How to change mysql parameter without restart mysql?

Try these single and simple command from your mysql cli, to change mysql global parameter on the fly (it’s means no need to restart the service)

mysql> set global max_connections=400;

you can check the results using this command

mysql> show global variables;

always be reminded that parameter has been setup using above command will be not persist across restart, you need to put the parameter in /etc/my.cnf so the changes will persist across reboot.