Verified and Tested 05/9/15
This how-to will help you with your initial setup on CentOS 7 so that you can successfully secure your server while giving you the peace of mind knowing your server is protected. With the addition of systemd CentOS 7 is very different than its older predecessors. With any server, the primary goal should always be security. Many users are victims of malicious infiltrations on their servers due to the lack of security boundaries established from the beginning. Let us begin on the right path by laying our foundation with security.
What Do You Need?
You need a CentOS 7 server that is configured with a static IP address. If you do not have a server already, consider a top-quality server from Atlantic.net and be up in under 30 seconds.
To get started, log in to your CentOS 7 server via SSH or the VNC Console located here. Atlantic.Net Cloud servers are setup as minimal installations in order to avoid having unnecessary packages from being installed and never used. If some software packages that you’re used to using aren’t installed by default, feel free to install them as needed.
Let’s make sure that your server is fully up-to-date.
With the server up-to-date, we can continue the process and secure your server.
Update the CentOS 7 Root Password
By default, your Atlantic.Net servers are automatically set with secure passwords. However, we still recommend updating your password after creating your server and every 60-90 days thereafter in order to ensure it remains secure. A minimum of 8 characters, including lowercase, uppercase and numbers are recommended to increase the level of security.
Type the following command to activate your request and follow the on screen instructions to update/confirm your root password:
Create a new user with sudo privileges
After successfully updating your password, it’s recommended that you create a new user with sudo/root permissions. Since the common admin user for many Linux Operating Systems like CentOS 7 is “root”, we’re going to make a new admin user that will be used for day-to-day administration tasks. Creating a new user with root permissions will increase the security in the way your server is accessed. Unwanted users target the root user because they know its the default admin user but when you create a new user with sudo/root permissions and then disable the default root user, they will never know what user to login with.
Type the following command to create your new user replacing “user1” with your own username and confirm.
Create a password for that user by typing the following command to activate your request and following the on screen instructions to update/confirm your “user1” password:
Once you have created a new user and created the password for that user, it is time to add the user to the sudo wheel group. In CentOS 7 once you add them to the sudo wheel group they are automatically assigned sudo/root permissions. Run the following command to add the user to the sudo wheel group.
gpasswd -a user1 wheel
Finally when you have created the user with sudo/root permissions, you can exit your session and log back in with your “user1” to verify the changes that were made. Alternatively, you can run the following command and switch users from root to “user1” which will then ask you for that users password.
su - user1
Configure SSH Access
In Linux systems, port 22 is the default port for remote connections via SSH. By changing the ssh port, you will increase the security of your server in preventing brute force attacks and unwanted users from reaching your server using the default port. For this tutorial I will use Port 5022 as an example.
Open your SSH Configuration file, find the Port line, remove the # and change 22 number to your Custom port Save and exit.
sudo vi /etc/ssh/sshd_config
In order for your system to update the settings from the SSH Configuration file, we must restart sshd.
sudo systemctl restart sshd.service
SSH has now been configured to use Port 5022 and if you attempt to login using Port 22, your login will fail. However, do not exit your session as we need to configure the custom port on the firewalls configuration part first, which we will configure in the upcoming steps.
Limit Root Access
Since we’ve created a new user with root permissions and created a custom ssh port, there’s no need keep the actual root user available and vulnerable over SSH on your server. Let us restrict the root users access to be available on the local server and granting permission to the new user over SSH only.
Open the SSH Configuration file, find the PermitRootLogin line, remove the # and change it from yes to no.
sudo vi /etc/ssh/sshd_config
In order for your system to update the new settings in the SSH Configuration file, we must restart the sshd service.
sudo systemctl restart sshd.service
Note: In making those changes you will now have the root user disabled so you must log into your server with the “user1” that you created. However, do not exit your session, we must configure the custom port on the firewall in the upcoming steps.
Create a Private SSH Key
Private/Public SSH Keys are great additional features that increases security in the method a server is accessed. However, it takes a bit more effort to setup. The question is, Is your server worth the extra security? If you would like to implement the following security features you can continue with the following steps. Let us proceed and generate the SSH Key.
If you want to change the location where the SSH Key will be saved, you can specify it here. However, the default location where its stored should be OK. Press enter when you are prompted with the following question then enter a pass phrase, unless you don’t want one.
Enter file in which to save the key (/home/user1/.ssh/id_rsa):
This is the default page when installing SSH Keys on a CentOS 7 server
Configuring the SSH Key is crucial, we must copy the full key string to a Word/ Notepad Document. The Key can be viewed in the following location with the cat command.
Copy the SSH key beginning with ssh-rsa and ending with [email protected] into a Word/ Notepad document so we can add it to the config file later on.
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDNcnc3pMOytM7xgwZHUX0Wi/O78hDvLUmQVtKn8Qk1ijBY82jVftKXKRhf8toNkgm9jaZmfapLa7ynzUG4jbFjyy8H+iEs1R8P7eu+e8/fmGwjorbMFuWdoi7h2CldoqKTdMEb/dMNxjNMzBbovl3XtZviQGm4/TMVO1hHxy85JR8zAtNFu7liaP7IonexNrOGhY8CjqRcBsceQLkl1MlX7cWaWAMqd6jQnAvggTLerI9P286AP8Sk4uColj7GKOljj8X6J/2pcjp9v2IvJOqwC/zLwUKZ6qTEV6SrfdbjopoCVvpXkVhmcbHX5Xv1gwynO+vTkpPFwVTjSnAai71L [email protected]
Once the SSH Key is stored safely the directory for the SSH Keys needs limited permissions which only the owner can read, write and execute the file.
chmod 700 .ssh
Within the SSH directory, a file containing the SSH Key must to be added, simply using your editor (in this case VI) the following location:
Paste the SSH Key then save and exit using the VI format.
Finally, we have to limit the permissions of the authorized_keys file that we just created so only owner can read and write.
chmod 600 .ssh/authorized_keys
We could now verify that the key is working by closing the session and typing [email protected] or your servers hostname in your SSH Console . Furthermore, for more information you can click “here” to see our How To Generate and Use SSH Keys article.
Basic Firewall Rules
By default your Atlantic.Net’s CentOS 7 Server is loaded with a default firewall named firewalld
which uses the firewall
-cmd in order to configure its rules. We must first start the Firewall service with the following:
sudo systemctl start firewalld
Next, we’re going to add a rule to allow the custom SSH Port 5022 that was created earlier so it can access the server publicly. At the same time, we’re going to remove the previous default rule allowing SSH access on TCP/22.
sudo firewall-cmd --permanent --add-port=5022/tcp
sudo firewall-cmd --permanent --remove-service=ssh
If you have a web server you may want to allow the following rules so your sites could be accessed over the internet.
sudo firewall-cmd --permanent --add-service=http
sudo firewall-cmd --permanent --add-service=https
You can use this for similar rules related to any systems you want to be publicly accessible. This test server is setup to host a website and email services, so in addition to the updated SSH and HTTP(S) rules, additional rules for secure POP3, IMAP, and SMTP have been added.
sudo firewall-cmd --permanent --add-service=pop3s
sudo firewall-cmd --permanent --add-service=imaps
sudo firewall-cmd --permanent --add-service=smtp
In order for Firewalld to accept those settings you must restart the firewall.
sudo firewall-cmd --reload
Your settings will have been saved and you are ready to proceed.
To verify all the services/ports that are available run the following:
sudo firewall-cmd --permanent --list-all
This is the default page after configuring the Firewalld rules on a CentOS 7 server
NTP Time Sync
The NTP (Network Time Protocol) is a basically used to synchronize the time and date of computers over the network in order to remain accurate and up to date. Let us begin by installing the NTP(If it hasn’t been installed) and configuring the service to synchronize with their servers.
sudo yum install ntp
Once the NTP service is installed, we need to make sure that the service is ON.
sudo systemctl start ntpd
Now that the service has started lets enable the NTP server so that it will constantly update the server’s time from the NTP server.
sudo systemctl enable ntpd
Add Swap File
A Swap file is simply a small amount of space created on a servers hard drive to simulate Ram. In the event that the server is running low on memory it will look at the hard drive and ease the load tricking the system to think it has more memory. We will set up the swap file on the hard drive to increase the performance of the server just a little bit more.
Begin by checking your resources to make sure we can add the file. When you run the following command you will see the percentage space on your Hard drive that is currently being used.
When creating a Swap file usually you want to add half of your existing RAM up to 4GB(If you have 1GB of actual Ram then you add a 512MB file). In this part I will be adding a 512MB swap file to the drive. The way that this is calculated is by 1024 x 512MB = 524288 block size.
sudo dd if=/dev/zero of=/swapfile bs=1024 count=524288
Now that we have added a swap file, a Swap file area needs to be created in order to proceed.
sudo mkswap /swapfile
With the Swap file created and the Swap file area added we can go ahead and add permissions to the file so that only the owner can read and write.
sudo chown root:root /swapfile
sudo chmod 0600 /swapfile
Now that the swap file has the appropriate permissions we can go ahead and activate the it.
sudo swapon /swapfile
You can verify your newly added Swap file with the following.
sudo swapon -s
In order to make the Swap file always active even after a reboot, we must configure it accordingly.
sudo vi /etc/fstab
Paste the following command at the bottom of the file save your work and exit.
/swapfile swap swap defaults 0 0
Finally, verify if your swapfile is activated by typing the following command:
This is the default page after creating a Swap File on a CentOS 7 Server
With that, you now have a server with a strong security foundation which will give you the peace of mind knowing that your server is protected. You may now proceed building your platform according to your needs. Thank you for following along and feel free to check back with us for further updates.