Fail2ban

Skill ComeOnOliver/skillshub/skills/TerminalSkills/skills/fail2ban

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Install

npx -y skills add ComeOnOliver/skillshub --skill fail2ban

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SKILL.md

1.3 KB, 366 tokens by cl100k_base, as published. Nobody here has run it

Fail2Ban

Overview

Fail2Ban monitors log files for failed authentication attempts and bans offending IPs using iptables/nftables. Protects SSH, Nginx, Apache, Postfix, and any service with log-based authentication.

Instructions

Step 1: Install

sudo apt install fail2ban
sudo systemctl enable fail2ban

Step 2: Configure

# /etc/fail2ban/jail.local — Custom configuration (never edit jail.conf)
[DEFAULT]
bantime = 1h
findtime = 10m
maxretry = 5
banaction = iptables-multiport

[sshd]
enabled = true
port = ssh
maxretry = 3
bantime = 24h

[nginx-http-auth]
enabled = true
port = http,https
maxretry = 5

[nginx-botsearch]
enabled = true
port = http,https
maxretry = 2
bantime = 7d

Step 3: Monitor

sudo fail2ban-client status               # list active jails
sudo fail2ban-client status sshd           # show banned IPs
sudo fail2ban-client set sshd unbanip 1.2.3.4   # unban
sudo fail2ban-client set sshd banip 5.6.7.8     # manual ban

Guidelines

Always create jail.local — jail.conf gets overwritten on updates.
Start conservative: 5 retries, 1h ban. Adjust based on logs.
For modern alternative with community threat sharing, consider CrowdSec.
Use fail2ban-regex to test custom filters before deploying.

What ships with it

Read from the repository

Just SKILL.md. No reference files, no scripts.