问题：
在docker中启动mysql容器，在mysql容器中对数据库的更改（如创建数据库，更改数据等），在commit后再次进入容器发现之前的更改全部没有保存，如：
步骤如下：
1.后台运行mysql容器，设置容器名称为mysql：
[root@localhost ~]# docker run --name=mysql -p 3306:3306 -d owenchen1992/mysql
f80791a0daf194fdba94f16a9d89ebec8ba8fbd8af28d3ea8b599b9d705f85ba
2.进入容器bash和mysql，创建一个数据库TEST_DB,并验证TEST_DB创建成功:
[root@localhost ~]# docker exec -it mysql bash
root@f80791a0daf1:/# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.20 MySQL Community Server (GPL)
Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
4 rows in set (0.00 sec)
mysql> create database TEST_DB;
Query OK, 1 row affected (0.01 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| TEST_DB |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
3.退出容器，并commit更改到镜像：
mysql> exit
Bye
root@f80791a0daf1:/# exit
exit
[root@localhost ~]# docker commit mysql owenchen1992/mysql
sha256:8beaeefdd1c3d23981f5d2d69089f998ae1dbfec0e023005df07031477011fe6
4.重新启动容器并进入bash和mysql，发现之前创建的TEST_DB不见了，说明之前的更改无效：
[root@localhost ~]# docker container stop mysql
mysql
[root@localhost ~]# docker container rm mysql
mysql
[root@localhost ~]# docker run --name=mysql -p 3306:3306 -d owenchen1992/mysql
a1a1b4174caaadda0ec4b01b9fe5f92d6b3464d85284042274f71aebde0915dd
[root@localhost ~]# docker exec -it mysql bash
root@a1a1b4174caa:/# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.20 MySQL Community Server (GPL)
Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
4 rows in set (0.00 sec)
问题原因：
在mysql的Dockerfile中有这样一行:
VOLUME /var/lib/mysql
这意味在容器中的目录/var/lib/mysql的所有修改会对应到宿主机的某个位置，可以通过命令查看具体对应的宿主机目录：docker inspect containerID/name. 当运行docker commit时，容器中的/var/lib/mysql目录的更改并不会提交到镜像中，但这些更改是随时与宿主机对应的目录同步的。当重新启动commit后的镜像时，container会重新在宿主机中创建一个目录来保存其数据更新，因此并不是原先的宿主机目录，所以新开启的容器看不到之前的数据更改。
解决方法：
我们已经知道了问题发生的原因，就不难解决这个问题了，步骤如下：
1.找到mysql容器对应的宿主机目录"/var/lib/docker/volumes/8496bbf33782bdadc027cdcf23197e5ebc36d11deb69ee833d63b557b3a7183d/_data"：
[root@localhost ~]# docker inspect mysql
[
......
"Source": "/var/lib/docker/volumes/8496bbf33782bdadc027cdcf23197e5ebc36d11deb69ee833d63b557b3a7183d/_data",
"Destination": "/var/lib/mysql",
......
]
2.在mysql中创建一个数据库TEST_DB:
[root@localhost ~]# docker exec -it mysql bash
root@a1a1b4174caa:/# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.7.20 MySQL Community Server (GPL)
Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> create database TEST_DB;
Query OK, 1 row affected (0.00 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| TEST_DB |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
mysql>
3.退出容器，停止容器，删除容器（不需要docker commit更新镜像）：
mysql> exit
Bye
root@a1a1b4174caa:/# exit
exit
[root@localhost ~]# docker container stop mysql
mysql
[root@localhost ~]# docker container rm mysql
mysql
4.后台运行容器，并将宿主机对应的目录挂载到容器的/var/lib/mysql目录下并开启读写权限（关键步骤）：
[root@localhost ~]# docker run --name=mysql -p 3306:3306 -v /var/lib/docker/volumes/8496bbf33782bdadc027cdcf23197e5ebc36d11deb69ee833d63b557b3a7183d/_data:/var/lib/mysql:rw -d owenchen1992/mysql
5.此时进入新开启的容器，并查看数据库：
[root@localhost ~]# docker exec -it mysql bash
root@c7a9c8415654:/# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.20 MySQL Community Server (GPL)
Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| TEST_DB |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
mysql>
6.发现刚才创建的数据库TEST_DB没有因为重新运行容器而消失，问题解决！