1.Setting up remote connection by 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 SSH service configuration file changes
Modify the configuration file to change the SSH service settings.
The SSH service configuration file is "/usr/etc/ssh/sshd_config". Open the configuration file with a vi editor
# vi /usr/etc/ssh/sshd_config
Line 20 : Uncomment and change to any port number other than the Wernon port.
Port 2244
Line 22 : Uncomment
ListenAddress 0.0.0.0
Line 39 : Uncomment and change(Disable root logins)
PermitRootLogin prohibit-password
Restart SSH
# 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 allow SSH port 2244 in the following firewall settings.
2.How to set up a firewall (firewalld)
In openSUSE, the firewall is set to firewalld by default and is enabled during OS installation.
①Check firewalld operation status
# firewall-cmd --state
If "firewalld" is running, "running" will be displayed; if it is not running, "not running" will be displayed.
➁Show default zone settings
# firewall-cmd --list-all
public (default, active)
target: default
ingress-priority: 0
egress-priority: 0
icmp-block-inversion: no
interfaces: ens33
sources:
services: dhcpv6-client ssh
ports:
protocols:
forward: yes
masquerade: no
forward-ports:
source-ports:
icmp-blocks:
rich rules:
In the above example, the "public" zone is the "default" setting and is assigned to the "eth0" NIC, and the services "dhcpv6-client" and "ssh" are allowed, etc.
➂About the "--permanent" option
In order to prevent the settings from being lost when the server is restarted or the "firewalld" service is restarted, the "--permanent" option must be used.
To prevent the settings from being lost when the server is restarted or the "firewalld" service is restarted, the "--permanent" option must be used to configure the settings. In this case, if the "--permanent" option is specified, the settings will not be reflected in "firewalld" as they are, so it is necessary to reflect the settings 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
3.Remote connection from Windows
Configuration 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 the following information on the next screen.
Host : Server IP Address
TCP port : SSH port number changed above
After clicking "OK," click "Continue" on the security confirmation screen.
Enter the following information on the next screen.
User name : General Login Username
Passphrase : Password for the above user
If the information is correct, you should be able to log in successfully.
4. NTP Server Settings
Install Chrony and build an NTP server for time synchronization. Note that NTP uses 123/UDP.
4.1 Chrony Install
# zypper -n install chrony
4.2 Chrony Settings
# vi /etc/chrony.conf
# Line 8 : Comment
#! pool pool.ntp.org iburst
pool ntp.nict.jp iburst
# Around line 30: Add the range where time synchronization is permitted.
allow 192.168.11.0/24
Enable Chrony and start the program
# systemctl start chronyd
# systemctl enable chronyd
4.3 Open NTP port
If Firewalld is enabled, permission for NTP service is required. Note that NTP uses 123/UDP.
# firewall-cmd --add-service=ntp --permanent
success
# firewall-cmd --reload
success
4.4 operation check
# chronyc sources
MS Name/IP address Stratum Poll Reach LastRx Last sample
===============================================================================
^- ntp-b2.nict.go.jp 1 6 17 45 -982us[ -982us] +/- 6579us
^* ntp-b3.nict.go.jp 1 6 17 45 -63us[ +672us] +/- 5651us
^- ntp-a3.nict.go.jp 1 6 17 45 -866us[ -866us] +/- 6513us
^- ntp-k1.nict.jp 1 6 17 45 -913us[ -913us] +/- 3812us
^+ 172-105-192-74.ip.linode> 2 6 17 46 +426us[+1161us] +/- 5830us