Is it possible to have two versions of PostgreSQL Server on same Fedora 37 Server?

Thanks to several answers and comments to my question and also some further investigation, the setup finally works as desired.

Before taking any action, the situation was as following:

• Operating System: Fedora 37 Server (command line only)
• PostgreSQL Server 14 installed as "available version" out of Fedora 37 Repos

This is the procedure applied to get desired setup:

1. Remove PostgreSQL Server 14

(as root): dnf remove postgres*

2. Add latest PG repository for Fedora 37

(as root): dnf install -y https://download.postgresql.org/pub/repos/yum/reporpms/F-37-x86_64/pgdg-fedora-repo-latest.noarch.rpm

3. Install PostgreSQL 11 and 15

(as root): dnf install postgresql11-server

And here, it came with error message: "...matches were filtered out by modular filtering for argument...". I'll cut it short, it got solved by following command (I don't know why exactly, but it worked):

(as root): dnf module reset postgresql*

This time, this worked:

(as root): dnf install postgresql11-server postgresql15-server 

4. Initialize the Databases In this step, I tried recommended option with initdb -D <folder> but I ended up in a trouble in one of following steps. This is the way it worked on my server:

(as root): /usr/bin/postgresql-11-setup initdb
(as root): /usr/bin/postgresql-15-setup initdb

5. Amend configuration in your postgresql.conf files, example with vim editor.

(as root): vim /var/lib/pgsql/11/data/postgresql.conf
(as root): vim /var/lib/pgsql/15/data/postgresql.conf

If you're not sure where the files are, you can find them like this: find / -iname 'postgresql.conf'. I added "listen to all" and changed port. The port is mandatory to be changed, otherwise, second instance trying to address same port will fail to start.

listen_addresses = '*'
port = 54311

Make sure to remove comment prefix "#". For PG11, I used 54311 as shown, for PG15 I used 54315. Just make sure these are different and don't collide with other standard ports.

6. Enable and start the servers

(as root): systemctl enable postgresql-11
(as root): systemctl start postgresql-11
(as root): systemctl status postgresql-11

(as root): systemctl enable postgresql-15
(as root): systemctl start postgresql-15
(as root): systemctl status postgresql-15

7. Let's not forget the firewall

(as root): firewall-cmd --permanent --add-port=54311/tcp
(as root): firewall-cmd --permanent --add-port=54315/tcp
(as root): systemctl restart firewalld.service

8. Setup user(s) and database(s)... The servers should be up-and-running now. But you have no users and created database. This is not really the part of setting up the server, but I'll give examples for newbies.

(as root): su postgres
(as postgres): psql -p 54311
(psql): 
(psql): alter user postgres with password '<pwd_for_postgresql>';
(psql): create user myusername with password '<pwd>';
(psql): create database educ_db owner=myusername;

You need to repeat this, but connect to the other port -p 54315. Don't forget to allow acces in the pg_hba.conf file. Here is an example for version 11:

(as root): vim /var/lib/pgsql/11/data/pg_hba.conf
# My Use-Case Setup -------------------------------------------------
host    educ_db         myusername      all                     md5
# -------------------------------------------------------------------

Don't forget to restart the PG server(s) or just reboot at all. Have fun!