环境

Ubuntu 版本信息：

$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 22.04 LTS
Release:	22.04
Codename:	jammy

开放端口，删除已经开放的端口

ufw - program for managing a netfilter firewall

查看帮助信息：

$ ufw --help

Usage: ufw COMMAND

Commands:
 enable                          enables the firewall
 disable                         disables the firewall
 default ARG                     set default policy
 logging LEVEL                   set logging to LEVEL
 allow ARGS                      add allow rule
 deny ARGS                       add deny rule
 reject ARGS                     add reject rule
 limit ARGS                      add limit rule
 delete RULE|NUM                 delete RULE
 insert NUM RULE                 insert RULE at NUM
 prepend RULE                    prepend RULE
 route RULE                      add route RULE
 route delete RULE|NUM           delete route RULE
 route insert NUM RULE           insert route RULE at NUM
 reload                          reload firewall
 reset                           reset firewall
 status                          show firewall status
 status numbered                 show firewall status as numbered list of RULES
 status verbose                  show verbose firewall status
 show ARG                        show firewall report
 version                         display version information

Application profile commands:
 app list                        list application profiles
 app info PROFILE                show information on PROFILE
 app update PROFILE              update PROFILE
 app default ARG                 set default application policy

查看防火墙状态：

$ sudo ufw status
Status: active

开放 22 端口：

$ sudo ufw allow 22
Rule added
Rule added (v6)

添加完成，查看防火墙状态：

$ sudo ufw status
Status: active

To                         Action      From
--                         ------      ----
22                         ALLOW       Anywhere                  
22 (v6)                    ALLOW       Anywhere (v6)

添加 8888 端口，并且只接受 TCP 协议：

$ sudo ufw allow 8888/tcp
Rule added
Rule added (v6)

添加完成，查看防火墙状态：

$ sudo ufw status
Status: active

To                         Action      From
--                         ------      ----
22                         ALLOW       Anywhere                  
8888/tcp                   ALLOW       Anywhere                  
22 (v6)                    ALLOW       Anywhere (v6)             
8888/tcp (v6)              ALLOW       Anywhere (v6)

查看防火墙状态编号列表的规则：

$ sudo ufw status numbered
Status: active

     To                         Action      From
     --                         ------      ----
[ 1] 22                         ALLOW IN    Anywhere                  
[ 2] 8888/tcp                   ALLOW IN    Anywhere                  
[ 3] 22 (v6)                    ALLOW IN    Anywhere (v6)             
[ 4] 8888/tcp (v6)              ALLOW IN    Anywhere (v6)

删除编号 3 的规则：

$ sudo ufw delete 3
Deleting:
 allow 22
Proceed with operation (y|n)? y
Rule deleted (v6)

删除完成，重新查看防火墙状态编号列表的规则：

$ sudo ufw status numbered
Status: active

     To                         Action      From
     --                         ------      ----
[ 1] 22                         ALLOW IN    Anywhere                  
[ 2] 8888/tcp                   ALLOW IN    Anywhere                  
[ 3] 8888/tcp (v6)              ALLOW IN    Anywhere (v6)

继续删除编号 3 的规则：

$ sudo ufw delete 3
Deleting:
 allow 8888/tcp
Proceed with operation (y|n)? y
Rule deleted (v6)

删除完成，重新查看防火墙状态编号列表的规则：

$ sudo ufw status numbered
Status: active

     To                         Action      From
     --                         ------      ----
[ 1] 22                         ALLOW IN    Anywhere                  
[ 2] 8888/tcp                   ALLOW IN    Anywhere