OpenSUSE Tumbleweed : Firewall , SSH、NTP Server

1.Setting up remote connection by SSH

SSH is a service for connecting remotely to a server and is basically running immediately after the OS is installed, but the default settings are somewhat insecure.
Here we will configure the default settings to increase the security of ssh connections.

1.1 SSH service configuration file changes

Modify the configuration file to change the SSH service settings.
The SSH service configuration file is "/usr/etc/ssh/sshd_config". Open the configuration file with a vi editor

Restart SSH

If this is not done, the next time you reboot, you will not be able to connect remotely via SSH. Please allow SSH port 2244 in the following firewall settings.

2.How to set up a firewall (firewalld)

In openSUSE, the firewall is set to firewalld by default and is enabled during OS installation.

①Check firewalld operation status

If "firewalld" is running, "running" will be displayed; if it is not running, "not running" will be displayed.

OR

※If stopped
Active: inactive (dead) is displayed, indicating that firewalld is stopped

➁Show default zone settings

In the above example, the "public" zone is the "default" setting and is assigned to the "eth0" NIC, and the services "dhcpv6-client" and "ssh" are allowed, etc.

➂About the "--permanent" option
In order to prevent the settings from being lost when the server is restarted or the "firewalld" service is restarted, the "--permanent" option must be used.
To prevent the settings from being lost when the server is restarted or the "firewalld" service is restarted, the "--permanent" option must be used to configure the settings. In this case, if the "--permanent" option is specified, the settings will not be reflected in "firewalld" as they are, so it is necessary to reflect the settings using "fiewall-cmd --reload".
As an example, to use the HTTP service permanently without being initialized even if the system is rebooted

④How to start and stop

Since "firewalld" is controlled by "systemd", use the "systemctl" command to start and stop it.

2.2  Allow modified SSH port 2244

3.Remote connection from Windows

Configuration in Windows

Start setting up a remote connection from Windows, using "Tera Term" as the terminal emulator.
Start Tera Term, cancel the startup screen, and then select "New Connection" from "File" in the Tera Term menu.

Enter the following information on the next screen.
Host : Server IP Address
TCP port : SSH port number changed above

After clicking "OK," click "Continue" on the security confirmation screen.

Enter the following information on the next screen.
User name : General Login Username
Passphrase : Password for the above user

If the information is correct, you should be able to log in successfully.

4. NTP Server Settings

Install Chrony and build an NTP server for time synchronization. Note that NTP uses 123/UDP.

4.1 Chrony Install

4.2 Chrony Settings

4.3 Open NTP port

If Firewalld is enabled, permission for NTP service is required. Note that NTP uses 123/UDP.

4.4 operation check