Asterisk -- install on Ubuntu 18.04 + 20.04
Follow the instructions on this site: https://linuxize.com/post/how-to-install-asterisk-on-ubuntu-20-04/
However, I skipped two parts, "Installing DAHDI and LibPRI" and I also skipped to Configure Firewall at the bottom.

This text is part of a users guide and there is an index page to look at.


Skip DAHDI

• sudo apt update
• sudo apt install wget build-essential git autoconf subversion pkg-config libtool

Move on to Installing Asterisk:

$ sudo make menuselect

Opus! Important!
If your window is too wide, not all options will show! :-) Exit, correct window size and sudo make menuselect one more time! This may occur if you connect with SSH to your Asterisk-PBX server.

Warning!
Applications >> [X] macro

Scroll the page and press [Enter] to select "macro" for the build.

jakob@pangolin:/usr/src/asterisk-18$ sudo make basic-pbx
Installing basic-pbx config files...
Installing file configs/basic-pbx/README
Installing file configs/basic-pbx/asterisk.conf
Installing file configs/basic-pbx/cdr.conf
Installing file configs/basic-pbx/cdr_custom.conf
Installing file configs/basic-pbx/confbridge.conf
Installing file configs/basic-pbx/extensions.conf
Installing file configs/basic-pbx/indications.conf
Installing file configs/basic-pbx/logger.conf
Installing file configs/basic-pbx/modules.conf
Installing file configs/basic-pbx/musiconhold.conf
Installing file configs/basic-pbx/pjsip.conf
Installing file configs/basic-pbx/pjsip_notify.conf
Installing file configs/basic-pbx/queues.conf
Installing file configs/basic-pbx/voicemail.conf
Updating asterisk.conf
jakob@pangolin:/usr/src/asterisk-18$


Configuring Firewall
I stopped here.
I continued with FreeePBX

$ sudo -s ... continue as root.