How do I open a port number in CentOS7

There are two things that could be at play here:

1. Ensure the firewall rules are in place

For Firewalld, the way to check would be the following:

First get the active zones. It will most likely be public, but there may be others.

$ firewall-cmd --get-active-zones

Then, once you have the active zones you can check to make sure the firewall is opened where you expect it to be. I'll use public in the example, but as mentioned, use whatever the active zones are from above.

$ sudo firewall-cmd --zone=public --list-all

You're hoping to see something like the following, with 2223/tcp listed in the ports: section.

$ sudo firewall-cmd --zone=public --list-all
public (active)
  target: default
  icmp-block-inversion: no
  interfaces: eth0
  sources:
  services: ssh dhcpv6-client
  ports: 2223/tcp
  protocols:
  masquerade: no
  forward-ports:
  source-ports:
  icmp-blocks:
  rich rules:

If it is not there, but you are sure that you added the rule, you may need to reload your firewall rules.

$ sudo firewall-cmd --reload

For more details, there are a few common scenarios in Linode's FirewallD doc.

2. Ensure the service is listening

If all the results from above show the port being open, it's possible that it is, but there is nothing listening. The output of the following will show what could be listening on that port.

$ sudo ss -tulpn

Or look for only services that include 2223 in the output.

$ sudo ss -tulpn | grep 2223

Today I can access this port, but i do not do anything on this linode .

i am confused now…

Thank you for replay.

firewall-cmd --get-active-zones

public interfaces: eth0

sudo firewall-cmd --zone=public --list-all

public (active) target: default ports: 2223/tcp

sudo ss -tulpn

Netid State Recv-Q Send-Q Local Address:Port Peer Address:P tcp LISTEN 0 128 *:2223 *:* ) tcp LISTEN 0 128 :::2223 :::* )