Update Linux WireGuard client instructions (#1407)

docs/client-linux-wireguard.md

@@ -2,38 +2,54 @@
 
 ## Install WireGuard
 
-To connect to your Algo VPN using [WireGuard](https://www.wireguard.com) from an Ubuntu Server 16.04 (Xenial) or 18.04 (Bionic) client, first install WireGuard on the client:
+To connect to your AlgoVPN using [WireGuard](https://www.wireguard.com) from Ubuntu Server, first install WireGuard:
 
 ```shell
 # Add the WireGuard repository:
 sudo add-apt-repository ppa:wireguard/wireguard
 
-# Update the list of available packages (not necessary on Bionic):
+# Update the list of available packages (not necessary on Bionic or later):
 sudo apt update 
 
 # Install the tools and kernel module:
 sudo apt install wireguard
 ```
 
-(For installation on other Linux distributions, see the [Installation](https://www.wireguard.com/install/) page on the WireGuard site.)
+For installation on other Linux distributions, see the [Installation](https://www.wireguard.com/install/) page on the WireGuard site.
 
 ## Locate the Config File
 
-The Algo-generated config files for WireGuard are named `configs/<ip_address>/wireguard/<username>.conf` on the system where you ran `./algo`. One file was generated for each of the users you added to `config.cfg` before you ran `./algo`. Each Linux and Android client you connect to your Algo VPN must use a different WireGuard config file. Choose one of these files and copy it to your Linux client.
+The Algo-generated config files for WireGuard are named `configs/<ip_address>/wireguard/<username>.conf` on the system where you ran `./algo`. One file was generated for each of the users you added to `config.cfg`. Each WireGuard client you connect to your AlgoVPN must use a different config file. Choose one of these files and copy it to your Linux client.
 
-If your client is running Bionic (or another Linux that uses `systemd-resolved` for DNS) you should first edit the config file. Comment out the line that begins with `DNS =` and replace it with:
+## Configure DNS
+
+### Ubuntu 18.04 (Bionic)
+
+If your client is running Bionic (or another Linux that uses `systemd-resolved` for DNS but does not have `resolvectl` or `resolvconf` installed) you should first edit the config file. Comment out the line that begins with `DNS =` and replace it with:
 ```
 PostUp = systemd-resolve -i %i --set-dns=172.16.0.1 --set-domain=~.
 ```
 Use the IP address shown on the `DNS =` line (for most, this will be `172.16.0.1`). If the `DNS =` line contains multiple IP addresses, use multiple  `--set-dns=` options.
 
+### Ubuntu 18.10 (Cosmic) or 19.04 (Disco)
+
+If your client is running Cosmic or Disco (or another Linux that uses `systemd-resolved` for DNS and has `resolvectl` but *not* `resolvconf` installed) you can either edit the config file as shown above for Bionic or run the following command once:
+
+```
+sudo ln -s /usr/bin/resolvectl /usr/bin/resolvconf
+```
+
+### Other Linux Distributions
+
+On other Linux distributions you might need to install the `openresolv` package.
+
 ## Configure WireGuard
 
 Finally, install the config file on your client as `/etc/wireguard/wg0.conf` and start WireGuard:
 
 ```shell
 # Install the config file to the WireGuard configuration directory on your
-# Bionic or Xenial client:
+# Linux client:
 sudo install -o root -g root -m 600 <username>.conf /etc/wireguard/wg0.conf
 
 # Start the WireGuard VPN:
@@ -42,14 +58,14 @@ sudo systemctl start wg-quick@wg0
 # Check that it started properly:
 sudo systemctl status wg-quick@wg0
 
-# Verify the connection to the Algo VPN:
+# Verify the connection to the AlgoVPN:
 sudo wg
 
-# See that your client is using the IP address of your Algo VPN:
+# See that your client is using the IP address of your AlgoVPN:
 curl ipv4.icanhazip.com
 
 # Optionally configure the connection to come up at boot time:
 sudo systemctl enable wg-quick@wg0
 ```
 
-(If your Linux distribution does not use `systemd`, you can bring up WireGuard with `sudo wg-quick up wg0`).
+If your Linux distribution does not use `systemd` you can bring up WireGuard with `sudo wg-quick up wg0`.