Bash script to automated Email Notification upon USB Device Connection

Last updated: Jun 26, 2023

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
- ssmtp: for sending emails

Installing and configuring ssmtp

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

Install ssmtp:

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

Edit /etc/ssmtp.conf:

#
# Config file for sSMTP sendmail
#
# The person who gets all mail for userids < 1000
# Make this empty to disable rewriting.
#root=postmaster

# The place where the mail goes. The actual machine name is required no 
# MX records are consulted. Commonly mailhosts are named mail.domain.com
mailhub=mail.std.rocks:465

# Where will the mail seem to come from?
#rewriteDomain=

# The full hostname
hostname=backup.std.local

# Are users allowed to set their own From: address?
# YES - Allow the user to specify their own From: address
# NO - Use the system generated From: address
#FromLineOverride=YES

root=root@backup.std.local
rewriteDomain=std.rocks

TLS_CA_FILE=/etc/ssl/certs/ca-certificates.crt
UseTLS=Yes
UseSTARTTLS=No

FromLineOverride=yes

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: $MAIL_ADDRESS" >> /tmp/mail_usb_disk.header
        echo "Date: "`/bin/date -R` >> /tmp/mail_usb_disk.header
        echo "Subject: Disk has been plugged in" >> /tmp/mail_usb_disk.header
        echo "Content-type: text/plain; charset=utf-8" >> /tmp/mail_usb_disk.header
        echo "" >> /tmp/mail_usb_disk.header
        echo "Disk has been plugged in" >> /tmp/mail_usb_disk.header
        cat /tmp/mail_usb_disk.header | /usr/sbin/sendmail -f "$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

Computing

Music

Misc

Bash script to automated Email Notification upon USB Device Connection

Installing and configuring ssmtp

udev

Bash script