WireGuard Server: Debian

In this tutorial, we setup a WireGuard service on a Debian server. This example uses “vanilla” Debian Buster.

At the end of this tutorial, the Debian server will have a virtual network interface wg0 living on private network 10.0.2.0/24. The Debian server will be ready to add WireGuard clients.

Platform

Install `sudo`

In this tutorial, we execute all commands as a non-root user with help from the sudo command. Debian doesn’t always come with sudo installed.

Check that sudo is installed.

$ sudo
-bash: sudo: command not found

In this example, the sudo command is missing. To fix, login as root, either via login prompt or via su - (which requires the root user password).

# apt install sudo
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
  sudo
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
...
Setting up sudo (1.8.27-1+deb10u1) ...
Processing triggers for man-db (2.8.5-2) ...
Processing triggers for systemd (241-7~deb10u2) ...

Enable `sudo`

By default, Debian does not allow non-root users to use the sudo command.

Check your non-root user. In this example, the non-root user is jacob. Login in as the non-root user and run groups.

$ groups
jacob cdrom floppy audio dip video plugdev netdev

If the sudo group is included in this list, then the non-root user can use sudo. In the above example, the group sudo does not appear. To fix, login as root, either via login prompt or via su - (which requires the root user password).

# adduser jacob sudo

Logout the root user. If su - was used to run adduser then also logout the non-root user. Login as the non-root user and run groups again.

$ groups
jacob cdrom floppy sudo audio dip video plugdev netdev

In the above example, the group sudo appears where it was missing before.

Setup WireGuard

Install WireGuard

Install the WireGuard packages. After this step, man wg and man wg-quick will work and the wg command gets bash completion.

$ sudo apt install wireguard --assume-yes
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  dkms linux-compiler-gcc-8-x86 linux-headers-4.19.0-16-amd64 linux-headers-4.19.0-16-common linux-headers-amd64 linux-kbuild-4.19 wireguard-dkms wireguard-tools
Suggested packages:
  python3-apport menu openresolv | resolvconf
The following NEW packages will be installed:
  dkms linux-compiler-gcc-8-x86 linux-headers-4.19.0-16-amd64 linux-headers-4.19.0-16-common linux-headers-amd64 linux-kbuild-4.19 wireguard wireguard-dkms wireguard-tools
0 upgraded, 9 newly installed, 0 to remove and 0 not upgraded.
...
DKMS: install completed.
Setting up wireguard-tools (1.0.20210223-1~bpo10+1) ...
wg-quick.target is a disabled or a static unit, not starting it.
Setting up linux-headers-4.19.0-16-common (4.19.181-1) ...
Setting up wireguard (1.0.20210223-1~bpo10+1) ...
Setting up linux-headers-4.19.0-16-amd64 (4.19.181-1) ...
Setting up linux-headers-amd64 (4.19+105+deb10u11) ...
Processing triggers for man-db (2.8.5-2) ...

Create Keys

In every client/server relationship, each peer has its own private and public keys. Create private and public keys for the WireGuard service. Protect the private key with a file mode creation mask.

$ (umask 077 && wg genkey > wg-private.key)
$ wg pubkey < wg-private.key > wg-public.key

Print the private key, we’ll need it soon.

$ cat wg-private.key
qPF9uU7qsCbw3uKR1t2Q0gfr2HasTKZGPkCHz2AszUs=

Create the WireGuard Network Device

Create the WireGuard service config file at /etc/wireguard/wg0.conf. (Use a command like sudo nano /etc/wireguard/wg0.conf.)

# define the WireGuard service
[Interface]

# contents of file wg-private.key that was recently created
PrivateKey = qPF9uU7qsCbw3uKR1t2Q0gfr2HasTKZGPkCHz2AszUs=

# UDP service port; 51820 is a common choice for WireGuard
ListenPort = 51820

Create the WireGuard network device at /etc/network/interfaces.d/wg0. (Use a command like sudo nano /etc/network/interfaces.d/wg0.)

# indicate that wg0 should be created when the system boots, and on ifup -a
auto wg0

# describe wg0 as an IPv4 interface with static address
iface wg0 inet static

        # static IP address 
        address 10.0.2.1/24

        # before ifup, create the device with this ip link command
        pre-up ip link add $IFACE type wireguard

        # before ifup, set the WireGuard config from earlier
        pre-up wg setconf $IFACE /etc/wireguard/$IFACE.conf

        # after ifdown, destroy the wg0 interface
        post-down ip link del $IFACE

Start WireGuard.

$ sudo ifup wg0

If this fails, then install package linux-headers-VERSION. It seems that the Debian WireGuard packages don’t declare that dependency, or it’s just broken in GCP.

$ sudo ifup wg0
RTNETLINK answers: Operation not supported
ifup: failed to bring up wg0

$ sudo apt install linux-headers-$(uname -r)
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following NEW packages will be installed:
...
Fetched 556 kB in 0s (7381 kB/s)                       
Selecting previously unselected package linux-headers-4.19.0-6-cloud-amd64.
(Reading database ... 60668 files and directories currently installed.)
Preparing to unpack .../linux-headers-4.19.0-6-cloud-amd64_4.19.67-2+deb10u2_amd64.deb ...
Unpacking linux-headers-4.19.0-6-cloud-amd64 (4.19.67-2+deb10u2) ...
Setting up linux-headers-4.19.0-6-cloud-amd64 (4.19.67-2+deb10u2) ...

$ sudo ifup wg0

At any time, verify that the WireGuard configuration for wg0 is what you expect:

$ sudo wg show wg0
interface: wg0
  public key: 2efuG9OYmMPQpbkJ8CVxGlvQflY6p1u+o4wjcgGII0A=
  private key: (hidden)
  listening port: 51820

At any time, verify that the wg0 network interface exists.

$ ip address show dev wg0
  7: wg0: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1420 qdisc noqueue state UNKNOWN group default qlen 1000
      link/none
      inet 10.0.2.1/24 brd 10.0.2.255 scope global wg0
         valid_lft forever preferred_lft forever