Bash script to automated Email Notification upon USB Device Connection

Last updated: May 1, 2024

On a Debian GNU/Linux system, I have worked on a solution to notify users via email when a USB hard disk drive is connected. The objective is to inform the system administrator that the USB drive is successfully connected.

To achieve this, I utilized the following:
- udev: a device manager that invokes a custom script
- msmtp: for sending emails

Installing and configuring msmtp

Example here with msmtp which will send emails to mail.std.rocks relay on the 465 SSL port.

Install msmtp:

root@host:~# apt update && apt install msmtp

Edit /etc/msmtprc:

account STD
#Mail Server :
host mail.std.rocks
port 465
from backup@std.rocks
#LOGIN / PASSWORD
user backup@std.rocks
password MyWeakPassword

auth on
tls on
tls_starttls on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
tls_certcheck off
logfile /var/log/msmtp.log

account default : STD

udev

udev is a device manager for GNU/Linux systems that dynamically manages devices and their corresponding device nodes in the system. It stands for "userspace device" and operates in the userspace rather than the kernel space. It will allow us to execute a script when a USB disk device will be plugged in.

Note: let's say the disk we want to monitor is /dev/sda

Just for information we can print all attributes of the /dev/sda device:

root@host:~# udevadm info --attribute-walk --path=$(udevadm info --query=path --name=/dev/sda)

Create a /etc/udev/rules.d/10_usb-disk.rules file:

ACTION=="add", SUBSYSTEM=="block", SUBSYSTEMS=="usb", RUN{program}+="/usr/local/sbin/mail_usb_disk.sh"

Reload the udev rules and configuration:

root@host:~# udevadm control --reload

Bash script

Create /usr/local/sbin/mail_usb_disk.sh file:

root@host:~# touch /usr/local/sbin/mail_usb_disk.sh && chmod +x /usr/local/sbin/mail_usb_disk.sh

Edit /usr/local/sbin/mail_usb_disk.sh file:

I've noticed that the script is executed twice when a USB device is plugged in. To prevent sending two emails, I create a /tmp/udev_time file and compare its creation time to the current date. If the time difference is greater than 10 seconds, the email will be sent.
Edit 2023/07/01: Haven't tested but some says that it could be resolved by adding ENV{DEVTYPE}=="usb_device" in the rule.

#! /bin/sh

MAIL_ADDRESS="backup@std.rocks"
DATE=$(/bin/date "+%Y-%m-%dT%H:%M:%S")

UDEV_TIME="$(/bin/date --date="$(stat /tmp/udev_time | grep Modif | sed 's/Modif.*: //')" +%s)" #get /tmp/udev_time creation time
touch /tmp/udev_time
CUR_TIME="$(/bin/date +%s)"

#difference between current time and /tmp/udev_time creation time
TIME_DIFF=$(( (CUR_TIME - UDEV_TIME) ))

#Function
mailto () {
        LANG=C
        rm -f /tmp/mail_usb_disk.header
        echo "From: $MAIL_ADDRESS" >> /tmp/mail_usb_disk.header
        echo "To: $MAIL_ADDRESS" >> /tmp/mail_usb_disk.header
        echo "Date: "`/bin/date -R` >> /tmp/mail_usb_disk.header
        echo "Subject: Disk has been plugged in" >> /tmp/mail_usb_disk.header
        echo "Content-type: text/plain; charset=utf-8" >> /tmp/mail_usb_disk.header
        echo "" >> /tmp/mail_usb_disk.header
        echo "Disk has been plugged in" >> /tmp/mail_usb_disk.header
        cat /tmp/mail_usb_disk.header | /usr/bin/msmtp -f "$MAIL_ADDRESS" "$MAIL_CLIENT"
        rm -f /tmp/mail_usb_disk.header
}

#Send email if time difference is greater than 10s
if [ "$TIME_DIFF" -gt 10 ]; then
	mailto
fi

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Bash script to automated Email Notification upon USB Device Connection

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