Rocky Linux9.3 ; SSH、firewalld 、NTP Server

Contents

1.Remote connection via SSH
- 1.1 Edit SSH service configuration file
2.Firewall (firewalld) settings
- 2.1 How to use the "firewall-cmd" command to control "firewalld
- 2.2 Allow modified SSH port 2244
3.Remote connection from Windows
4.NTP Server

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".

# vi /etc/ssh/sshd_config

1	# 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 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

# $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

# systemctl restart sshd.service

1	# 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

# 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.

# 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.

# systemctl status firewalld
● firewalld.service - firewalld - dynamic firewall daemon
     Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; preset>
     Active: active (running) since Thu 2024-04-11 13:24:08 JST; 25min ago
       Docs: man:firewalld(1)
   Main PID: 72086 (firewalld)
      Tasks: 2 (limit: 10816)
     Memory: 27.1M
        CPU: 333ms
     CGroup: /system.slice/firewalld.service
             mq72086 /usr/bin/python3 -s /usr/sbin/firewalld --nofork --nopid

Apr 11 13:24:08 localhost.localdomain systemd[1]: Starting firewalld - dynamic >
Apr 11 13:24:08 localhost.localdomain systemd[1]: Started firewalld - dynamic f
※If stopped
Active: inactive (dead) is displayed, indicating that the firewall is stopped

# systemctl status firewalld

● firewalld.service - firewalld - dynamic firewall daemon

Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; preset>

Active: active (running) since Thu 2024-04-11 13:24:08 JST; 25min ago

Docs: man:firewalld(1)

Main PID: 72086 (firewalld)

Tasks: 2 (limit: 10816)

Memory: 27.1M

CPU: 333ms

CGroup: /system.slice/firewalld.service

mq72086 /usr/bin/python3 -s /usr/sbin/firewalld --nofork --nopid

Apr 11 13:24:08 localhost.localdomain systemd[1]: Starting firewalld - dynamic >

Apr 11 13:24:08 localhost.localdomain systemd[1]: Started firewalld - dynamic f

※If stopped

Active: inactive (dead) is displayed, indicating that the firewall is stopped

➁View 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:

# 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

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

1 2	# 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.

Start firewalld
# systemctl start firewalld

Stop firewalld
# systemctl stop firewalld

Start firewalld

# systemctl start firewalld

Stop firewalld

# systemctl stop firewalld

2.2 Allow modified SSH port 2244

# 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:

# 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

Setup in Windows
Start setting up a remote connection from Windows, using "Tera Term" as the 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.

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

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

①Chrony Installation and Configuration

# dnf -y install chrony

1	# dnf -y install chrony

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

# vi /etc/chrony.conf

Line 3　: Make it commented out and add under it

#pool 2.rocky.pool.ntp.org iburst

pool ntp.nict.jp iburst

②Restart chrony and enable chrony after system reboot

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

1 2	# systemctl enable chronyd.service # systemctl restart chronyd.service

③NTP port allowed in firewall

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

1 2	# firewall-cmd --add-service=ntp --permanent # firewall-cmd --reload

④Check chronyd status (behavior)

# 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

# chronyc sources

MS Name/IP address Stratum Poll Reach LastRx Last sample