Knowledgebase

Introduction

When you first create a new Debian 9 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.

Step One — Logging in as Root

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 guide on how to connect to your server  with SSH, which covers this process in detail.

If you are not already connected to your server, go ahead and log in as the root user 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.

About Root

The root user is the administrative user in a Linux environment that 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.

The next step is to set up an alternative user account with a reduced scope of influence for day-to-day work. We'll teach you how to gain increased privileges during the times when you need them.

Step Two — Creating a New User

Once you are logged in as root, we're prepared to add the new user account that we will use to log in from now on.

Note: In some environments, a package called unscd may be installed by default in order to speed up requests to name servers like LDAP. The most recent version currently available in Debian contains a bug that causes certain commands (like the adduser command below) to produce additional output that looks like this:

sent invalidate(passwd) request, exiting
sent invalidate(group) request, exiting

These messages are harmless, but if you wish to avoid them, it is safe to remove the unscd package if you do not not plan on using systems like LDAP for user information:

• apt remove unscd

This example creates a new user called sammy, but you should replace it with a username that you like:

• adduser sammy

You will be asked a few questions, starting with the account password.

Enter a strong password and, optionally, fill in any of the additional information if you would like. This is not required and you can just hit ENTER in any field you wish to skip.

Step Three — Granting Administrative Privileges

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 sudo group. By default, on Debian 9, users who belong to the sudo group are allowed to use the sudo command.

As root, run this command to add your new user to the sudo group (substitute the highlighted word with your new user):

• usermod -aG sudo sammy

Now, when logged in as your regular user, you can type sudo before commands to perform actions with superuser privileges.

Step Four — Setting Up a Basic Firewall

Debian servers can use firewalls to make sure only connections to certain services are allowed. Although the iptables firewall is installed by default, Debian does not strongly recommend any specific firewall. In this guide, we will install and use the UFW firewall to help set policies and manage exceptions.

We can use the apt package manager to install UFW. Update the local index to retrieve the latest information about available packages and then install the firewall by typing:

• apt update
• apt install ufw

You can see this by typing:

• ufw app list

Available applications:
  . . .
  OpenSSH
  . . .

We need to make sure that the firewall allows SSH connections so that we can log back in next time. We can allow these connections by typing:

• ufw allow OpenSSH

Afterwards, we can enable the firewall by typing:

• ufw enable

Type "y" and press ENTER to proceed. You can see that SSH connections are still allowed by typing:

• ufw status

Status: active

To                         Action      From
--                         ------      ----
OpenSSH                    ALLOW       Anywhere
OpenSSH (v6)               ALLOW       Anywhere (v6)

As the firewall is currently blocking all connections except for SSH, if you install and configure additional services, you will need to adjust the firewall settings to allow acceptable traffic in. You can learn some common UFW operations in this guide.

Step Five — Enabling External Access for Your Regular User

Now that we have a regular user for daily use, we need to make sure we can SSH into the account directly.

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 the Root Account Uses Password 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 Debian 9 to learn how to configure key-based authentication.

If the Root Account Uses SSH Key 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 local 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 in our existing session with the cp command. Afterwards, we can adjust ownership of the files using the chown command.

Make sure to change the highlighted portions of the command below to match your regular user's name:

• cp -r ~/.ssh /home/sammy
• chown -R sammy:sammy /home/sammy/.ssh

Now, open up a new terminal session and using SSH with your new username:

• 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).

Step Six — Completing Optional Configuration

Now that we have a strong baseline configuration, we can consider a few optional steps to make the system more accessible. The following sections cover a few additional tweaks focused on usability.

Installing man Pages

Debian provides extensive manuals for most software in the form of man pages. However, the man command is not always included by default on minimal installations.

Install the man-db package to install the man command and the manual databases:

• sudo apt install man-db

Now, to view the manual for a component, you can type:

• man command

For example, to view the manual for the top command, type:

• man top

Most packages in the Debian repositories include manual pages as part of their installation.

Changing the Default Editor

Debian offers a wide variety of text editors, some of which are included in the base system. Commands with integrated editor support, like visudo and systemctl edit, pass text to the editor command, which is mapped to the system default editor. Setting the default editor according to your preferences can help you configure your system more easily and avoid frustration.

If your preferred editor is not installed by default, use apt to install it first:

• sudo apt install your_preferred_editor

Next, you can view the current default and modify the selection using the update-alternatives command:

• sudo update-alternatives --config editor

The command displays a table of the editors it knows about with a prompt to change the default:

There are 8 choices for the alternative editor (providing /usr/bin/editor).

  Selection    Path                Priority   Status
------------------------------------------------------------
* 0            /usr/bin/joe         70        auto mode
  1            /bin/nano            40        manual mode
  2            /usr/bin/jmacs       50        manual mode
  3            /usr/bin/joe         70        manual mode
  4            /usr/bin/jpico       50        manual mode
  5            /usr/bin/jstar       50        manual mode
  6            /usr/bin/rjoe        25        manual mode
  7            /usr/bin/vim.basic   30        manual mode
  8            /usr/bin/vim.tiny    15        manual mode

Press <enter> to keep the current choice[*], or type selection number:

The asterisk in the far left column indicates the current selection. To change the default, type the "Selection" number for your preferred editor and press Enter. For example, to use nano as the default editor given the above table, we would choose 1:

Press <enter> to keep the current choice[*], or type selection number: 1
update-alternatives: using /bin/nano to provide /usr/bin/editor (editor) in manual mode

From now on, your preferred editor will be used by commands like visudo and systemctl edit, or when the editor command is called.

Where To Go From Here?

At this point, you have a solid foundation for your server. You can install any of the software you need on your server now.