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MiracleLinux9.0 : SSH , Firewalld , NTP Server

1.Setting up SSH remote connection

SSH is a service to connect to a server remotely, and is basically running right after the OS installation, but the default settings are somewhat insecure.
In this section, we will configure the settings to change the default settings and increase the security of the ssh connection.

1.1 Change the configuration file of SSH service.

The configuration file for the SSH service is "/etc/ssh/sshd_config". Open the configuration file with vi editor

Line 21 "Port 22" This time change to "Port 2244" and proceed
Delete the "#" in line 24 "#ListenAddress 0.0.0.0
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.

Restart SSH

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

2.How to set up a firewall (firewalld)

In MiracleLinux, the firewall is set to firewalld by default, which is enabled when the OS is installed.

To briefly explain firewalld, when setting up a communication control policy, communication permission/blocking rules are applied to predefined zones, and the zones are 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

OR

※If the system is stopped
Active:The message "inactive (dead)" is displayed, indicating that firewalld is stopped

➁Show default zone settings

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

③About the "--permanent" option

In order to prevent the settings from being lost when the server is restarted or the "firewalld" service is restarted, use the "--permanent" option.
If the "--permanent" option is specified, the configuration will not be reflected in "firewalld" as it is, so it is necessary to reflect the configuration 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.Connect remotely from Windows

Setting up in Windows

Use "Tera Term" as a terminal emulator.
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" on the next screen.

If the information is correct, you should be able to log in normally as shown below.

4.NTP Server Settings

Build an NTP server to synchronize the server time with Japan Standard Time

①Chrony Installation and Configuration

②Restart chrony and enable chrony after restart

③NTP port allowed in firewall

④Check the status (operation) of chronyd.

If you can see the "*" mark, synchronization is complete.

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