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

# vi /etc/ssh/sshd_config

#       $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 22
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

Restart SSH

# systemctl restart sshd.service

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

# firewall-cmd --state
running
If "firewalld" is running, "running" will be displayed; if it is not running, "not running" will be displayed.

OR

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

➁Show default zone settings

# 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

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

# firewall-cmd --add-service=http --permanent
# firewall-cmd --reload

④How to start and stop

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

Start firewalld
# systemctl start firewalld
Stop firewalld
# systemctl stop firewalld

2.2 Allow modified SSH port 2244

# firewall-cmd --add-port=2244/tcp --permanent
# firewall-cmd --reload
# 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:

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

4.NTP Server Settings

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

①Chrony Installation and Configuration

# dnf -y install chrony

# vi /etc/chrony.conf
Line 3 : comment out and add under it
#pool 2.cloudlinux.pool.ntp.org iburst
pool ntp.nict.jp iburst

# systemctl enable chronyd.service
# systemctl restart chronyd.service

# firewall-cmd --add-service=ntp --permanent
# firewall-cmd --reload

# chronyc sources
MS Name/IP address Stratum Poll Reach LastRx Last sample
==============================================================
^+ ntp-b2.nict.go.jp 1 6 77 27 -50us[ -342us] +/- 5432us
^+ ntp-b3.nict.go.jp 1 6 77 26 +103us[ +103us] +/- 5681us
^* ntp-k1.nict.jp 1 6 77 26 -250us[ -544us] +/- 3445us
^+ ntp-a2.nict.go.jp 1 6 77 27 -211us[ -503us] +/- 5513us

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