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CentOS Stream9 ; SSH , Firewalld , NTP

1.Setting up remote connection via 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.

Line 21 "Port 22" changed to "Port 2244" this time
Delete the "#" in line 24 "#ListenAddress
Line 41, "#PermitRootLogin prohibit-password", delete "#".
The root user can log in to the server with administrator privileges if the user name is already known and the password is known, so the settings are set to deny this.

SSH restart

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

2.Firewall (firewalld) settings

On CentOS9 ST, the firewall is set to firewalld by default and is enabled during OS installation.

To briefly explain "firewalld," when setting communication control policies, communication permission/blocking rules are applied to predefined zones, and these zones are then assigned to each NIC (network adapter).

2.1 How to use the "firewall-cmd" command to control "firewalld"

1)Command to check the status and settings of "firewalld

①Check firewalld operation status


Active: active (running)と表示されています

➁View default zone settings

In the above example, we can see that the services "cockpit", "dhcpv6-client", "ssh" are allowed, etc.

③About the "--permanent" option
To prevent the settings from disappearing when the server is restarted or the "firewalld" service is restarted, the "--permanent" option must be used to configure the settings. If the "--permanent" option is specified, the settings will not be reflected in "firewalld" as is, so it is necessary to reflect the settings using "fiewall-cmd --reload".
As an example, to use the HTTP service permanently without initialization even if the system is rebooted

④How to start/stop
Since "firewalld" is controlled by "systemd", use the "systemctl" command to start and stop it.

2.2  Release modified SSH port 2244

2244 ports have been added

3.Remote connection from Windows

Configuration in Windows
The terminal emulator is "Tera Term".
Start Tera Term, cancel the startup screen, and then select "New Connection" from "File" in the Tera Term menu.

Enter your own settings in the "Server IP Address" and "TCP Port Number" fields. Finally, click "OK.

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

Enter "User name" and "Passphrase" and click "OK

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

4.NTP Server Settings

Build an NTP server to synchronize the server time with Japan Standard Time
①Chrony Installation and Configuration

Change time synchronization server

②Restart chrony and enable chrony after system reboot

③NTP port release in firewall

④Check chronyd status (behavior)

If it is marked with *, it has been synchronized.

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