Symptoms

• An attempt to login into Plesk panel fails with the error:

  DB query failed: SQLSTATE[08004] [1040] Too many connections

• The MySQL service status shows this to be active but a code exited and a failure status:

  # service mysql status
  ● mysql.service - LSB: Start and stop the mysql database server daemon 
  Loaded: loaded (/etc/init.d/mysql) 
  Active: active (running) since Tue 2020-06-30 16:16:24 CEST; 15min ago 
  Process: 29285 ExecStop=/etc/init.d/mysql stop (code=exited, status=1/FAILURE) 
  Process: 31746 ExecStart=/etc/init.d/mysql start (code=exited, status=0/SUCCESS) 
  CGroup: /system.slice/mysql.service 
  ├─2077 /bin/bash /usr/bin/mysqld_safe 
  ├─3150 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib/mysql/plugin --user=mysql --skip-log-error --pid-file... 
  └─3151 logger -t mysqld -p daemon.error

• The service does not stop if this operation is attempted but changes to a failed status:

  # systemctl stop mysql.service 
  
  ● mysql.service - LSB: Start and stop the mysql database server daemon 
  Loaded: loaded (/etc/init.d/mysql) 
  Active: *failed (Result: exit-code) since Tue 2020-06-30 16:34:51 CEST; 12s ago 
  Process: 7254 ExecStop=/etc/init.d/mysql stop (code=exited, status=1/FAILURE) 
  Process: 31746 ExecStart=/etc/init.d/mysql start (code=exited, status=0/SUCCESS) 

Cause

MySQL or its subprocesses are stuck and unresponsive.

Resolution

1. Connect to the server via SSH

2. Retry to stop MySQL service manually:

   # systemctl stop mysql.service

3. Check if any mysql process still is running with:

   # pidof -c /usr/sbin/mysqld

   And:

   # ps awufx | grep mysql | grep -v grep

4. If any output was obtained on the previous step then Kill all these mysql processes manually by taking its IDs for example:

   * From:

   # pidof -c /usr/sbin/mysqld
   7327

   # ps awufx | grep mysql | grep -v grep
   root 7187 0.0 0.0 21820 3504 ? S 21:32 0:00 /bin/bash /usr/bin/mysqld_safe 
   mysql 7327 0.1 2.0 624472 81944 ? Sl 21:32 0:00 \_ /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib/mysql/plugin --user=mysql --skip-log-error --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/run/mysqld/mysqld.sock --port=3306 
   root 7328 0.0 0.0 23684 2476 ? S 21:32 0:00 \_ logger -t mysqld -p daemon.error

    

   * Run the kill command with all the above processes IDs as follows:

   # kill -9 7187 7327 7328

5. Be sure that there the mysql process is no longer running, an empty output is expected, otherwise repeat step 4:

   # pidof -c /usr/sbin/mysqld

6. Restart the MySQL service:

   # systemctl start mysql.service