Force change ssh port on CentOS / RHEL 7/8 and Fedora 31/30/29 with SELinux

In this guide, we will see how to change the SSH service port on CentOS 7/8, RHEL 7/8, and Fedora 31/30/29 using SELinux running in Enforcing mode. When SELinux running Enforce Mode it Enforce of SELinux Policy and deny access based on SELinux Policy rules. The standard SSH port on most Linux / Unix systems is TCP port 22. It can be easily changed to a custom port that is not used by other applications in the system.

When SELinux is running in Enforcing mode, you need to reset the port to be set so that the policy rules that control access can accept ssh services for binding. Follow the steps discussed below to change the SSH port of SELinux running Enforcing mode on a CentOS / RHEL / Fedora server or desktop.

Step 1: Back up your current SSH configuration

Log in to your CentOS / RHEL / Fedora system and back up your current ssh daemon configuration file.

date_format=`date +%Y_%m_%d:%H:%M:%S`
sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config_$date_format

confirm:

$ ls /etc/ssh/sshd_config*
/etc/ssh/sshd_config  /etc/ssh/sshd_config_2019_09_05:21:40:10

Step 2: Change the SSH service port

Use your favorite text editor-vi, vim, nano e.t.c to open the SSH service configuration file.

sudo vi /etc/ssh/sshd_config

Find the line with:

#Port 22

Uncomment the port line and set a new service port to use. I will use port 33000.

Port 33000

Save your changes and close the file.

Step 3: Allow new SSH ports on SELinux

The default port marked as SSH is 22.

$ semanage port -l | grep ssh
ssh_port_t                     tcp      22

If you want to allow sshd Bind to the configured network port, you need to change the port type to ssh_port_t.

sudo semanage port -a -t ssh_port_t -p tcp 33000

Confirm that the new port has been added to the list of ports allowed by ssh.

$ semanage port -l | grep ssh
ssh_port_t                     tcp      33000, 22

Step 4: Open the SSH port on Firewalld

It is always recommended to keep the firewall service running and allow only trusted services.

sudo firewall-cmd --add-port=33000/tcp --permananet
sudo firewall-cmd --reload

If Firewalld is not installed, use yum to install and start the service.

sudo yum -y install firewalld
sudo systemctl enable --now firewalld
sudo firewall-cmd --add-port=33000/tcp --permanent
sudo firewall-cmd --reload

You can now delete the ssh service.

sudo firewall-cmd --remove-service=ssh --permanent
sudo firewall-cmd --reload

Step 5: Restart the sshd service

Restart the ssh service for the changes to take effect.

sudo systemctl restart sshd

Verify the ssh listening address.

$ netstat -tunl | grep 33000
tcp        0      0 0.0.0.0:33000           0.0.0.0:*               LISTEN     
tcp6       0      0 :::33000                :::*                    LISTEN    

Other articles:

How to disable SSH reverse DNS lookup in Linux / Unix systems

How to set up two factor (2FA) authentication for SSH on CentOS / RHEL

Easy way to create SSH tunnel on Linux CLI

How to change or update SSH key password on Linux / Unix

Ssh cheat sheet for Linux SysAdmins

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