A Nagios ruby NRPE plugin to check, list and graph all volumes for an Ubuntu server.

check_disk_usage.rb

#!/usr/bin/env ruby
# you may need to use /usr/bin/ruby

  def largest_hash_key(hash)
    hash.max_by{|k,v| v}
  end
   
    filesystem = %x(df -h)
  
    perfdata = filesystem.split("\n")
                     .grep(/\A\/dev/)
                     .map(&:split)
                     .map{ |e| "'%s'=%s" % [ e[-1], e[-2] ] }
                     .join(" ")
  
    volumes = Hash[perfdata.split(" ").map {|str| str.split("=")}]

    volumes = volumes.map{ |k, v| [k, v.to_i] }

    full_disk = largest_hash_key(volumes)

    pc_full = full_disk[1]
       
    message = "#{perfdata} | #{perfdata}" 

    if pc_full > 94
       puts "DISK CRITICAL - #{message}"
       exit 2
    elsif pc_full > 89
       puts "DISK WARNING - #{message}"
       exit 1
    else
       puts "DISK OK - #{message}"
       exit 0   
    end

Make the file check_disk_usage.rb executable with chmod +x and upload it to /usr/lib/nagios/plugins.

Add the following line to nrpe.cfg

command[check_disk_usage]=/usr/lib/nagios/plugins/check_disk_usage.rb

Add the service in services.cfg:

define service {
hostgroup_name check_disk_usage
service_description check_disk_usage
check_command check_nrpe_1arg!check_disk_usage
use generic-service,graphed-service
notification_interval 5
}

Add the hostgroup in hostgroups.cfg (or hosts.cfg if you don't use hostgroups)

define hostgroup {
hostgroup_name check_disk_usage
alias check_disk_usage
members server1,server2,server3
}

Test with
nagios@nagios-server:/home/me$ /usr/lib/nagios/plugins/check_nrpe -H client-server -c check_disk_usage
DISK OK - '/'=37% '/tmp'=1% '/srv'=63% '/backups'=80% | '/'=37% '/tmp'=1% '/srv'=63% '/backups'=80%