Contents
1.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.
1.1 Edit SSH service configuration file
Modify the configuration file to change the SSH service settings.
The SSH service configuration file is "/etc/ssh/sshd_config".
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# vi /etc/ssh/sshd_config |
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# $OpenBSD: sshd_config,v 1.104 2021/07/02 05:11:21 dtucker Exp $ # This is the sshd server system-wide configuration file. See # sshd_config(5) for more information. # This sshd was compiled with PATH=/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin # The strategy used for options in the default sshd_config shipped with # OpenSSH is to specify options with their default value where # possible, but leave them commented. Uncommented options override the # default value. # To modify the system-wide sshd configuration, create a *.conf file under # /etc/ssh/sshd_config.d/ which will be automatically included below Include /etc/ssh/sshd_config.d/*.conf # If you want to change the port on a SELinux system, you have to tell # SELinux about this change. # semanage port -a -t ssh_port_t -p tcp #PORTNUMBER # Port 2244 #AddressFamily any ListenAddress 0.0.0.0 #ListenAddress :: #HostKey /etc/ssh/ssh_host_rsa_key #HostKey /etc/ssh/ssh_host_ecdsa_key #HostKey /etc/ssh/ssh_host_ed25519_key # Ciphers and keying #RekeyLimit default none # Logging #SyslogFacility AUTH #LogLevel INFO # Authentication: #LoginGraceTime 2m PermitRootLogin prohibit-password #StrictModes yes #MaxAuthTries 6 #MaxSessions 10 |
Line 21 "Port 22" This time change to "Port 2244" and proceed
Delete the "#" in line 23 "#ListenAddress 0.0.0.0"
Line 40, "#PermitRootLogin prohibit-password", delete "#".
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
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# systemctl restart sshd.service |
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
The firewall is set to firewalld as default and is enabled during OS installation.
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
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# firewall-cmd --state running If "firewalld" is running, the message "running" will be displayed; if it is not running, the message "not running" will be displayed. |
OR
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# systemctl status firewalld ● firewalld.service - firewalld - dynamic firewall daemon Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; preset: enabled) Active: active (running) since Fri 2025-12-26 12:07:32 JST; 55min ago Docs: man:firewalld(1) Main PID: 871 (firewalld) Tasks: 2 (limit: 16855) Memory: 38.4M (peak: 61.2M) CPU: 740ms CGroup: /system.slice/firewalld.service └─871 /usr/bin/python3 -s /usr/sbin/firewalld --nofork --nopid Dec 26 12:07:31 localhost systemd[1]: Starting firewalld - dynamic firewall daemon... Dec 26 12:07:32 localhost systemd[1]: Started firewalld - dynamic firewall daemon. |
※When stopped
Active: inactive (dead) is displayed.
➁View default zone settings
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# firewall-cmd --list-all public (active) target: default icmp-block-inversion: no interfaces: ens160 sources: services: cockpit dhcpv6-client ssh ports: protocols: forward: no masquerade: no forward-ports: source-ports: icmp-blocks: rich rules: |
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, the setting is not reflected in "firewalld" as it is, so it is necessary to use "fiewall-cmd --reload" to reflect the setting.
As an example, to use the HTTP service permanently without initialization even if the system is rebooted
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# firewall-cmd --add-service=http --permanent # firewall-cmd --reload |
④How to start/stop
Since "firewalld" is controlled by "systemd", use the "systemctl" command to start and stop it.
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Start firewalld # systemctl start firewalld Stop firewalld # systemctl stop firewalld |
2.2 Allow modified SSH port 2244
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# firewall-cmd --add-port=2244/tcp --permanent success # firewall-cmd --reload success # firewall-cmd --list-all public (active) target: default icmp-block-inversion: no interfaces: ens160 sources: services: cockpit dhcpv6-client ssh ports: 2244/tcp protocols: forward: no masquerade: no forward-ports: source-ports: icmp-blocks: rich rules: |
2244 ports have been added
3.Remote connection from Windows
How to connect using Tabby Terminal
Specify the SSH port number changed with the" -p 2244" option.
C:\Users\xxxxx>ssh huong@192.168.11.83 -p 2244
huong@192.168.11.83's password:
Activate the web console with: systemctl enable --now cockpit.socket
Last login: Fri Dec 26 12:41:49 2025 from 192.168.11.6
huong@Lepard:~$
4.NTP Server
Build an NTP server to synchronize the server time with Japan Standard Time
①Chrony Installation and Configuration
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# dnf -y install chrony |
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# vi /etc/chrony.conf Line 3 : Comment it out and add it below. #pool 2.rocky.pool.ntp.org iburst pool ntp.nict.jp iburst |
②Enable chrony and restart.
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# systemctl enable chronyd.service # systemctl restart chronyd.service |
③NTP port allowed in firewall
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# firewall-cmd --add-service=ntp --permanent # firewall-cmd --reload |
④Check chronyd status (behavior)
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# chronyc sources MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== ^+ ntp-a2.nict.go.jp 1 6 17 26 -509us[ +463us] +/- 5991us ^* ntp-a3.nict.go.jp 1 6 17 25 +455us[+1427us] +/- 5404us ^+ ntp-k1.nict.jp 1 6 17 26 -246us[ +726us] +/- 3729us ^+ ntp-b3.nict.go.jp 1 6 17 26 -94us[ +877us] +/- 5726us |
If it is marked with *, it has been synchronized.
