I followed the steps on slack build and installed Postgresql using the user and group Postgres with no password and now struggling to login to database.

Database is running but can't connect.

Do I need to give the user Postgres a password first? Actually tried changing it and it can't be changed apparently.

Thanks inn advance

What does "can't connect" mean? Please detail.
Have you got your database storage(cluster) initialized with initdb?
I'd suggest to always switch to user postgres for maintenance (even connecting) on console - use: su - postgres
If you want to connect to the db as a different user, use: psql -U postgres postgres
(given the default db is called postgres)

Here's a short version of the "RTFM":
https://www.postgresql.org/docs/11/install-short.html

The latest version of Postgresql is 12.0
https://www.postgresql.org/download/

@abga the short version of RTFM is OK just instead of "make" I use "gmake -j2"

If look at https://www.postgresql.org/developer/roadmap/ today is must out PostgreSQL 12.1

plisken, if need you can read my howto (in Russian)

* Go to your cluster dir (``/var/lib/pgsql/10.2/data`` for postgres installed from slackbuilds)
* Open ``pg_hda.conf``
* add the following line ``local postgres postgres trust``
* restart posgres ``/etc/rc.d/rc.postgresql restart``
* connect ``$ sudo -u postgres psql``
* set password: ``# \password``
* remove line you added to ``pg_hda.conf``
* restart posgres ``/etc/rc.d/rc.postgresql restart``
* connect using password

PostgreSQL 12.1 · 2019-11-14
https://www.postgresql.org/docs/12/release-12-1.html

What is the reason to use 12 if slackbuilds contain 10?

IlyaK, it's your choice what is use.
I prefer a new opportunities and stability.
The databases should be updated, and not stand still.

My bad, apologies...

Seems like I was in such a rush to test one thing that I forgot that I had actually set a password during compile or install.

Anyway, all fine, achieved what I set out to, database imported with;

psql dbname < backup.sql

It was the password being requested by the above command that had me stumped, but as I say, I forgot I had actually set it.

Thanks for all replies and interest...

As a point of clarification - what is listed in SBo isn't to be taken as somehow an endorsed version per say. While the maintainer of that SBo may in fact endorse a specific version of a software package, that doesn't necessarily mean it's the most preferred option out there. The only thing that can be reliably ascertained is "this is a specific combination that is known to work."

In the case of Postgresql, I would say that 10 is a bit old at this point, and I made a trivial change (I think it was just the version number) to build the 11 series. I generally follow a project's most recent stable release, so I'll jump to Postgresql 12 soon as well. You can offer changes back to the SBo project if you think that the scripts for building that software are outdated. (Recommended that you first contact the script maintainer directly, however.)