我正在用dockerfile在docker上构建mysql映像。我需要帮助，因为我有这个问题：身份验证插件'caching\u sha2\u password'无法加载
aman aggarwal的解决方案适合我，但我需要在自定义的my.cnf上编写它，我尝试用它重写my.cnf默认值，但在执行docker构建时出现错误：
复制失败：stat/var/lib/docker/tmp/docker-builder204357196/my.cnf:没有这样的文件或目录
这是我的自定义my.cnf：

# Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.

# 

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; version 2 of the License.

# 

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

# 

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA

# 

# The MySQL  Server configuration file.

# 

# For explanations see

# http://dev.mysql.com/doc/mysql/en/server-system-variables.html

[mysqld]
default_authentication_plugin = mysql_native_password
pid-file        = /var/run/mysqld/mysqld.pid
socket          = /var/run/mysqld/mysqld.sock
datadir         = /var/lib/mysql
secure-file-priv= NULL

# Disabling symbolic-links is recommended to prevent assorted security risks

symbolic-links=0

# Custom config should go here

!includedir /etc/mysql/conf.d/

这是我的文件：

# Indicates that the mysql image will be used as the base image.

FROM mysql

# Try copy my.cnf on this path /etc/mysql/

COPY my.cnf /etc/mysql/my.cnf

# Try only to restart mysql (not container)

RUN service mysql restart

我的文件夹结构：

proyectos(folder)
  ->build_docker
      ->Dockerfile
      ->my.cnf