System Monitoring for home users.

I recently covered a system monitoring tool called icinga. Its features and capabilities are very powerful but may be overkill for a home network. In this post, i will show an alternate setup which will allow you to pull system information from networked linux machines and send then back to a central server.

Here is an overview of the pieces that make this work. We will connect to client machines over ssh, execute a local script that will retrieve system information and then send this information back to us on a custom port using netcat. I would also use a utility called expect to aid in automating everything. You can find out much more about expect from google or watch this excellent tutorial on hak5.

The script file will need to be copied to each client machine. Here are the contents of the script. Give this script file executable permissions with the chmod command. Its a modified version from this:

Filename would be sysstat.sh

#!/bin/bash
CPUTIME=$(ps -eo pcpu | awk 'NR>1' | awk '{tot=tot+$1} END {print tot}')
CPUCORES=$(cat /proc/cpuinfo | grep -c processor)
echo "
System Summary (collected on `date`)

 - CPU Cores             = `echo $CPUCORES`
 - CPU Usage (average)       = `echo $CPUTIME / $CPUCORES | bc`%
 - Memory free (real)        = `free -m | head -n 2 | tail -n 1 | awk {'print $4'}` Mb
 - Memory free (cache)       = `free -m | head -n 3 | tail -n 1 | awk {'print $3'}` Mb
 - Swap in use               = `free -m | tail -n 1 | awk {'print $3'}` Mb
 - System Uptime             = `uptime`
 - Local IPs             = `ifconfig | grep -B1 "inet addr" | awk '$1 == "inet"{ print $2}'|awk -F: '{print $2}' |grep -v "127.0.0.1"
`
 - Public IP                 = `dig +short myip.opendns.com @resolver1.opendns.com`
 - Disk Space Used           = `df -h|awk '$6 ~ /\/$/ {print $1 ": percentage used: " $5 " out of " $2 " total on " $6}'
`
################################################################
"

The expect script file's contents are as below. Give this file executable permissions afterwords with chmod:

 Filename would be ssh.exp

#!/usr/bin/expect

spawn ssh root@127.0.0.1

expect "?assword"
send "test\n"
expect "root@"
send "sleep 5\n"
expect "root@"
send "./sysstat.sh|nc -q 1 127.0.0.1 4444\n"
expect "root@"
send "echo $?\n"

expect {
"0" {send "echo 'Success !!!' \n"}
"1" {send "echo 'Something went wrong !!!' \n"}
}
send "exit\n"
interact

We will setup a netcat listener on our machine that will receive the client system information. I used ncat, a similar utility to netcat but has the -k option that will allow us to accept multiple connections instead of one.

ncat -klvp 1234

 Now, with the ncat program listening for connections, we only need to run the expect script file. This script will initiate an ssh connection with the remote client system, logs you in with the proper password, sleeps for 5 seconds , execute the sysstat.sh shell script we created, which will gather information about the system (like CPU load, RAM usage, Hard disk space, etc) and output the results to netcat. Netcat will then send this information to our ncat listener. The expect script then exits the ssh session and finishes.

Here is a sample of the output you can expect from our ncat listener|:

System Summary (collected on Tue Jul 24 18:43:53 EDT 2012)

- CPU Cores = 2
- CPU Usage (average) = 17%
- Memory free (real) = 477 Mb
- Memory free (cache) = 221 Mb
- Swap in use = 0 Mb
- System Uptime = 18:43:53 up 43 min, 4 users, load average: 0.07, 0.09, 0.12
- Local IPs = 192.168.2.15
- Public IP = 123.45.678.90
- Disk Space Used = /dev/sda5: percentage used: 41% out of 39G total on $6
################################################################

Resources / Good reading:
question-defense.com
hak5.org: expect tutorial
thegeekstuff.com