Disable SSH Password Authentication For Specific User Or Group

We can allow or deny SSH access for users and/or a whole group using “/etc/ssh/sshd_config” file in Linux. The sshd_config file has a parameter named “Match” which will help you to disable SSH password authentication for users or groups.

Let us first see how to disable password authentication for a specific user.

Edit “/etc/ssh/sshd_config” file using your favorite editor as root or sudo user:

$ sudo nano /etc/ssh/sshd_config

First, remove the default authentication method by comment out the following line:

#PasswordAuthentication yes

Next, add the following lines at the end:

[...]
Match User senthil
    PasswordAuthentication no

Please note that Match is effective “until either another Match line or the end of the file.” If a keyword appears in multiple Match blocks that are satisfied, only the first instance of the keyword is applied.

As per the above example, we have disabled the SSH password authentication for the user called “senthil”. Replace “senthil” with your own username. Save and close the file. Restart ssh service to take effect the changes:

$ sudo systemctl restart ssh

Now try to login as user “senthil” via SSH:

$ ssh senthil@192.168.225.53

You will see the following error message:

senthil@192.168.225.53: Permission denied (publickey).

Disable SSH password authentication for a group

To disable SSH password authentication for a specific Group, just replace the user name with the group name in the sshd_config file.

Match Group mygroup
    PasswordAuthentication no

Replace “mygroup” in the above configuration with your own group name.

Don’t forget to restart the ssh service to apply the changes.

Disable SSH password authentication for multiple users

You can deny SSH password authentication for multiple users by mentioning the user names with comma-separated like below:

Match User senthil,kumar
    PasswordAuthentication no

The above example configuration will prevent SSH password authentication for users “senthil” and “kumar”.

Disable SSH password authentication for all users except root user

In some Linux systems, you might want to allow SSH password authentication for “root” user only and disable it for all other users. If so, add the following line in sshd_config file at the end:

Match User !root
    PasswordAuthentication no

Restrict SSH password authentication by host or IP address

Not just user or group, we can deny SSH password authentication by host or IP address as well.

For example, the following example will prevent SSH access from a host that contains the IP address:

Match Address 192.168.225.37
       PasswordAuthentication no

To limit SSH password authentication for a specific range of IP addresses, add this:

Match Address 192.168.225.*
      PasswordAuthentication no

And this example will deny SSH access using password from a host that contains the hostname:

Match Address hostname
       PasswordAuthentication no

For more details, refer man pages.

$ man sshd_config