If you happen to run into problems connecting to your server via SSH, or wish to test other things out by turning firewalld on or off in CentOS, follow the instructions below.
To turn off firewalld, enter this command: systemctl stop firewalld
To turn on firewalld, enter this command: systemctl start firewalld
For checking the status of firewalld after you have enter either commands above, use this command: systemctl firewalld