I am using the latest release of CentOS 7 on ovh.com VPS. I am going over Basic CentOS setup website, and it advises to change the SSH port (like many other websites that I've been reading now).

It looks like I am not able to do it thought, so I reversed everything to the original settings.

I was doing something like this:

After I did that I was getting something like this after running the journalctl -xn command

I've seen some posts about it on the Internet, but I was not able to find a precise answer, especially based on CentOS7, that I have.

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In general, I am at the default settings now, and what is advised in this article is good. When I do the changes sshd stops and it does not work, it is working currently, but it is root login at port 22.

How would I get this done?

What happens if you just uncomment the PermitRootLogin line and change it to no, eg:
etc, and then run "service sshd restart"?

Changing the ssh port should be very straight forward, I do it all the time, CentOS 7 included. You can have multiple ports as well, just add new lines, eg:
etc.

And this ...

I am logged in now. If I will disable the root login and then restart the sshd.service, will it not kick me out of the server, or something like this?

You could use reload instead of restart. However, if you are logged in as root it may kick you out after new setting takes effect.

No it won't, I do it all the time. Though as Emerson said, I'm not sure if the new setting would kick off an existing root ssh session since the new rule explicitly forbids it, though I doubt it. You do have another user, yes? I assume so since you already tried to shut off root SSH login earlier.

I will try this now. Thanks for your answers so far. If anybody needs info about xxx websites niche, I can let you know some things over email or Skype.

It is running, and it looks like everything is ok.

Simple question here - For key based authentication (something like an RSA key pair from puttygen) changing SSH port is 100% ok?

That's good, now how about adding a second listening port in addition to 22?
Just uncomment the "#Port 22" line, and add a second one below it with your desired port, then restarting sshd again?

When that's done you should be able to connect on either port, though you may need to play with firewall and SELinux rules. Once you verify the new port is working as expected, you can remove the "Port 22" line and restart again to limit your connections to just the new port, assuming you still want to after reading the article Emerson linked to.

Thanks for the info. I will leave it as is, and I will come back to it later on.

You probably need to tell selinux that it's ok for sshd to use an alternate port. The default centos7 has selinux enabled. You can allow an alternate port with this command.