我正在使用 Symfony 4，Mysql 版本是 8.0.11，并且使用用户而不是 root 登录，当我尝试使用该命令时php bin/console make:migration出现此错误：
In AbstractMySQLDriver.php line 126:
An exception occurred in driver: SQLSTATE[HY000] [2006] MySQL server has gone away
In PDOConnection.php line 50:
SQLSTATE[HY000] [2006] MySQL server has gone away
In PDOConnection.php line 46:
SQLSTATE[HY000] [2006] MySQL server has gone away
In PDOConnection.php line 46:
PDO::__construct(): Unexpected server respose while doing caching_sha2 auth: 109
然后我尝试在线搜索，发现 MySQL 变量出了问题wait_timeout，max_allowed_packet必须更改文件中的这些变量/etc/mysql/my.cnf，问题是当我去编辑该文件时我只发现这个：
# Copyright (c) 2015, 2016, 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, version 2.0,
# as published by the Free Software Foundation.
#
# This program is also distributed with certain software (including
# but not limited to OpenSSL) that is licensed under separate terms,
# as designated in a particular file or component or in included license
# documentation. The authors of MySQL hereby grant you an additional
# permission to link the program and your derivative works with the
# separately licensed software that they have included with MySQL.
#
# 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, version 2.0, 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
# * IMPORTANT: Additional settings that can override those from this file!
# The files must end with '.cnf', otherwise they'll be ignored.
!includedir /etc/mysql/conf.d/
!includedir /etc/mysql/mysql.conf.d/
然后我尝试查看一个名为“为什么 /etc/mysql/my.cnf 是空的？“并且有用户说使用以下其中一条路径：
/etc/mysql/conf.d/
/etc/mysql/mysql.conf.d/
/etc/mysql/mysql.conf.d/mysqld.cnf
所以我尝试了...
/etc/mysql/conf.d/：
## Copyright (c) 2015, 2016, 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, version 2.0,
# as published by the Free Software Foundation.
#
# This program is also distributed with certain software (including
# but not limited to OpenSSL) that is licensed under separate terms,
# as designated in a particular file or component or in included license
# documentation. The authors of MySQL hereby grant you an additional
# permission to link the program and your derivative works with the
# separately licensed software that they have included with MySQL.
#
# 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, version 2.0, 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 Client configuration file.
#
# For explanations see
# http://dev.mysql.com/doc/mysql/en/server-system-variables.html
[mysql]
在文件中/etc/mysql/mysql.conf.d/：
# Copyright (c) 2014, 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, version 2.0,
# as published by the Free Software Foundation.
#
# This program is also distributed with certain software (including
# but not limited to OpenSSL) that is licensed under separate terms,
# as designated in a particular file or component or in included license
# documentation. The authors of MySQL hereby grant you an additional
# permission to link the program and your derivative works with the
# separately licensed software that they have included with MySQL.
#
# 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, version 2.0, 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]
pid-file = /var/run/mysqld/mysqld.pid
socket = /var/run/mysqld/mysqld.sock
datadir = /var/lib/mysql
log-error = /var/log/mysql/error.log
并在文件中/etc/mysql/mysql.conf.d/mysqld.cnf：
# Copyright (c) 2014, 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, version 2.0,
# as published by the Free Software Foundation.
#
# This program is also distributed with certain software (including
# but not limited to OpenSSL) that is licensed under separate terms,
# as designated in a particular file or component or in included license
# documentation. The authors of MySQL hereby grant you an additional
# permission to link the program and your derivative works with the
# separately licensed software that they have included with MySQL.
#
# 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, version 2.0, 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]
pid-file = /var/run/mysqld/mysqld.pid
socket = /var/run/mysqld/mysqld.sock
datadir = /var/lib/mysql
log-error = /var/log/mysql/error.log
并且在任何这些文件中我都找不到 MySQL 变量wait_timeout和max_allowed_packet，所以如果有人能帮助我解决这个问题，我提前谢谢了。:)
PS：（php bin/console make:migration在出现此错误之前我已经运行过此命令几次，并且创建了数据库，并且运行正常，所以这似乎不是安装问题）。
更新：似乎成功地改变了两个变量wait_timeout，并max_allowed_packet通过在三个文件中添加以下内容来全局改变
max_allowed_packet=1024M
wait_timeout=3000000
然后使用此命令sudo service mysql restart
给我这个：
mysql> SHOW global VARIABLES LIKE "wait_timeout";
+---------------+---------+
| Variable_name | Value |
+---------------+---------+
| wait_timeout | 3000000 |
+---------------+---------+
1 row in set (0,00 sec)
mysql> SHOW VARIABLES like 'max_allowed_packet';
+--------------------+------------+
| Variable_name | Value |
+--------------------+------------+
| max_allowed_packet | 1073741824 |
+--------------------+------------+
1 row in set (0,00 sec)
但是当我尝试使用此命令时，php bin/console make:migration它仍然给了我这篇文章上面提到的相同错误，也尝试用wait_timeout相同的方法将变量更改为 300，它给了我相同的结果。:(
使用此命令sudo vim /var/log/mysql/error.log我得到这个：
2018-07-29T18:55:18.382164Z 0 [Warning] [MY-010909] [Server] /usr/sbin/mysqld: Forcing close of thread 8 user: 'alexandre'.
2018-07-29T18:55:20.288756Z 0 [System] [MY-010910] [Server] /usr/sbin/mysqld: Shutdown complete (mysqld 8.0.11) MySQL Community Server - GPL.
2018-07-29T18:55:20.642118Z 0 [System] [MY-010116] [Server] /usr/sbin/mysqld (mysqld 8.0.11) starting as process 31833
2018-07-29T18:55:21.704556Z 0 [Warning] [MY-010068] [Server] CA certificate ca.pem is self signed.
2018-07-29T18:55:21.720385Z 0 [System] [MY-010931] [Server] /usr/sbin/mysqld: ready for connections. Version: '8.0.11' socket: '/var/run/mysqld/mysqld.sock' port: 3306 MySQL Community Server - GPL.
更新： 我已经卸载了 mysql 和 php，并改为 mysql 5.7 和 php 7.2.7，php 的更改可能会解决这个问题关联 用户@jibe，如果有人仍然无法解决问题，我会让这两个其他链接 链接1 和链接2。