This is a userAdmin vs. userAdminAnyDatabase question.
In the system.users I have the following users (password 1234 for both):
> db.system.users.find()
{ "_id" : ObjectId("52a976cb7851682aa44d6d4d"), "user" : "admin_one", "pwd" : "884f516cf308a4c6a75bbc5a0a00807b", "roles" : [ "userAdmin", "dbAdmin" ] }
{ "_id" : ObjectId("52a97c697851682aa44d6d4f"), "user" : "admin_two", "pwd" : "26e7bb644e5919461cd6ba7403dc6906", "roles" : [ "userAdminAnyDatabase", "dbAdminAnyDatabase" ] }
Connecting with a wrong user:
$ mongo mono -u admin -p 1234
connecting to: mono
Thu Dec 12 10:09:00.733 Error: 18 { code: 18, ok: 0.0, errmsg: "auth fails" } at src/mongo/shell/db.js:228
which is OK.
Connecting with the db admin:
$ mongo mono -u admin_one -p 1234
connecting to: mono
> db.system.users.find()
{ "_id" : ObjectId("52a976cb7851682aa44d6d4d"), "user" : "admin_one", "pwd" : "884f516cf308a4c6a75bbc5a0a00807b", "roles" : [ "userAdmin", "dbAdmin" ] }
{ "_id" : ObjectId("52a97c697851682aa44d6d4f"), "user" : "admin_two", "pwd" : "26e7bb644e5919461cd6ba7403dc6906", "roles" : [ "userAdminAnyDatabase", "dbAdminAnyDatabase" ] }
which is also OK.
Now, connecting with the "AnyDatabase" admin I get an error:
$ mongo mono -u admin_two -p 1234
connecting to: mono
> db.system.users.find()
error: { "$err" : "not authorized for query on mono.system.users", "code" : 16550 }
Why?