Disclaimer: This article is a blogger original article, follow the CC 4.0 BY-SA copyright agreement, reproduced, please attach the original source link and this statement.
Firewall
1. Check the status of firewall ports
$ sudo ufw status
Status: active
To Action From
-- ------ ----
20,21,22,80,888,8888/tcp ALLOW Anywhere
39000:40000/tcp ALLOW Anywhere
888/tcp ALLOW Anywhere
2015 ALLOW Anywhere
443 ALLOW Anywhere
20,21,22,80,888,8888/tcp (v6) ALLOW Anywhere (v6)
39000:40000/tcp (v6) ALLOW Anywhere (v6)
888/tcp (v6) ALLOW Anywhere (v6)
2015 (v6) ALLOW Anywhere (v6)
443 (v6) ALLOW Anywhere (v6) 2. Turn off the firewall
$ sudo ufw disable3. Open the firewall
$ sudo ufw enableport
1. Open firewall port 2016
$ sudo ufw allow 2016
$ sudo ufw status
Status: active
To Action From
-- ------ ----
20,21,22,80,888,8888/tcp ALLOW Anywhere
39000:40000/tcp ALLOW Anywhere
888/tcp ALLOW Anywhere
2015 ALLOW Anywhere
2016 ALLOW Anywhere
443 ALLOW Anywhere
20,21,22,80,888,8888/tcp (v6) ALLOW Anywhere (v6)
39000:40000/tcp (v6) ALLOW Anywhere (v6)
888/tcp (v6) ALLOW Anywhere (v6)
2015 (v6) ALLOW Anywhere (v6)
2016 (v6) ALLOW Anywhere (v6)
443 (v6) ALLOW Anywhere (v6) 2. Firewall 2016 refused port access
$ sudo ufw deny 2016
Rule updated
Rule updated (v6)
$ sudo ufw status
Status: active
To Action From
-- ------ ----
20,21,22,80,888,8888/tcp ALLOW Anywhere
39000:40000/tcp ALLOW Anywhere
888/tcp ALLOW Anywhere
2015 ALLOW Anywhere
2016 DENY Anywhere
443 ALLOW Anywhere
20,21,22,80,888,8888/tcp (v6) ALLOW Anywhere (v6)
39000:40000/tcp (v6) ALLOW Anywhere (v6)
888/tcp (v6) ALLOW Anywhere (v6)
2015 (v6) ALLOW Anywhere (v6)
2016 (v6) DENY Anywhere (v6)
443 (v6) ALLOW Anywhere (v6) 3. Review the 2015 port occupancy process
$ lsof -i :2015
caddy 829 root 6u IPv6 14652 0t0 TCP *:2015 (LISTEN)