The mongodb configuration file is as follows:

[root@localhost ~]# cat /usr/local/mongodb/mongod.cnf 
bind_ip = 0.0.0.0
logpath=/data/mongodb/logs/mongodb.log
logappend = true
fork = true
#auth = true
port = 6068
dbpath=/data/mongodb/data
pidfilepath=/data/mongodb/mongod.pid

root super administrator privileges:
Close mongod.cnf profile parameter: auth
Log in to mongo directly and set the login password:

mongo --host 127.0.0.1 --port 6068
use admin
db.createUser({user: 'root', pwd:'TdLLQSdHgyn#6689', roles:[{role: 'root', db: 'admin'}]});
db.auth("root","TdLLQSdH689")

Close mongod
Open mongod.cnf profile parameter: auth =true

mongo --host 127.0.0.1 --port 6068
use admin
db.auth("root","TdLLQSdH689")

Create test library dbtest001, and test user testuser has read and write permission to dbtest001

use dbtest001
db.createUser({user:"testuser",pwd:"testuser123",roles:[{role:"readWrite",db:"dbtest001"}]})

//Create test user testuser with read permission to dbtest001 Library:
db.createUser({user:"testuser01",pwd:"testuser123",roles:[{role:"read",db:"dbtest001"}]})

Insert a collection (so-called table) into the test library:

db.chenji.insert({"name":"Floret","grade":"second grade","Gender":"male","hobby":"Study"})
WriteResult({ "nInserted" : 1 })
> db.chenji.insert({"name":"tearful","grade":"first grade","Gender":"female","hobby":"Sing"})
WriteResult({ "nInserted" : 1 })
> db.chenji.insert({"name":"Floret","grade":"Grade three","Gender":"female","hobby":"Play a ball"})
WriteResult({ "nInserted" : 1 })
> db.chenji.insert({"name":"Floret","grade":"fourth grade","Gender":"female","hobby":"draw"})
WriteResult({ "nInserted" : 1 })

To view users under the current library:

db.getUsers() perhaps show users

> show users
{
    "_id" : "dbtest001.testuser",
    "userId" : UUID("f275fad5-ac4f-4dfa-aea6-af34ed93c3e1"),
    "user" : "testuser",
    "db" : "dbtest001",
    "roles" : [
        {
            "role" : "readWrite",
            "db" : "dbtest001"
        }
    ]
}

To view the permissions of a user under the current library:

db.getUser("testuser")
db.getUser("testuser01")

Create role: db.createRole()
Update role: db.updateRole()
Delete role: db.dropRole()

Get a role information: db.getRole()

> db.getRole("read")
{
    "role" : "read",
    "db" : "dbtest001",
    "isBuiltin" : true,
    "roles" : [ ],
    "inheritedRoles" : [ ]
}
> db.getRole("readWrite")
{
    "role" : "readWrite",
    "db" : "dbtest001",
    "isBuiltin" : true,
    "roles" : [ ],
    "inheritedRoles" : [ ]
}

Delete all users: db.dropAllUsers()

Delete users: db.dropusers ("xxxxx")

db.dropUser("testuser01")
true

Assign a role to read and write to the user: db.grantRolesToUser()

use dbtest001
db.grantRolesToUser('testuser01',[ { role : 'readWrite', db : 'dbtest001' } ] )

Revoke a role permission of a user: db.revokeRolesFromUser()

> db.getUser("testuser01")
{
    "_id" : "dbtest001.testuser01",
    "userId" : UUID("d1fefe19-a94f-4300-8855-fd722f14e13f"),
    "user" : "testuser01",
    "db" : "dbtest001",
    "roles" : [
        {
            "role" : "readWrite",
            "db" : "dbtest001"
        }
    ]
}

Revoke read and write access to read role:

> db.revokeRolesFromUser('testuser01',[ { role : 'readWrite', db : 'dbtest001' }])
> db.getUser("testuser01")
{
    "_id" : "dbtest001.testuser01",
    "userId" : UUID("d1fefe19-a94f-4300-8855-fd722f14e13f"),
    "user" : "testuser01",
    "db" : "dbtest001",
    "roles" : [ ]
}

Change Password: db.changeUserPassword()

db.createUser({user:"testuser01",pwd:"testuser123",roles:[{role:"read",db:"dbtest001"}]})

Change Password:

> db.changeUserPassword("testuser01","123456")

Test: use the original password to log in and report an error as follows:

[root@localhost ~]# mongo 127.0.0.1:6068/dbtest001 -u testuser01 -p 'testuser123'
MongoDB shell version v3.6.16
connecting to: mongodb://127.0.0.1:6068/dbtest001?gssapiServiceName=mongodb
2020-01-01T21:51:35.637+0800 E QUERY    [thread1] Error: Authentication failed. :
connect@src/mongo/shell/mongo.js:263:13
@(connect):1:6
exception: connect failed

Login succeeded with new password

[root@localhost ~]# mongo 127.0.0.1:6068/dbtest001 -u testuser01 -p '123456'
MongoDB shell version v3.6.16
connecting to: mongodb://127.0.0.1:6068/dbtest001?gssapiServiceName=mongodb
Implicit session: session { "id" : UUID("966023f0-ff7b-4726-a216-8475bc729971") }
MongoDB server version: 3.6.16
> show collections;
chenji
> db.chenji.find();
{ "_id" : ObjectId("5e0c80a8efc383349153386a"), "name" : "Floret", "grade" : "second grade", "Gender" : "male", "hobby" : "Study" }
{ "_id" : ObjectId("5e0c80c3efc383349153386b"), "name" : "tearful", "grade" : "first grade", "Gender" : "female", "hobby" : "Sing" }
{ "_id" : ObjectId("5e0c83c8efc383349153386c"), "name" : "Floret", "grade" : "Grade three", "Gender" : "female", "hobby" : "Play a ball" }
{ "_id" : ObjectId("5e0c83e9efc383349153386d"), "name" : "Floret", "grade" : "fourth grade", "Gender" : "female", "hobby" : "draw" }

View the table under the current library:

show collections
chenji

To view everything in the collection:

> db.chenji.find();
{ "_id" : ObjectId("5e0c80a8efc383349153386a"), "name" : "Floret", "grade" : "second grade", "Gender" : "male", "hobby" : "Study" }
{ "_id" : ObjectId("5e0c80c3efc383349153386b"), "name" : "tearful", "grade" : "first grade", "Gender" : "female", "hobby" : "Sing" }

To view the record named Xiaohua:

> db.chenji.find({"name":"Floret"})
{ "_id" : ObjectId("5e0c80a8efc383349153386a"), "name" : "Floret", "grade" : "second grade", "Gender" : "male", "hobby" : "Study" }
{ "_id" : ObjectId("5e0c83c8efc383349153386c"), "name" : "Floret", "grade" : "Grade three", "Gender" : "female", "hobby" : "Play a ball" }
{ "_id" : ObjectId("5e0c83e9efc383349153386d"), "name" : "Floret", "grade" : "fourth grade", "Gender" : "female", "hobby" : "draw" }

reference material:
MongoDB user and role Interpretation Series (I)
http://www.mongoing.com/archives/26710

Summarize here first, and continue to learn and supplement later