Ubuntu firewall usage example

$ sudo ufw status
Status: active

$ sudo ufw disable

Firewall stopped and disabled on system startup

$ sudo ufw enable

Command may disrupt existing ssh connections. Proceed with operation (y|n)? y

Firewall is active and enabled on system startup

$ sudo ufw app list

Available applications:

  OpenSSH

$ sudo ufw  allow 4848

Rule added

Rule added (v6)

$ sudo ufw status

Status: active

To                         Action      From

--                         ------      ----

4848                       ALLOW       Anywhere

4848 (v6)                  ALLOW       Anywhere (v6)

$ sudo ufw delete allow 4848

Rule deleted

Rule deleted (v6)

$ sudo ufw allow from 192.168.0.0/23 proto tcp to any port 4848

WARN: Rule changed after normalization

Rule added

$ sudo ufw status

Status: active

To                         Action      From

--                         ------      ----

4848/tcp                   ALLOW       192.168.0.0/23

$ sudo ufw status verbose

Status: active

Logging: on (low)

Default: deny (incoming), allow (outgoing), disabled (routed)

New profiles: skip

To                         Action      From

--                         ------      ----

4848/tcp                   ALLOW IN    192.168.0.0/23

Adding the --dry-run option to a ufw command will output the resulting rules, but not apply them. For example, the following is what would be applied if opening the HTTP port:

$ sudo ufw --dry-run allow http

$ sudo ufw  allow https

Rule added

Rule added (v6)

$ sudo ufw  allow http

Rule added

Rule added (v6)

$ sudo ufw status verbose

Status: active

Logging: on (low)

Default: deny (incoming), allow (outgoing), disabled (routed)

New profiles: skip

To                         Action      From

--                         ------      ----

4848/tcp                   ALLOW IN    192.168.0.0/23

443                        ALLOW IN    Anywhere

80                         ALLOW IN    Anywhere

443 (v6)                   ALLOW IN    Anywhere (v6)

80 (v6)                    ALLOW IN    Anywhere (v6)

$ sudo ufw reload

Firewall reloaded

$ sudo 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
 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

You can also use gufw for a graphical interface to manage your firewall:

$ sudo apt install gufw