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How To Set Up an NFS Server Using Block Storage

Published on November 1, 2022
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By Alex Garnett
Senior DevOps Technical Writer
How To Set Up an NFS Server Using Block Storage

Introduction

NFS, or Network File System, is a distributed file system protocol that allows you to mount remote directories on your server. This allows you to manage storage space in a different location and write to that space from multiple clients. NFS provides a relatively standard and performant way to access remote systems over a network and works well in situations where the shared resources must be accessed regularly.

Block storage is a generic term used to describe network-based storage volumes that are usually offered by hosting providers. Unlike Object Storage, block storage usually does not provide its own API for direct access. Instead, it needs to be mounted to an existing server and shared from that server. If you are using DigitalOcean’s Block Storage, running an NFS server on an attached droplet is a good solution to expose a block storage volume.

In this guide, you’ll go over how to install the software needed to host an NFS server, configure two NFS mounts on a server and client, and mount and unmount the remote shares.

Prerequisites

You will use two servers in this tutorial, with one sharing part of its filesystem with the other. To follow along, you will need:

  • Two Ubuntu servers. This tutorial will follow our best practices for Ubuntu 22.04, but most recent Ubuntu or Debian releases should also work. Each of these should have a non-root user with sudo privileges, a firewall set up with UFW, and private networking, if it’s available to you.

    • For assistance setting up a non-root user with sudo privileges and a firewall, follow our Initial Server Setup with Ubuntu 22.04 guide.

    • If you’re using DigitalOcean Droplets for your server and client, you can read more about setting up a private network in our documentation on How to Create a VPC. DigitalOcean droplets created since 2019 will automatically have a private network interface enabled.

Throughout this tutorial, the server that shares its directories will be referred to as the host and the server that mounts these directories as the client. The host server should have a block storage volume attached to it. If you are using DigitalOcean block storage, you can follow the documentation for creating and mounting a volume. You will also need to know the IP address for both servers. Other than when initially connecting over SSH, be sure to use the private network address, if available.

Throughout this tutorial these IP addresses will be referred to by the placeholders host_ip and client_ip. Please substitute as needed.

Step 1 — Downloading and Installing the Components

You’ll begin by installing the necessary components on each server.

On the Host

On the host server, install the nfs-kernel-server package, which will allow you to share your directories. Since this is the first operation that you’re performing with apt in this session, refresh your local package index before the installation:

  1. sudo apt update
  2. sudo apt install nfs-kernel-server

Once these packages are installed, switch to the client server.

On the Client

On the client server, you need to install a package called nfs-common, which provides NFS functionality without including any server components. Again, refresh the local package index prior to installation to ensure that you have up-to-date information:

  1. sudo apt update
  2. sudo apt install nfs-common

Note: It is also possible to connect to NFS shares on other platforms such as Windows or macOS by using built-in OS functionality. The nfs-common example is for Ubuntu servers.

Now that both servers have the necessary packages, you can start configuring them.

Step 2 — Creating the Share Directories on the Host

In this tutorial, you’ll create a general-purpose NFS mount that uses default NFS behavior to make it difficult for a user with root privileges on the client machine to interact with the host using those client superuser privileges. You might use something like this to store files which were uploaded using a content management system or to create space for users to easily share project files.

Assuming your block storage is mounted to your host at a path like /mnt/volume-nyc3-01, you can make a directory to share within that volume called nfs.

First, make the share directory:

  1. sudo mkdir -p /mnt/volume-nyc3-01/nfs

Since you’re creating it with sudo, the directory is owned by the host’s root user:

  1. ls -dl /mnt/volume-nyc3-01/nfs/
Output
drwxr-xr-x 2 root root 4096 Sep 27 16:19 /mnt/volume-nyc3-01/nfs/

NFS will translate any root operations on the client to the nobody:nogroup credentials as a security measure. Therefore, you need to change the directory ownership to match those credentials.

  1. sudo chown nobody:nogroup /mnt/volume-nyc3-01/nfs/

You’re now ready to export this directory.

Step 3 — Configuring the NFS Exports on the Host Server

Next, you’ll dive into the NFS configuration file to set up the sharing of these resources.

On the host machine, open the /etc/exports file in nano or your preferred text editor with root privileges:

  1. sudo nano /etc/exports

The file has comments showing the general structure of each configuration line. The syntax is as follows:

/etc/exports
directory_to_share    client(share_option1,...,share_optionN)

You’ll need to create a line for each of the directories that you plan to share. Be sure to change the client_ip placeholder shown here to your actual IP address:

/etc/exports
/mnt/volume-nyc3-01/nfs/    client_ip(rw,sync,no_subtree_check)

Here, you’re using the same configuration options for both directories with the exception of no_root_squash. Take a look at what each of these options mean:

  • rw: This option gives the client computer both read and write access to the volume.
  • sync: This option forces NFS to write changes to disk before replying. This results in a more stable and consistent environment since the reply reflects the actual state of the remote volume. However, it also reduces the speed of file operations.
  • no_subtree_check: This option prevents subtree checking, which is a process where the host must check whether the file is actually still available in the exported tree for every request. This can cause many problems when a file is renamed while the client has it opened. In almost all cases, it is better to disable subtree checking.
  • no_root_squash: By default, NFS translates requests from a root user remotely into a non-privileged user on the server. This was intended as security feature to prevent a root account on the client from using the file system of the host as root. no_root_squash disables this behavior for certain shares.

When you are finished making your changes, save and close the file. If you are using nano, press Ctrl+X, then when prompted, Y and then Enter. Then, to make the share available to the clients that you configured, restart the NFS server with the following command:

  1. sudo systemctl restart nfs-kernel-server

Before you can actually use the new share, however, you’ll need to be sure that traffic to the share is permitted by firewall rules.

Step 4 — Adjusting the Firewall on the Host

First, check the firewall status to see if it’s enabled and, if so, to see what’s currently permitted:

  1. sudo ufw status
Output
Status: active To Action From -- ------ ---- OpenSSH ALLOW Anywhere OpenSSH (v6) ALLOW Anywhere (v6)

On your system, only SSH traffic is being allowed through, so you’ll need to add a rule for NFS traffic.

With many applications, you can use sudo ufw app list and enable them by name, but nfs is not one of those. However, because ufw also checks /etc/services for the port and protocol of a service, you can still add NFS by name. Best practice recommends that you enable the most restrictive rule that will still allow the traffic you want to permit, so rather than enabling traffic from just anywhere, you’ll be specific.

Use the following command to open port 2049 on the host, being sure to substitute your client IP address:

  1. sudo ufw allow from client_ip to any port nfs

You can verify the change by typing:

  1. sudo ufw status

You should see traffic allowed from port 2049 in the output:

Output
Status: active To Action From -- ------ ---- OpenSSH ALLOW Anywhere 2049 ALLOW 203.0.113.24 OpenSSH (v6) ALLOW Anywhere (v6)

This confirms that UFW will only allow NFS traffic on port 2049 from your client machine.

Step 5 — Creating Mount Points and Mounting Directories on the Client

Now that the host server is configured and serving its share, you’ll prepare your client.

In order to make the remote share available on the client, you need to mount the directory on the host that you want to share to an empty directory on the client.

Note: If there are files and directories in the folder that you use as a mount point, they will become hidden as soon as you mount the NFS share. To avoid the loss of important files, be sure that if you mount in a directory that already exists, the directory is empty.

Create a directory for your mounts:

  1. sudo mkdir -p /nfs/general

Now that you have a location to put the remote share and you’ve opened the firewall, you can mount the share using the IP address of your host server:

  1. sudo mount host_ip:/mnt/volume-nyc3-01/nfs/ /nfs/general

This commands will mount the share from the host computer onto the client machine. You can double-check that it mounted successfully in several ways. You can check this with a mount or findmnt command, but df -h provides a more readable output:

  1. df -h
Output
Filesystem Size Used Avail Use% Mounted on tmpfs 198M 972K 197M 1% /run /dev/vda1 50G 3.5G 47G 7% / tmpfs 989M 0 989M 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock /dev/vda15 105M 5.3M 100M 5% /boot/efi tmpfs 198M 4.0K 198M 1% /run/user/1000 10.124.0.3:/mnt/volume-nyc3-01/nfs/ 25G 5.9G 19G 24% /nfs/general

The share you mounted appears at the bottom. To see how much space is actually being used under each mount point, use the disk usage command du and the path of the mount. The -s flag provides a summary of usage rather than displaying the usage for every file. The -h prints human-readable output.

For example:

  1. du -sh /nfs/general
Output
4.0K /nfs/general

This shows us that the contents of the entire home directory is using only 4K of the available space.

Step 6 — Testing NFS Access

Next, test access to the share by writing something to it.

First, write a test file to the /mnt/volume-nyc3-01/nfs/ share:

  1. sudo touch /nfs/general/test

Then, check its ownership:

  1. ls -l /nfs/general/test
Output
-rw-r--r-- 1 nobody nogroup 0 Sep 28 18:05 /nfs/general/test

Because you mounted this volume without changing NFS’s default behavior and created the file as the client machine’s root user via the sudo command, ownership of the file defaults to nobody:nogroup. client superusers won’t be able to perform typical administrative actions, like changing the owner of a file or creating a new directory for a group of users, on this NFS-mounted share.

Step 7 — Mounting the Remote NFS Directories at Boot

You can mount the remote NFS share automatically at boot by adding them to /etc/fstab file on the client.

Open this file with root privileges in your text editor:

  1. sudo nano /etc/fstab

At the bottom of the file, add a line for each of your shares. They will look like this:

/etc/fstab
. . .
host_ip:/mnt/volume-nyc3-01/nfs/    /nfs/general   nfs auto,nofail,noatime,nolock,intr,tcp,actimeo=1800 0 0

Note: You can find more information about the options you are specifying here in the NFS man page. You can access this by running the following command:

  1. man nfs

The client will automatically mount remote partitions at boot, although it may take a few moments to establish the connection and for the shares to be available.

Step 8 — Unmounting an NFS Remote Share

If you no longer want a remote directory to be mounted on your system, you can unmount it by moving out of the share’s directory structure and unmounting, like this:

  1. cd ~
  2. sudo umount /nfs/general

Take note that the command is named umount not unmount as you may expect.

This will remove remote shares, leaving only your local storage accessible:

  1. df -h
Output
Filesystem Size Used Avail Use% Mounted on tmpfs 198M 972K 197M 1% /run /dev/vda1 50G 3.5G 47G 7% / tmpfs 989M 0 989M 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock /dev/vda15 105M 5.3M 100M 5% /boot/efi tmpfs 198M 4.0K 198M 1% /run/user/1000

If you also want to prevent them from being remounted on the next reboot, edit /etc/fstab and either delete the line or comment it out by placing a # character at the beginning of the line. You can also prevent auto-mounting by removing the auto option, which will allow you to still mount it manually.

Conclusion

In this tutorial, you created an NFS host and illustrated some key NFS behaviors by creating an NFS mount, which you shared with a NFS client.

If you’re looking to implement NFS in production, it’s important to note that the protocol itself is not encrypted. In cases where you’re sharing over a private network, this may not be a problem. In other cases, a VPN or some other type of encrypted tunnel will be necessary to protect your data.

If you’ve enjoyed this tutorial and our broader community, consider checking out our DigitalOcean products which can also help you achieve your development goals.

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