Monitor VPS system resources using shell scripts

VPS was used a few months ago, with a traffic limit of GB per month, which is enough for convenient traffic. However, due to some malicious access, resources such as CPU and Memory consume a lot, as a result, the response time of a blog website on VPS is too slow or sometimes the webpage cannot be opened. Therefore, I made a simple script for monitoring and sending an alarm by email. Because it is not very professional O & M, I do not want to use very professional monitoring tools, such as Nagios, Puppet, Cacti, and Zabbix, So I manually set a Shell script to monitor me.

VPS was used a few months ago, with a traffic limit of GB per month, which is enough for convenient traffic. However, due to some malicious access, resources such as CPU and Memory consume a lot, as a result, the response time of a blog website on VPS is too slow or sometimes the webpage cannot be opened. Therefore, I made a simple script for monitoring and sending an alarm by email.
Because it is not very professional O & M, you do not want to use very professional monitoring tools, such as Nagios, Puppet, Cacti, and Zabbix, therefore, I manually set a Shell script to monitor CPU, Load, Memory, network transmission, and whether a blog website can be opened. Share the monitoring script as follows:
Https://github.com/smilejay/shell/blob/master/sh2013/vps_monitor.sh

#!/bin/bash#set -x# the script to monitor my VPS# It will alert when memory, load, CPU%, networking, httpd/mysqld or home-page# is in an abnormal state.# author: Jay# date: 2013-10-16     EMAIL="smile665@gmail.com"WARN_MSG=""     # alert when free memory is less than 50 MBfunction mem_free(){        threshold=50 # 50 MB free memory        free_mem=$(free -m | grep "buffers/cache" | awk '{print $4}')        if [ $free_mem -lt $threshold ]; then                WARN_MSG=$WARN_MSG"Free memeory is less than $threshold MB.\n"                return 1        fi        return 0}     # alert when load (5min) is larger than 4function load_avg(){        threshold=4 # load is 4        load_5min=$(cat /proc/loadavg | awk '{print $2}')        if [ $(echo "$load_5min > $threshold" | bc) -eq 1 ]; then        WARN_MSG=$WARN_MSG"5min average load is larger than $threshold.\n"                return 1        fi        return 0}     # alert when CPU idle% is less than 20%function cpu_idle(){        threshold=20 # CPU idle% 20%        cpu_idle=$(sar 1 5 | grep -i 'Average' | awk '{print $NF}')        if [ $(echo "$cpu_idle < $threshold" | bc) -eq 1 ]; then                # in printf cmd, %% represents a single %                WARN_MSG=$WARN_MSG"CPU idle%% is less than $threshold%%.\n"                return 1        fi        return 0}     # alert when networking tx speed is larger than 80 kB/sfunction network_tx(){        threshold=80 # TX speed 80 kB/s        interface=eth0        tx_speed=$(sar -n DEV 10 5 | grep "Average" | grep "$interface" | awk '{print $6}')        if [ $(echo "$tx_speed > $threshold" | bc) -eq 1 ]; then                WARN_MSG=$WARN_MSG"networking TX speed is larger than $threshold kB/s.\n"                return 1        fi        return 0}     # alert when httpd or mysqld process doesn't existfunction httpd_mysqld(){        ps -ef | grep 'httpd' | grep -v 'grep'        if [ $? -ne 0 ]; then                WARN_MSG=$WARN_MSG"httpd process doesn't exist.\n"                return 1        else                ps -ef | grep 'mysqld' | grep -v 'grep'                if [ $? -ne 0 ]; then                        WARN_MSG=$WARN_MSG"mysqld process doesn't exist.\n"                        return 1                fi        fi        return 0}     # alert when 'Stay hungry' doesn't exist in the home page http://smilejay.com/function home_page(){        url=http://smilejay.com/        keywords="Stay hungry"        curl -sL $url | grep -i "$keywords"        if [ $? -ne 0 ]; then                WARN_MSG=$WARN_MSG"keywords '$keywords' doesn't exist on link $url.\n"                return 1        fi        return 0}     # use an array to store the return value of each monitoring functionmem_freechk[1]=$?load_avgchk[2]=$?cpu_idlechk[3]=$?network_txchk[4]=$?httpd_mysqldchk[5]=$?home_pagechk[6]=$?     # send warning email to the web master if any of the check fails.for i in $(seq 1 6)do        if [ ${chk[i]} -ne 0 ]; then                printf "$WARN_MSG" | mailx -s "Warning from smilejay.com" $EMAIL                exit 1        fidone