Warning: mysqli_real_connect(): (HY000/2002): Connection refused in /var/www/html/wordpress/wp-includes/wp-db.php on line 1626 I'm just starting to code and I try to host a Wordpress website on a server of my school.
However, as soon as I upload the website on the Wordpress interface with the plugin "all-in-one migration", the database crashed. Wordpress gives me the error :

Warning: mysqli_real_connect(): (HY000/2002): Connection refused in /var/www/html/wordpress/wp-includes/wp-db.php on line 1626


When I check my database, I find it :

● mariadb.service - MariaDB 10.3.22 database server
   Loaded: loaded (/lib/systemd/system/mariadb.service; enabled; vendor preset: enabled)
   Active: deactivating (final-sigterm) (Result: timeout) since Thu 2020-06-18 21:23:34 UTC; 28min ago
     Docs: man:mysqld(8)
           https://mariadb.com/kb/en/library/systemd/
  Process: 10644 ExecStartPre=/usr/bin/install -m 755 -o mysql -g root -d /var/run/mysqld (code=exited, status=0/SUCCESS)
  Process: 10645 ExecStartPre=/bin/sh -c systemctl unset-environment _WSREP_START_POSITION (code=exited, status=0/SUCCESS)
  Process: 10647 ExecStartPre=/bin/sh -c [ ! -e /usr/bin/galera_recovery ] &amp;&amp; VAR= ||   VAR=`/usr/bin/galera_recovery`; [ $? -eq 0 ]   &amp;&amp; systemctl set-environment _WSREP_START_POSITION=$VAR || exit 1
 Main PID: 10695 (mysqld)
   Status: "Waiting for page cleaner"
    Tasks: 3 (limit: 563)
   Memory: 65.1M
   CGroup: /system.slice/mariadb.service
           └─10695 /usr/sbin/mysqld

Jun 18 21:23:40 genius systemd[1]: Starting MariaDB 10.3.22 database server...
Jun 18 21:23:41 genius mysqld[10695]: 2020-06-18 21:23:41 0 [Note] /usr/sbin/mysqld (mysqld 10.3.22-MariaDB-0+deb10u1) starting as process 10695 ...
Jun 18 21:39:50 genius systemd[1]: mariadb.service: State 'stop-sigterm' timed out. Skipping SIGKILL.


And, of course, when I try to enter my database, I get the code :

ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (111)


I tried to restart the database, but it doesn't return any response.

By searching on StackOverflow, a few answers suggest changing localhost  to a local IP like 127.0.0.1 in the file "wp-config.php", but it didn't change anything.

Can you help me please ?
first check wp-config.php for this 4 lines

// ** MySQL settings - You can get this info from your web host ** //
/** The name of the database for WordPress */
define( 'DB_NAME', 'database_name_here' );
/** MySQL database username */
define( 'DB_USER', 'username_here' );
/** MySQL database password */
define( 'DB_PASSWORD', 'password_here' );
/** MySQL hostname */
define( 'DB_HOST', 'localhost' );


then Check Your Database Host Information
and if you failed do this action
add define('WP_ALLOW_REPAIR', true); in your wp-config.php
and after you have done ,navigate with http://yourwebsite.com/wp-admin/maint/repair.php.
and better before doing disactivate all pluging via ftp
rename plugins to plugins.deactivate.
repair wordpress
and finnaly Update WordPress Site URL in wp_options tables
Update WordPress Site URL