MySQL 连接数设置操作（Too many connections）及设置md5值的加密密码

mysql在使用过程中，发现连接数超了~~~~

[root@linux-node1 ~]# mysql -u glance -h 192.168.1.17 -p
Enter password:
ERROR 1040 (08004): Too many connections

解决办法，这也是centos7下修改mysql连接数的做法：
1）临时修改
MariaDB [(none)]> show variables like "max_connections";
+-----------------+-------+
| Variable_name | Value |
+-----------------+-------+
| max_connections | 214 |
+-----------------+-------+
1 row in set (0.00 sec)
MariaDB [(none)]> set GLOBAL max_connections=1000;
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> show variables like "max_connections";
+-----------------+-------+
| Variable_name | Value |
+-----------------+-------+
| max_connections | 1000 |
+-----------------+-------+
1 row in set (0.00 sec)

2）永久修改：
配置/etc/my.cnf
[mysqld]新添加一行如下参数：
max_connections=1000
重启mariadb服务，再次查看mariadb数据库最大连接数，可以看到最大连接数是214，并非我们设置的1000。
MariaDB [(none)]> show variables like 'max_connections';
+-----------------+-------+
| Variable_name | Value |
+-----------------+-------+
| max_connections | 214 |
+-----------------+-------+
这是由于mariadb有默认打开文件数限制。可以通过配置/usr/lib/systemd/system/mariadb.service来调大打开文件数目。

配置/usr/lib/systemd/system/mariadb.service
[Service]新添加两行如下参数：
LimitNOFILE=10000
LimitNPROC=10000

重新加载系统服务，并重启mariadb服务
systemctl --system daemon-reload
systemctl restart mariadb.service

再次查看mariadb数据库最大连接数，可以看到最大连接数已经是1000
MariaDB [(none)]> show variables like 'max_connections';
+-----------------+-------+
| Variable_name | Value |
+-----------------+-------+
| max_connections | 1000 |
+-----------------+-------+

=============================================================================
mysql设置32位md5值的密文密码

如下，设置admin用户的密码为"123!@#ad"
mysql> select * from admin_user;
+----+----------+--------------------------------------------------------------------+----------------------+---------------------+
| id | username | password                                                 | create_time    | update_time  |
+----+---------------+---------------------------------------------------------------+----------------------+---------------------+
|  1 | admin       | 4ad597c11755c50d00457f4420365763 |  1538979880 |  1538979880 |
+----+---------------+---------------------------------------------------------------+----------------------+---------------------+
1 row in set (0.00 sec)

mysql> update admin_user set username = 'admin',password = md5('123!@#ad') where id = 1

mysql> select * from admin_user;
+----+----------+--------------------------------------------------------------------+----------------------+---------------------+
| id | username | password                                                 | create_time    | update_time  |
+----+---------------+---------------------------------------------------------------+----------------------+---------------------+
|  1 | admin       | 0fy866r8662a70d85632u90563212687 |  1541676212  |  1541676212 |
+----+---------------+---------------------------------------------------------------+----------------------+---------------------+
1 row in set (0.00 sec)