Add basic server instructions

content/en/administration/installation.md

@@ -5,20 +5,109 @@ menu:
     parent: administration
     weight: 1
 ---
-
 ## Basic server setup (optional)
 
-If you are setting up a fresh machine, it is recommended that you secure it first:
+If you are setting up a fresh machine, it is recommended that you secure it first. Assuming that you are running **Ubuntu 18.04**:
 
-- Do not allow password-based SSH login (keys only)
-- Update system packages
-- Install fail2ban so it blocks repeated login attempts
-- Install a firewall and only whitelist SSH, HTTP and HTTPS ports
+### Do not allow password-based SSH login (keys only)
+
+First make sure you are actually logging in to the server using keys and not via a password, otherwise this will lock you out. Many hosting providers support uploading a public key and automatically set up key-based root login on new machines for you.
+
+Edit `/etc/ssh/sshd_config` and find `PasswordAuthentication`. Make sure it's uncommented and set to `no`. If you made any changes, restart sshd:
+
+```sh
+systemctl restart ssh
+```
+
+### Update system packages
+
+```sh
+apt update && apt upgrade -y
+```
+
+### Install fail2ban so it blocks repeated login attempts
+
+```sh
+apt install fail2ban
+```
+
+Edit `/etc/fail2ban/jail.local` and put this inside:
+
+```ini
+[DEFAULT]
+destemail = your@email.here
+sendername = Fail2Ban
+
+[sshd]
+enabled = true
+port = 22
+
+[sshd-ddos]
+enabled = true
+port = 22
+```
+
+Finally restart fail2ban:
+
+```sh
+systemctl restart fail2ban
+```
+
+### Install a firewall and only whitelist SSH, HTTP and HTTPS ports
+
+First, install iptables-persistent. During installation it will ask you if you want to keep current rules--decline.
+
+```sh
+apt install -y iptables-persistent
+```
+
+Edit `/etc/iptables/rules.v4` and put this inside:
+
+```
+*filter
+
+#  Allow all loopback (lo0) traffic and drop all traffic to 127/8 that doesn't use lo0
+-A INPUT -i lo -j ACCEPT
+-A INPUT ! -i lo -d 127.0.0.0/8 -j REJECT
+
+#  Accept all established inbound connections
+-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
+
+#  Allow all outbound traffic - you can modify this to only allow certain traffic
+-A OUTPUT -j ACCEPT
+
+#  Allow HTTP and HTTPS connections from anywhere (the normal ports for websites and SSL).
+-A INPUT -p tcp --dport 80 -j ACCEPT
+-A INPUT -p tcp --dport 443 -j ACCEPT
+
+#  Allow SSH connections
+#  The -dport number should be the same port number you set in sshd_config
+-A INPUT -p tcp -m state --state NEW --dport 22 -j ACCEPT
+
+#  Allow ping
+-A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT
+
+#  Log iptables denied calls
+-A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7
+
+#  Reject all other inbound - default deny unless explicitly allowed policy
+-A INPUT -j REJECT
+-A FORWARD -j REJECT
+
+COMMIT
+```
+
+With iptables-persistent, that configuration will be loaded at boot time. But since we are not rebooting right now, we need to load it manually for the first time:
+
+```sh
+iptables-restore < /etc/iptables/rules.v4
+```
 
 ## Pre-requisites
 
-- A machine running Ubuntu 18.04 that you have root access to
-- A domain name (or a subdomain) for the Mastodon server
+- A machine running **Ubuntu 18.04** that you have root access to
+- A **domain name** (or a subdomain) for the Mastodon server, e.g. `example.com`
+- An e-mail delivery service or other **SMTP server**
 
 You will be running the commands as root. If you aren't already root, switch to root: