Ahmed Rabea Smaha's questions

1 - Create the file /etc/apt/sources.list.d/pgdg.list and add a line for the repository

deb [arch=amd64] http://apt.postgresql.org/pub/repos/apt/ focal-pgdg main

2 - Import the repository signing key, and update the package lists

wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -

sudo apt-get update

3 - install posgtresql

sudo apt-get install postgresql-12 postgresql-client-12 postgresql-12 postgresql-contrib libpq-dev postgresql-server-dev-12

4 - install pgadmin 4

sudo apt-get install pgadmin4

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package pgadmin4 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'pgadmin4' has no installation candidate

hope I'm in the right place.

I'm following this instruction : https://tecadmin.net/install-zabbix-on-ubuntu/

Instead of installing the zabbix-release_4.2-1+bionic_all.deb, I downloaded the zabbix-release_4.4-1+bionic_all.deb file.

By the installation of the zabbix-server-mysql and zabbix-frontend-php and zabbix-agent, the following error-output shows up:

ahmedsmaha@DarkStar:~$ sudo apt install zabbix-server-mysql zabbix-frontend-php zabbix-agent
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 zabbix-server-mysql : Depends: libmysqlclient20 (>= 5.7.11) but it is not installable
                       Recommends: snmpd but it is not going to be installed
E: Unable to correct problems, you have held broken packages.