Fail2Ban Reference & Useful Commands

Category: All About Ubuntu
Last Updated: May 11, 2025
Applies To: Ubuntu Server 22.04+

Fail2Ban Jail Configuration

Fail2Ban jails control how long an IP remains banned after matching filters. To increase ban duration (e.g., to 48 hours):

Configuration File

sudo nano /etc/fail2ban/jail.local

Example Jail Settings for SSH and UFW Block:

[sshd]
enabled = true
port    = ssh
logpath = %(sshd_log)s
bantime = 172800
findtime = 600
maxretry = 3

[ufw-block]
enabled = true
filter  = ufw-block
logpath = /var/log/ufw.log
bantime = 172800
findtime = 600
maxretry = 3

✅ bantime is in seconds → 172800 equals 48 hours
✅ findtime is the window (in seconds) to detect repeated offenses
✅ maxretry is the number of failed attempts before banning

After changes:

sudo systemctl restart fail2ban

Useful Commands

Task	Command
Check fail2ban service status	sudo systemctl status fail2ban
Start fail2ban	sudo systemctl start fail2ban
Restart fail2ban	sudo systemctl restart fail2ban
View all jail statuses	sudo fail2ban-client status
View a specific jail (e.g., sshd)	sudo fail2ban-client status sshd
See currently banned IPs in a jail	sudo fail2ban-client get sshd banned
Unban an IP from a jail	sudo fail2ban-client set sshd unbanip <IP>
Get ignore list for a jail	sudo fail2ban-client get sshd ignoreip
Manually test a filter (dry run)	fail2ban-regex /var/log/auth.log /etc/fail2ban/filter.d/sshd.conf

Filter & Jail File Paths

File Purpose	Path
Jail configuration	/etc/fail2ban/jail.local
Custom filters	/etc/fail2ban/filter.d/
Fail2Ban main log	/var/log/fail2ban.log
UFW log (for ufw-block)	/var/log/ufw.log

Notes

• Use ignoreip to exempt safe IPs (including local/DDNS).

• Consider rotating logs weekly to avoid bloated logs.

• Fail2Ban can be extended to cover other services (Apache, Postfix, etc.).