uname -or
2.6.32-754.6.3.el6.x86_64 GNU/Linux

uname -a
Linux vps-xxx-xxx.example.com 2.6.32-754.6.3.el6.x86_64 #1 SMP Tue Oct 9 17:27:49 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

cat /etc/*elease`
CentOS release 6.10 (Final)
CentOS release 6.10 (Final)
CentOS release 6.10 (Final)

SELECT VERSION();
5.5.61

select User,Host from mysql.user;

+----------------+-----------+
| User           | Host      |
+----------------+-----------+
| admin_test     | %         |
| admin_test     | localhost |
| root           | localhost |
| roundcube      | localhost |
+----------------+-----------+

1. service mysqld stop
Stopping mysqld:                                           [OK]

2. mysqld_safe --skip-grant-tables &
[1] 713
[root@vps-xxx-xxx ~]# 190113 14:44:01 mysqld_safe Logging to '/var/log/mysqld.lo                                                                g'.
190113 14:44:01 mysqld_safe Starting mysqld daemon with databases from /var/lib/                                                                mysql

3. mysql
Welcome to the MySQL monitor.  Commands end with ; or g.
Your MySQL connection id is 1
Server version: 5.5.61 MySQL Community Server (GPL) by Remi

Copyright (c) 2000, 2018, 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.

4. UPDATE mysql.user SET Password=PASSWORD('123456qwerty7890') WHERE User='admin_test';

Query OK, 0 rows affected (0.01 sec)
Rows matched: 2  Changed: 0  Warnings: 0

5. FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)

6. exit;
Bye

7. mysqladmin -u root -p shutdown
Enter password:

190113 14:48:21 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ende                                                         d
[1]+  Done                    mysqld_safe --skip-grant-tables

8. service mysqld start
Starting mysqld:                                           [  OK  ]

xx.xxx.xxx.xxx/phpmyadmin