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Rocky Linux8.6 : SSH、firewall、NTP

1. Setting up SSH remote connection

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

The SSH service configuration file is "/etc/ssh/sshd_config".

Line 17 "Port 22" This time change to "Port 2244" and proceed.

Delete the "#" in line 20 "#ListenAddress"
Change "PermitRootLogin yes" to "PermitRootLogin no" on line 44.
Since the root user already knows the user name and can log in to the server with administrator privileges once the password is known, the setting is set to deny this.

Restart SSH

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. How to set up a firewall (firewalld)

In Rocky, 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"

① Check firewalld operation status


➁ View 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
The "--permanent" option must be used to configure the settings.
If the "--permanent" option is specified, it is necessary to use "fiewall-cmd --reload" to reflect the settings, as they are not reflected in "firewalld" as they are.

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" Passphrasee and click "OK".

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

① Chrony Installation and Configuration

②Restart chrony and enable chrony after system reboot

③NTP port release in firewall

④Checking chronyd status

If it is marked with *, it has been synchronized. (It takes about 10 minutes to synchronize after startup.)

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