Pure-FTPd is a free open-source FTP server designed with security in mind. In this tutorial, we are going to take a look at how to set up a secure FTP server on Ubuntu server with Pure-FTPd and how to enforce TLS encryption.

Note: This tutorial works on all current Ubuntu releases, including Ubuntu 22.04, 20.04, and 18.04.

Pure-FTPd Features:

• It supports SSL/TLS encryption and thus passwords and commands can be protected.
• It can run on most Unix-like systems: Linux, BSDs, Solaris, Darwin, HPUX, AIX, and even iPhone.
• Available in 21 languages.
• Allows you to monitor active sessions.
• Supports a virtual quota system.
• And much more

For a complete list of features, please go to Pure-FTPd official website.

Step 1: Install Pure-FTPd on Ubuntu Server

It’s in the software repository, so issue the following command to install the FTP server.

sudo apt install pure-ftpd

Once installed, Pure-FTPd will be automatically started, as can be seen with this command:

systemctl status pure-ftpd

Output:

● pure-ftpd.service
   Loaded: loaded (/etc/init.d/pure-ftpd; bad; vendor preset: enabled)
   Active: active (running) since Mon 2016-12-12 21:51:46 EST; 23s ago
     Docs: man:systemd-sysv-generator(8)
   CGroup: /system.slice/pure-ftpd.service
           └─3435 pure-ftpd (SERVER)

preset: enabled indicates it will auto-start at system boot time. If it’s not running, star it with:

sudo systemctl start pure-ftpd

And it’s listening on TCP port 21, which is the control port, as can be seen with

sudo ss -lnpt | grep pure-ftpd

Anonymous access is disabled by default. From now on you can use your system account to login, but plain text FTP is insecure and strongly discouraged. To have a secure FTP server, we need to encrypt communication with TLS.

Step 2: Enforce TLS Encryption

To enable both plain-text and TLS encryption, run the following command, which create the /etc/pure-ftpd/conf/TLS file and put number 1 into the file.

echo 1 | sudo tee /etc/pure-ftpd/conf/TLS

But it’s recommended to disable plain-text and use TLS encryption only, so put the number 2 to the file instead.

echo 2 | sudo tee /etc/pure-ftpd/conf/TLS

Now we enforced TLS, we need to obtain a valid TLS certificate. A self-signed certificate is not recommended because users will see warning like the screenshot below.

Step 3: Obtain a Trusted TLS Certificate from Let’s Encrypt

Run the following command to install Let’s Encrypt client (certbot) from the default Ubuntu repository.

sudo apt install certbot

I recommend using the standalone or webroot plugin to obtain TLS certificate for Pure-FTPd.

Standalone Plugin

If there’s no web server running on your Ubuntu server, you can use the standalone plugin. Run the following command. Don’t forget to set DNS A record for your sub-domain.

sudo certbot certonly --standalone --preferred-challenges http --agree-tos --email [email protected] -d ftp.example.com

Where:

• certonly: Obtain a certificate but don’t install it.
• --standalone: Use the standalone plugin to obtain a certificate
• --preferred-challenges http: Perform http-01 challenge to validate our domain, which will use port 80.
• --agree-tos: Agree to Let’s Encrypt terms of service.
• --email: Email address is used for account registration and recovery.
• -d: Specify your domain name.

As you can see from the following screenshot, I successfully obtained the certificate.

Using webroot Plugin

If your Ubuntu server has a web server, then it’s a good idea to use the webroot plugin to obtain a certificate because the webroot plugin works with pretty much every web server and we don’t need to install the certificate in the web server.

First, you need to create a virtual host for ftp.example.com.

Apache

If you are using Apache, then

sudo nano /etc/apache2/sites-available/ftp.example.com.conf

And paste the following lines into the file.

<VirtualHost *:80>        
        ServerName ftp.example.com

        DocumentRoot /var/www/Pure-FTPd
</VirtualHost>

Save and close the file. Then create the web root directory.

sudo mkdir /var/www/Pure-FTPd

Set www-data (Apache user) as the owner of the web root.

sudo chown www-data:www-data /var/www/Pure-FTPd -R

Enable this virtual host.

sudo a2ensite ftp.example.com

Reload Apache for the changes to take effect.

sudo systemctl reload apache2

Once virtual host is created and enabled, run the following command to obtain Let’s Encrypt certificate using webroot plugin.

sudo certbot certonly --webroot --agree-tos --email [email protected] -d ftp.example.com -w /var/www/Pure-FTPd

Nginx

If you are using Nginx, then

sudo nano /etc/nginx/conf.d/ftp.example.com.conf

Paste the following lines into the file.

server {
      listen 80;
      listen [::]:80;
      server_name ftp.example.com;

      root /var/www/Pure-FTPd/;

      location ~ /.well-known/acme-challenge {
         allow all;
      }
}

Save and close the file. Then create the web root directory.

sudo mkdir -p /var/www/Pure-FTPd

Set www-data (Nginx user) as the owner of the web root.

sudo chown www-data:www-data /var/www/Pure-FTPd -R

Reload Nginx for the changes to take effect.

sudo systemctl reload nginx

Once virtual host is created and enabled, run the following command to obtain Let’s Encrypt certificate using webroot plugin.

sudo certbot certonly --webroot --agree-tos --email [email protected] -d ftp.example.com -w /var/www/Pure-FTPd

Step 4: Install the Certificate

Pure-FTPd requires that the certificate and private key are combined into one file named pure-ftpd.pem and stored under /etc/ssl/private/ directory.

Change to the /etc/letsencrypt/live/ftp.example.com/ directory.

cd /etc/letsencrypt/live/ftp.example.com/

You can use cat command to combine two files into one like below.

sudo cat fullchain.pem privkey.pem | sudo tee /etc/ssl/private/pure-ftpd.pem

Make sure only the root user can read the file.

sudo chmod 600 /etc/ssl/private/pure-ftpd.pem

we need to generate the Diffie-Hellman parameter with:

sudo openssl dhparam -out /etc/ssl/private/pure-ftpd-dhparams.pem 4096

If your server has a single CPU core, then this is going to take a long time (about 10 minutes).

Once that’s done, restart Pure-FTPd.

sudo systemctl restart pure-ftpd

Check the status to see if it’s running.

systemctl status pure-ftpd

Now you can connect to your FTP server over TLS.

Step 5: Using FTP Client

Nautilus File Manager on Ubuntu Desktop

If you use the Nautilus file manager to connect to FTP server via plain text ftp:// protocol

The connection will be refused.

Instead of ftp://, you must use ftps://. By default, FTP users will be brought to the / root directory on the server.

Filezilla FTP Client

Filezilla download link: https://filezilla-project.org/download.php?type=client

In Filezilla, you can use the SFTP protocol (FTP over SSH)

• sftp://ftp.example.com   port 22

or use the FTPES protocol (FTP over explicit TLS)

• ftpes://ftp.example.com  port 21

Please note that Filezilla doesn’t trust any certificate (self-signed or CA-signed) by default. Users must choose to trust certificate for themselves.

FileZilla Unknown Certificate Warning

Set Default Directory (SFTP)

If you use the SFTP protocol, you can change the default directory for FTP login.

Edit the SSH server configuration file.

sudo nano /etc/ssh/sshd_config

Find the following line.

Subsystem sftp /usr/lib/openssh/sftp-server

Change it to:

Subsystem sftp internal-sftp

Then add the following lines at the end of this file.

Match User username
        ChrootDirectory /
        ForceCommand internal-sftp -d /var/www/html/

In the above lines, I set the default directory to /var/www/html/, so when the user logs in over SFTP, the default directory would be set to /var/www/html/.  You need to change the username to your real username.

Save and close the file. Then restart SSH server.

sudo systemctl restart ssh

Auto-Renew TLS Certificate

You can create Cron job to automatically renew TLS certificate. Simply open root user’s crontab file.

sudo crontab -e

Add the following line at the bottom of the file.

@daily certbot renew --quiet && cd /etc/letsencrypt/live/ftp.example.com/ && cat fullchain.pem privkey.pem | tee /etc/ssl/private/pure-ftpd.pem && systemctl restart pure-ftpd

It’s necessary to reload pure-ftpd to make it pick up the new certificate and private key.

Wrapping Up

I hope this tutorial helped you set up a secure FTP server with Pure-FTPd on Ubuntu. As always, if you found this post useful, then subscribe to our free newsletter. You can also follow us on Twitter or like our Facebook page.

You may also want to set up SSH passwordless login.

• 2 Simple Steps to Set up Passwordless SSH Login on Ubuntu

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• Set Up SSH Two-Factor Authentication (2FA) on Ubuntu 22.04/20.04 Server