e5772aa66b703a319641d42a47d696" }
> use tutorial
switched to db tutorial
> show collections
Thu Jul 04 17:04:51.186 JavaScript execution failed: error: {
        "$err" : "not authorized for query on tutorial.system.namespaces",
        "code" : 16550
} at src/mongo/shell/query.js:L128
>

root賬戶屬於test而不是admin資料庫，許可權只能在本資料庫使用，而不像allenlei可以到tutorial資料庫操作。