Listening to services running that use port 80

Listen in on the ports being used on your server.  To do so, run the command

netstat -a | grep tcp

If netstat is not install, then you'll be prompted to run the install script

sudo apt install net-tools

Response

Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
  net-tools
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 196 kB of archives.
After this operation, 864 kB of additional disk space will be used.
Get:1 http://azure.archive.ubuntu.com/ubuntu focal/main amd64 net-tools amd64 1.60+git20180626.aebd88e-1ubuntu1 [196 kB]
Fetched 196 kB in 1s (332 kB/s)
Selecting previously unselected package net-tools.
(Reading database ... 96037 files and directories currently installed.)
Preparing to unpack .../net-tools_1.60+git20180626.aebd88e-1ubuntu1_amd64.deb ...
Unpacking net-tools (1.60+git20180626.aebd88e-1ubuntu1) ...
Setting up net-tools (1.60+git20180626.aebd88e-1ubuntu1) ...
Processing triggers for man-db (2.9.1-1) ...

Run netstat again

This time the response is

tcp        0      0 localhost:postgresql    0.0.0.0:*               LISTEN
tcp        0      0 localhost:domain        0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:9001            0.0.0.0:*               LISTEN
tcp        0      0 localhost:37609         0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:ssh             0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:http            0.0.0.0:*               LISTEN
tcp        0      0 localhost:http-alt      0.0.0.0:*               LISTEN
tcp        0      0 localhost:6379          0.0.0.0:*               LISTEN
tcp6       0      0 [::]:8983               [::]:*                  LISTEN
tcp6       0      0 [::]:ssh                [::]:*                  LISTEN
tcp6       0      0 [::]:http               [::]:*                  LISTEN
tcp6       0      0 ip6-localhost:6379      [::]:*                  LISTEN

Or using

sudo netstat -ltnp

Generates the response

Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 127.0.0.1:5432          0.0.0.0:*               LISTEN      1006/postgres
tcp        0      0 127.0.0.53:53           0.0.0.0:*               LISTEN      681/systemd-resolve
tcp        0      0 0.0.0.0:9001            0.0.0.0:*               LISTEN      769/python3
tcp        0      0 127.0.0.1:37609         0.0.0.0:*               LISTEN      1235/uwsgi
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      830/sshd: /usr/sbin
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      17560/nginx: master
tcp        0      0 127.0.0.1:8080          0.0.0.0:*               LISTEN      1235/uwsgi
tcp        0      0 127.0.0.1:6379          0.0.0.0:*               LISTEN      919/redis-server 12
tcp6       0      0 :::8983                 :::*                    LISTEN      740/java
tcp6       0      0 :::22                   :::*                    LISTEN      830/sshd: /usr/sbin
tcp6       0      0 :::80                   :::*                    LISTEN      17560/nginx: master
tcp6       0      0 ::1:6379                :::*                    LISTEN      919/redis-server 12