When you first create a new CentOS server, there are a few configuration steps that you should take early on as part of the basic setup. This will increase the security and usability of your server and will give you a solid foundation for subsequent actions.
To log into your server, you will need to know your server’s public IP address. You will also need the password or, if you installed an SSH key for authentication, the private key for the root user’s account. If you have not already logged into your server, you may want to follow our documentation on how to connect to your Droplet with SSH, which covers this process in detail.
If you are not already connected to your server, log in as the root user now using the following command (substitute the highlighted portion of the command with your server’s public IP address):
- ssh root@your_server_ip
Accept the warning about host authenticity if it appears. If you are using password authentication, provide your root password to log in. If you are using an SSH key that is passphrase protected, you may be prompted to enter the passphrase the first time you use the key each session. If this is your first time logging into the server with a password, you may also be prompted to change the root password.
The root user is the administrative user in a Linux environment, and it has very broad privileges. Because of the heightened privileges of the root account, you are discouraged from using it on a regular basis. This is because part of the power inherent with the root account is the ability to make very destructive changes, even by accident.
As such, the next step is to set up an alternative user account with a reduced scope of influence for day-to-day work. This account will still be able to gain increased privileges when necessary.
Once you are logged in as root, you can create the new user account that we will use to log in from now on.
This example creates a new user called sammy, but you should replace it with any username that you prefer:
- adduser sammy
Next, set a strong password for the sammy
user:
- passwd sammy
You will be prompted to enter the password twice. After doing so, your user will be ready to use, but first we’ll give this user additional privileges to use the sudo
command. This will allow us to run commands as root when necessary.
Now, we have a new user account with regular account privileges. However, we may sometimes need to do administrative tasks.
To avoid having to log out of our normal user and log back in as the root account, we can set up what is known as “superuser” or root privileges for our normal account. This will allow our normal user to run commands with administrative privileges by putting the word sudo
before each command.
To add these privileges to our new user, we need to add the new user to the wheel group. By default, on CentOS, users who belong to the wheel group are allowed to use the sudo
command.
As root, run this command to add your new user to the wheel group (substitute the highlighted word with your new username):
- usermod -aG wheel sammy
Now, when logged in as your regular user, you can type sudo
before commands to perform actions with superuser privileges.
Firewalls provide a basic level of security for your server. These applications are responsible for denying traffic to every port on your server, except for those ports/services you have explicitly approved. CentOS has a service called firewalld
to perform this function. A tool called firewall-cmd
is used to configure firewalld
firewall policies.
Note: If your servers are running on DigitalOcean, you can optionally use DigitalOcean Cloud Firewalls instead of firewalld
. We recommend using only one firewall at a time to avoid conflicting rules that may be difficult to debug.
First install firewalld
:
- dnf install firewalld -y
The default firewalld
configuration allows ssh
connections, so we can turn the firewall on immediately:
- systemctl start firewalld
Check the status of the service to make sure it started:
- systemctl status firewalld
Output● firewalld.service - firewalld - dynamic firewall daemon
Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled)
Active: active (running) since Thu 2020-02-06 16:39:40 UTC; 3s ago
Docs: man:firewalld(1)
Main PID: 13180 (firewalld)
Tasks: 2 (limit: 5059)
Memory: 22.4M
CGroup: /system.slice/firewalld.service
└─13180 /usr/libexec/platform-python -s /usr/sbin/firewalld --nofork --nopid
Note that it is both active
and enabled
, meaning it will start by default if the server is rebooted.
Now that the service is up and running, we can use the firewall-cmd
utility to get and set policy information for the firewall.
First let’s list which services are already allowed:
- firewall-cmd --permanent --list-all
Outputpublic (active)
target: default
icmp-block-inversion: no
interfaces: eth0 eth1
sources:
services: cockpit dhcpv6-client ssh
ports:
protocols:
masquerade: no
forward-ports:
source-ports:
icmp-blocks:
rich rules:
To see the additional services that you can enable by name, type:
- firewall-cmd --get-services
To add a service that should be allowed, use the --add-service
flag:
- firewall-cmd --permanent --add-service=http
This would add the http
service and allow incoming TCP traffic to port 80
. The configuration will update after you reload the firewall:
- firewall-cmd --reload
Remember that you will have to explicitly open the firewall (with services or ports) for any additional services that you may configure later.
Now that we have a regular non-root user for daily use, we need to make sure we can use it to SSH into our server.
Note: Until verifying that you can log in and use sudo
with your new user, we recommend staying logged in as root. This way, if you have problems, you can troubleshoot and make any necessary changes as root. If you are using a DigitalOcean Droplet and experience problems with your root SSH connection, you can log into the Droplet using the DigitalOcean Console.
The process for configuring SSH access for your new user depends on whether your server’s root account uses a password or SSH keys for authentication.
If you logged in to your root account using a password, then password authentication is enabled for SSH. You can SSH to your new user account by opening up a new terminal session and using SSH with your new username:
- ssh sammy@your_server_ip
After entering your regular user’s password, you will be logged in. Remember, if you need to run a command with administrative privileges, type sudo
before it like this:
- sudo command_to_run
You will be prompted for your regular user password when using sudo
for the first time each session (and periodically afterwards).
To enhance your server’s security, we strongly recommend setting up SSH keys instead of using password authentication. Follow our guide on setting up SSH keys on CentOS to learn how to configure key-based authentication.
If you logged in to your root account using SSH keys, then password authentication is disabled for SSH. You will need to add a copy of your public key to the new user’s ~/.ssh/authorized_keys
file to log in successfully.
Since your public key is already in the root account’s ~/.ssh/authorized_keys
file on the server, we can copy that file and directory structure to our new user account.
The simplest way to copy the files with the correct ownership and permissions is with the rsync
command. This will copy the root user’s .ssh
directory, preserve the permissions, and modify the file owners, all in a single command. Make sure to change the highlighted portions of the command below to match your regular user’s name:
Note: The rsync
command treats sources and destinations that end with a trailing slash differently than those without a trailing slash. When using rsync
below, be sure that the source directory (~/.ssh
) does not include a trailing slash (check to make sure you are not using ~/.ssh/
).
If you accidentally add a trailing slash to the command, rsync
will copy the contents of the root account’s ~/.ssh
directory to the sudo
user’s home directory instead of copying the entire ~/.ssh
directory structure. The files will be in the wrong location and SSH will not be able to find and use them.
- rsync --archive --chown=sammy:sammy ~/.ssh /home/sammy
Now, back in a new terminal on your local machine, open up a new SSH session with your non-root user:
- ssh sammy@your_server_ip
You should be logged in to the new user account without using a password. Remember, if you need to run a command with administrative privileges, type sudo
before it like this:
- sudo command_to_run
You will be prompted for your regular user password when using sudo
for the first time each session (and periodically afterwards).
At this point, you have a solid foundation for your server. You can install any software you need on it now.
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I just wanted to note that you can actually skip steps 2 and 3, because there’s a user called “centos” that’s already created. If you used an SSH key to secure root access to your droplet, that key was also associated with the “centos” user automatically. So the only thing remaining is to prevent root logins through SSH - see step 5 of “Initial Server Setup with CentOS 7”.
Thanks for the tutorials, they help me with my higher studies.