Email notification for fail2ban events

So I’ve configured my fail2ban installation and I’m also able to send emails. But wouldn’t it be awesome if I’ll get notified via email about any fail2ban event?

We start with editing the /etc/fail2ban/jail.local file. Look for the destemail and action parameters and change them accordingly:

mta = sendmail
destemail =
senderemail =
action = %(action_mwl)s

The action can be one of these, whereby I’ve chosen action_mwl:

  • action_: ban only the IP
  • action_mw: ban the IP and send email with whois information about the banned IP
  • action_mwl: ban the IP and send email with whois information about the banned IP and add relevant log lines to the email
  • action_cf_mwl: notify Cloudfare about the offending IP, ban the IP and send email with whois information about the banned IP

Do a restart of fail2ban:

sudo systemctl restart fail2ban

You’ll receive a lot of emails from fail2ban. This also includes any starts and stops of fail2ban as well as the ban notifications. You can limit this behavior by adding following content to the file /etc/fail2ban/action.d/mail-buffered.local:


# Option:  actionstart
# Notes.:  command executed once at the start of Fail2Ban.
# Values:  CMD
actionstart =

# Option:  actionstop
# Notes.:  command executed once at the end of Fail2Ban
# Values:  CMD
actionstop =

Now copy this file a few times with different file names:

sudo cp /etc/fail2ban/action.d/mail-buffered.local /etc/fail2ban/action.d/mail.local
sudo cp /etc/fail2ban/action.d/mail-buffered.local /etc/fail2ban/action.d/mail-whois-lines.local
sudo cp /etc/fail2ban/action.d/mail-buffered.local /etc/fail2ban/action.d/mail-whois.local
sudo cp /etc/fail2ban/action.d/mail-buffered.local /etc/fail2ban/action.d/sendmail-buffered.local
sudo cp /etc/fail2ban/action.d/mail-buffered.local /etc/fail2ban/action.d/sendmail-common.local

Do a restart of fail2ban:

sudo systemctl restart fail2ban

You should now only receive emails for ban events.

Protect SSH services with fail2ban

If you’ll open SSH on a server to the open internet, you’ll notice a lot of bots trying to login. You certainly should setup certificate based login, but banning offending IPs is also an important security measure.

I’ve installed fail2ban on my Raspbian installations and want to explain the installation and configuration. Its quite easy and the benefits are huge!

sudo apt-get install fail2ban

Create a copy of the original configuration file so that it won’t be overwritten by any updates:

sudo cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local

Search for a block for [default]. You should set:

bantime = 10m
findtime = 10m
maxretry = 5

These are the general settings. The settings for sshd should be a little bit stricter. Search a block for [sshd]. You should set:

enabled = true
maxretry = 3

You can enable and start fail2ban now using systemctl:

sudo systemctl enable fail2ban
sudo systemctl start fail2ban

Verify its up and running:

sudo systemctl status fail2ban.service
sudo fail2ban-client status
sudo fail2ban-client status sshd

If you end up being locked out, you can unlog an offending IP address using this command:

sudo fail2ban-client set sshd unbanip <offenders IP>

Banned connections will be dropped immediately by the firewall and should be visible with a “connection refused”.

Configure mail transport agent on Raspbian with external SMTP server

I want to get email notifications for actions on my Raspberry Pi using Raspbian. You could setup a separate mail server for that action but that seems to be a little bit overkill.

msmtp is a mail transfer agent which uses a configured smtp server for email transfer. This allows you to send emails via a configured smtp server (in my case from my webspace provider – by creating a new account using this link you’ll support the costs for running this blog).

Upgrade your raspbian:

sudo apt-get update && sudo apt-get upgrade

Install msmtp:

sudo apt-get install msmtp msmtp-mta mailutils

Get the location of the configuration files:

> msmtp --version
msmtp version 1.6.6
Platform: arm-unknown-linux-gnueabihf
TLS/SSL library: GnuTLS
Authentication library: GNU SASL
Supported authentication methods:
plain scram-sha-1 external gssapi cram-md5 digest-md5 login ntlm
IDN support: enabled
NLS: enabled, LOCALEDIR is /usr/share/locale
Keyring support: none
System configuration file name: /etc/msmtprc
User configuration file name: /home/pi/.msmtprc

Copyright (C) 2016 Martin Lambers and others.
This is free software.  You may redistribute copies of it under the terms of
the GNU General Public License <>.
There is NO WARRANTY, to the extent permitted by law.

Configure the system configuration:

sudo vi /etc/msmtprc

The content of my configuration file (note the necessary changes for servers and email addresses):

# Set default values for all following accounts.

# Use the mail submission port 587 instead of the SMTP port 25.
port 465

# Always use TLS.
tls on
tls_starttls off

# Set a list of trusted CAs for TLS. The default is to use system settings, but
# you can select your own file.
tls_trust_file /etc/ssl/certs/ca-certificates.crt

# If you select your own file, you should also use the tls_crl_file command to
# check for revoked certificates, but unfortunately getting revocation lists and
# keeping them up to date is not straightforward.
#tls_crl_file ~/.tls-crls

# Mail account
# TODO: Use your own mail address

# Host name of the SMTP server
# TODO: Use the host of your own mail account
host <your Username provided by KAS>

# As an alternative to tls_trust_file/tls_crl_file, you can use tls_fingerprint
# to pin a single certificate. You have to update the fingerprint when the
# server certificate changes, but an attacker cannot trick you into accepting
# a fraudulent certificate. Get the fingerprint with
# $ msmtp --serverinfo --tls --tls-certcheck=off --host=smtp.freemail.example
#tls_fingerprint 00:11:22:33:44:55:66:77:88:99:AA:BB:CC:DD:EE:FF:00:11:22:33

# Envelope-from address
# TODO: Use your own mail address

# Authentication. The password is given using one of five methods, see below.
auth on

# TODO: Use your own user name fpr the mail account
user <The username of the email account you use for sending emails>

# Password method 1: Add the password to the system keyring, and let msmtp get
# it automatically. To set the keyring password using Gnome's libsecret:
# $ secret-tool store --label=msmtp \
#   host smtp.freemail.example \
#   service smtp \
#   user joe.smith

# Password method 2: Store the password in an encrypted file, and tell msmtp
# which command to use to decrypt it. This is usually used with GnuPG, as in
# this example. Usually gpg-agent will ask once for the decryption password.
#passwordeval gpg2 --no-tty -q -d ~/.msmtp-password.gpg

# Password method 3: Store the password directly in this file. Usually it is not
# a good idea to store passwords in plain text files. If you do it anyway, at
# least make sure that this file can only be read by yourself.
# TODO: Use the password of your own mail account
password <The password of the email account you use for sending emails>

# Password method 4: Store the password in ~/.netrc. This method is probably not
# relevant anymore.

# Password method 5: Do not specify a password. Msmtp will then prompt you for
# it. This means you need to be able to type into a terminal when msmtp runs.

# Set a default account
# TODO: Use your own mail address
account default:

# Map local users to mail addresses (for crontab)
aliases /etc/aliases

This file contains a username and password. Therefore limit its access to only root:

sudo chmod 600 /etc/msmtprc

Duplicate the config file to ~/.msmtprc if you want to provide email configuration for your user as well.

Now configure the recipients for your systems users by setting the recipients in /etc/aliases. Make sure, that you don’t have trailing spaces behind the email addresses:


Let your computer now that msmtp should be used as replacement for sendmail by adding this content to /etc/mail.rc

set sendmail="/usr/bin/msmtp -t"

Test your configuration by sending an email from the terminal:

echo "Content of your mail" | mail -s "Subject"

Use DDNS with Synology DiskStation

I’ve recently upgraded my webspace to the PrivatPlus tariff. As part of this tariff I’m now able to use DDNS running under the Domains I’m able to manage.

Setting up DDNS in KAS is explained quite well. However, I did not see instructions on how to use these credentials on a Synology DiskStation OS. Luckily, somebody else did this already.

The important part was, that when you’ll need to customize a DDNS provider first before it can be setup in DiskStation settings.

  • Go to Control Panel, External Access and click on Customize
  • Add a new name for the DDNS provider, e.g.
  • Use this Query URL (for IPv4):
  • Now you can add a new DDNS entry
  • Select as provider
  • Enter the credentials as required
  • Enter the hostname you want to setup for DDNS
  • Click on “Test Connection”
  • The state should be “Normal”
  • Click on “OK”

Free purgeable space on MacOS Mojave

I’ve recently deleted a large preview database file for Lightroom and was happy about the 80GB won free space. However, the MacOS disk utility as well as the terminal command “df -h” did not show the free space. I’ve also checked the trash and cleared it, but there was no change in the available disk space.

I’ve taken a closer look at the free space column in the disk utility and found a new variable behind the available disk space: GB purgeable.

However, there is nowhere an option to purge this space. Upon further searching I’ve found this tip on stack overflow:

It looks like TimeMachine takes up a lot of free space in APFS snapshots which needs manual cleaning using this command:

tmutil thinlocalsnapshots / $((100 * 1024 * 1204 * 1024)) 4

This command tries to free 100GB space from the local snapshots. It’s using the highest priority (4) to speed up the cleaning.

After I’ve executed that command, the available free disk space was shown correctly again.