Check Status of SSH Service
Verify current status of SSH service by using systemctl command.
# systemctl status sshd.service â sshd.service - OpenSSH server daemon Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled) Active: active (running) since Sat 2020-08-08 17:59:18 PKT; 2s ago Docs: man:sshd(8) man:sshd_config(5) Main PID: 1564 (sshd) Tasks: 1 (limit: 5916) Memory: 1.2M CGroup: /system.slice/sshd.service ââ1564 /usr/sbin/sshd -D -oCiphers=aes256-gcm@openssh.com,chacha20-poly1305@openssh.com,aes256-ctr,aes256-cbc,> Aug 08 17:59:18 centos-8.centlinux.com systemd[1]: Starting OpenSSH server daemon... Aug 08 17:59:18 centos-8.centlinux.com sshd[1564]: Server listening on 0.0.0.0 port 22. Aug 08 17:59:18 centos-8.centlinux.com sshd[1564]: Server listening on :: port 22. Aug 08 17:59:18 centos-8.centlinux.com systemd[1]: Started OpenSSH server daemon.
You can see that the service is running on default SSH port number 22.
Change SSH Default Port in CentOS 8
SSH daemon/service configurations are located in /etc/ssh/sshd_config file. We can tweak them to customize SSH service according to our requirements.
Initially there is no Port directive in this file, instead, the SSH service is using the default ssh port number 22.
Let’s add a Port directive in sshd_config file by using echo command.
# echo "Port 2222" >> /etc/ssh/sshd_config
This one shot setting is quiet enough to change ssh default port number.
Configure SELinux to Allow SSH custom Port
Default SELinux configuration does not allow any service to run on a non-default port. Therefore, we have to configure SElinux to allow SSH to use port 2222/tcp.
We need semanage command to configure SELinux settings. If you are using a minimal installed CentOS 8 system then it is not available on your system. Install policycoreutils-python-utils package to get semanage command.
Then use semanage command to add port 2222/tcp to type ssh_port_t.
# semanage port -a -t ssh_port_t -p tcp 2222
Configure Firewall to Allow SSH custom Port
List down allowed ports or services in Linux firewall.
# firewall-cmd --list-all public (active) target: default icmp-block-inversion: no interfaces: ens33 sources: services: cockpit dhcpv6-client ssh ports: protocols: masquerade: no forward-ports: source-ports: icmp-blocks: rich rules:
SSH service is by default allowed in most distributions of Linux including CentOS / RHEL 8.
Now, we need to block this ssh service and allow our new ssh port in Linux firewall.
# firewall-cmd --permanent --remove-service=ssh success # firewall-cmd --permanent --add-port=2222/tcp success # firewall-cmd --reload success
Restart SSH Service
Restart SSH Service to apply changes that we have made in sshd_config file.
# systemctl restart sshd.service
Verify status of SSH Service.
# systemctl status sshd.service â sshd.service - OpenSSH server daemon Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled) Active: active (running) since Sat 2020-08-08 18:13:37 PKT; 14s ago Docs: man:sshd(8) man:sshd_config(5) Main PID: 10376 (sshd) Tasks: 1 (limit: 5916) Memory: 1.2M CGroup: /system.slice/sshd.service ââ10376 /usr/sbin/sshd -D -oCiphers=aes256-gcm@openssh.com,chacha20-poly1305@openssh.com,aes256-ctr,aes256-cbc> Aug 08 18:13:37 centos-8.centlinux.com systemd[1]: Stopped OpenSSH server daemon. Aug 08 18:13:37 centos-8.centlinux.com systemd[1]: Starting OpenSSH server daemon... Aug 08 18:13:37 centos-8.centlinux.com sshd[10376]: Server listening on 0.0.0.0 port 2222. Aug 08 18:13:37 centos-8.centlinux.com sshd[10376]: Server listening on :: port 2222. Aug 08 18:13:37 centos-8.centlinux.com systemd[1]: Started OpenSSH server daemon.
You can see that the service is now running on non-default port 2222 instead of default ssh port number 22.
Access SSH Service using custom Port
Try to access SSH service using ssh and sftp commands from the default ssh port.
# ssh root@centos-8.centlinux.com ssh: connect to host centos-8.centlinux.com port 22: Connection refused # sftp root@centos-8.centlinux.com ssh: connect to host centos-8.centlinux.com port 22: Connection refused Connection closed. Connection closed
It confirms that Linux Firewall is not allowing the traffic through port 22.
Now, access the SSH service by using ssh command from the non-default ssh port.
# ssh root@centos-8.centlinux.com -p 2222 The authenticity of host '[centos-8.centlinux.com]:2222 ([192.168.116.206]:2222)' can't be established. ECDSA key fingerprint is SHA256:skGj4xg0w+jIQtrfF8AOdfItgcXUQQu+bWUFfvws1Hk. Are you sure you want to continue connecting (yes/no/[fingerprint])? yes Warning: Permanently added '[centos-8.centlinux.com]:2222,[192.168.116.206]:2222' (ECDSA) to the list of known hosts. root@centos-8.centlinux.com's password: Last login: Sat Aug 8 17:59:01 2020 #
Similarly, for sftp.
# sftp -P 2222 root@centos-8.centlinux.com root@centos-8.centlinux.com's password: Connected to root@centos-8.centlinux.com. sftp>