Overview here
To initialize a database after it has been installed natively on a host, it needs to be initialized first. Part of this is to use the initdb command. It can be invoked using the pg_ctl initdb command/subcommand.
It must be run as the user that will own the database server process for security reasons. This can be overriden by for example allowing group control, however this is inadvisable. NOTE because initdb will create data directories it might not have permissions to create those, so they should be created by root or a sudo user first then use the chown command to give the postgres user ownership of those directories.
Sometimes it's necessary to remove all trace of a database, particularly for testing and redeployment situations. Here we'll see how to completely get rid of all traces of it.
First, get rid of the OS package, in this case using apt on Debian-based systems.
sudo apt --purge remove postgresql
sudo apt purge postgresql*
sudo apt --purge remove postgresql postgresql-doc postgresql-common
Perhaps there's optional packages that were installed, let's grep for any package names using dpkg to see if there's any others.
dpkg -l | grep postgres
Then remove (purge) the rest and pretend all the packages are included in the variable $PGSQL_PKGS_FOR_PURGE.
sudo apt --purge remove $PGSQL_PKGS_FOR_PURGE
Use the coreutil command, rm to remove the directories and files used by PostgreSQL. Using the -rf arguments to remove all directories recursively & forcefully to override any warnings about deletion.
sudo rm -rf /var/lib/postgresql/
sudo rm -rf /var/log/postgresql/
sudo rm -rf /etc/postgresql/