Will send mail to root@localhost if disk usage on one or more file systems is above 80 percent

disk_free_check.rb

#! /usr/bin/ruby -w

require 'net/smtp'

# Configuration
SMTP_SERVER = "localhost"
FROM_ADDRESS = "root@localhost"
TO_ADDRESS  = "root@localhost"
DEFAULT_LIMIT = 80

# Warnlimit
WARN_LIMIT = ARGV[0].to_i > 0 ? ARGV[0].to_i : DEFAULT_LIMIT

# Parse data, making sure blocksize is 1024
df = `df -k`

# Report variable
report = []

# first line from report
df.each do |line|
  if line =~ /^([\w\/]+)\s+(\d+)\s+(\d+)\s+(\d+)\s+(\d+%)\s+(.+$)/

    device, blocks, used, avail, percentage, mountpoint = $1, $2, $3, $4, $5, $6
    if percentage.to_i > WARN_LIMIT
      report << {
        :device => device,
        :mountpoint => mountpoint,
        :percentage => percentage.to_i,
        :free_space => avail.to_i / 1024
      }
    end

  end
end

exit 0 if report.empty?

# Create report
subject = "[Warning] Running low on disk space: #{report.map { |hash| hash[:device] }.join(" ")}"

report.map! do |hash|
  "Device #{hash[:device]}, mounted on #{hash[:mountpoint]}: " +\
  "#{hash[:percentage]}% (#{hash[:free_space]}MB free)"
end
report = report.join("\n")

message = <<EOT
From: #{FROM_ADDRESS}
To: #{TO_ADDRESS}
Subject: #{subject}

Warning, we're currently running low on disk space on the following devices:

#{report}

Please take action as soon as possible to avoid potential data loss.
EOT

Net::SMTP.start(SMTP_SERVER) do |smtp|
  smtp.send_message message, FROM_ADDRESS, [TO_ADDRESS]
end