OpenSUSE : change ssh port / use a cutom ssh port

For this exemple, our custom ssh port will be 52222.

Edit /etc/ssh/sshd_config:

# vim /etc/ssh/sshd_config

Uncomment Port 22 and change it to Port 52222.

Note: You can add several times the Port directive to allow several ports. This can be usefull first to not be locked out of the server. For example:

Port 22
Port 52222

Restart the ssh deamon:

# systemctl restart sshd.service

Do not close your current ssh session and test if you can localy connect via ssh with the new port:

$ ssh user@localhost -p 52222

If it works you can exit the test ssh connection.

Now we will need to allow this new port in the firewall.

To do so, edit /etc/sysconfig/SuSEfirewall2.d/services/sshd:

# vim /etc/sysconfig/SuSEfirewall2.d/services/sshd

Change TCP="ssh" to TCP="52222" (this will only allow port 52222 for ssh) or to TCP="ssh 52222" if you want both ports.

Note: this is possible because there is FW_CONFIGURATIONS_EXT="sshd" in your /etc/sysconfig/SuSEfirewall2 config file. Known terms (mapping between well known ports and services, ex: ssh=22) are in /etc/services, it's not advised to modify this file.

Now restart the firewall:

# systemctl restart SuSEfirewall2.service
or
# rcSuSEfirewall2 restart

Question: Why did we tested local ssh connection before modifying the firewall rules? Because the change we made only affects external connections (i.e. from the internet) so local connection are not restricted by firewall port filtering.

Now we can safely exit the remote ssh connection.

Now to connect to the server we have to specify the ssh port:

$ ssh user@example.org -p 52222

or add a custom entry in .ssh/config (single user) or /etc/ssh_config (all users):

Host host_alias
    Hostname example.org
    Port 52222
    User user

and simply connect with:

$ ssh host_alias