How to change SSH Default Port in CentOS 8

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>