ubuntu firewall ?

[ubroot]

sudo ufw default deny


The ubuntu firewall only uses the above sentence.
Is it safe?

[CharlesA]

Here's what the man page shows about that command:

default allow|deny|reject DIRECTION
change the default policy for traffic going DIRECTION, where DIRECTION is one of
incoming, outgoing or routed. Note that existing rules will have to be migrated
manually when changing the default policy. See RULE SYNTAX for more on deny and
reject.

Verify you have the correct rules in place by running the following:

sudo ufw status

[TheFu]

For typical home users, it is sufficient.
There are exceptions for systems running network services. If you didn't specifically setup up a service, don't worry.

[ipv2]

there is always the gui app if you wish to tweak the ufw :

sudo apt install gufw