Hack for some dodgy DHCP leasing by dhcpd on an OpenBSD install.

check_ip_lease.sh

#!/bin/sh

######################################################################
# Check how many unique leases are defined in /var/db/dhcpd.leases
# If there are more leases than a specified number send an email
######################################################################

# Estimate how many IP address leases there are
NUM_LEASES=$(grep ^lease /var/db/dhcpd.leases | sort -rn | uniq | wc -l | tr -d ' ')

# Print out help/usage if there aren't enough parameters supplied
if [ $# -ne 2 ]
then
	echo "Usage: check_ip_leases.sh num email"
	echo "num - The number of leases you want to check for. If there are found to be more leases than the specified num then an alert is triggered."
	echo "email - Email address to send an alert to"
	echo "(There are currently $NUM_LEASES leases in use)"
	exit 0
fi

# Set the variables for the supplied parameters
CHECK_NUM=$1
EMAIL=$2

# Check if there are more leases than the specified parameter
if [[ $CHECK_NUM -lt $NUM_LEASES ]]
then
	# Too many leases so send an email alert
	echo "/var/db/dhcpd.leases has reached the IP leases threshold of $CHECK_NUM. There are currently $NUM_LEASES leases.\n\nTo fix this stop the DHCPD server, move /var/db/dhcpd.leases and then start the DHCPD server again." | mail -s "/var/db/dhcpd.leases IP leases limit reached!" $EMAIL
fi