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Writing Monitoring Scripts

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The structure of the event Programming Monitors in Perl Perl Monitoring Scripts Using Perl to simulate Telnet from a Program  


Filesystem free space monitoring   Humor Etc

For any good monitoring solution the quality of the probes is the key. Otherwise this is "garbage in -- garbage out" situation...

Many Unix utilities can be reused as probes using some scripting language wrapper. For example,  most UNIX systems have sar utility output of which can be piped into Perl script and/or converted into html.  The latter  can be send as a status report to a monitoring Web-server. Sar usually runs periodically from the cron (for example each 15 minutes) but you can implement any type of scheduling you wish.  Similarly the most basic heartbeat capabilities can be achieved using ping or similar  module in Perl, Python or other scripting language.  It is important to design and use a unified architecture for the most probes (some specialized probes can, of course, represent an exception). As Damir Delija  aptly noted in his Sys Admin  article  Unix Monitoring Scripts:

A monitoring tool or script is part of system management and to be really efficient must be part of an enterprise-wide effort, not a standalone tool. Its purpose is to detect problems and send alerts or, rarely, to try to correct the problem. Basically, a monitoring/alerting tool consists of four different parts:

  1. Configuration -- Defines the environment and does initializations, sets the defaults, etc.
  2. Sensor -- Collects data from the system or fetches pre-stored data.
  3. Conditions -- Decides whether events are fired.
  4. Actions -- Takes action if events are fired.

If these elements are simply bundled into a script without thinking, the script will be ineffective and un-adaptable. Good tools also include an abstraction layer added to simplify things later, when modifications are done.

Generally in any monitoring task Perl is your friend and there is tremendous amount of free Perl probes available on internet either as standalone modules/utilities or as a part of monitoring packages. Usually they are well-written, quite simple and thus can be adapted to your task without too much effort. For example, if you want to  monitor web logs such packages as W3Perl can be quite handy.

In any monitoring task Perl is your friend and there is tremendous amount of free Perl probes available on internet either as standalone modules/utilities or as a part of monitoring packages. Usually they are well-written, quite simple and thus can be adapted to your task without too much effort.

Many probes can be created as a simple Perl wrappers around a command whose results are important for judging health of the server, subsystem (CPU, disk space, etc) or particular application. If you put some efforts to develop common structure and that enforce it  (adopt unified probe architecture) then you can achieve significant savings in writing code for them and will spend less time and efforts on maintenance. You may even adopt some of the existing packages probes architecture, for example mon or Nagios and not to try to reinvent the bicycle.

Careful selection and adoption (with possible extension on one of existing probes architecture is important for successful custom monitoring infrastructure development. It's important nor to reinvent the bicycle

As soon as you have a set of useful probes, you need the infrastructure to run them. In many  cases you do not need anything fancy and it can be really, really simple. The most  basic structure of monitoring package is an infinite loop that runs probes each polling interval. Each probe can write to named pipe that is attached to converter of key value pairs (or HTML  if you want to be fancy, but please keep it simple). Script on the other end is essentially an agent -- the code designed to pass the message to the server.  For remote probes SMTP mail can be used as the simplest delivery mechanism or probes can directly communicate with the WEB server via Web forms.

Here is the subset of probes used on old Tivoli Distributed monitoring

Disk Resource Monitoring Sources

 Inodes free  inodes
 Inodes used  inodesused
 Percent inodes used  inodesusedpct
 Percent space used  diskusedpct
 Space free  diskavail
 Space used  diskused
 Tivoli DB free space  tivdbspace

Security Monitoring Sources
 Check file permissions  fileperm
 Compare files  filediff
 Daemon status  daemon
 File checksum  filechk
 File size  filesize
 Occurrences in file  countstr
 Process instances  daemonct
 User logins by user  ulogins
 Users logged in  ulogintot

Network Monitoring Sources

 Client RPC timeouts  rpctmout
 Host status  host
 Network collisions  netcoll
 Network collisions/packet  netcollpct
 NFS bad calls  badnfs
 Input packet errors  netinerr
 Input packets  netin
 Output packet errors  netouterr
 Output packets  netout
 Remote oserv status  oserv
 RPC bad calls  badrpc

System Resources Monitoring Sources

 Available swap space  swapavail
 Host status  host
 Lingering terminated processes  zombies
 Load average  loadavg
 Mail queue length  mailqlen
 Page-outs  pageouts

Printer Monitoring

Daemon status  daemon
 Jobs in print queue  printjobs
 Status of print queue  printstat
 Total size queued  printjobsize

User-Defined Monitoring Sources

 Asynchronous numeric  nasync
 Asynchronous string  sasync
 Numeric script  ncustom
 String script  scustom

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Source: Disk Space Monitor and E-mail Alert Script
Author: unixsysny Created Date: 8/31/2004
Author Website: none Rating: 13 of 16
Code Demo URL: none Views: 12,971
Compatibility: Korn Shell
Summary: This DISK Capacity Monitoring script could be tweaked to run as a bash script also - just happen to prefer ksh.
#! /bin/ksh

########### Function SENDMAIL will send mail to sys admins regarding disk capacity ##############

SENDMAIL () { mail -s 'Disk Space Alert' $INTERESTED<<EOF
             $PERC % ALERT
             Filesystem $FILESYSTEM has reached $PERC% of its capacity.

########## VARIABLES ###########

[email protected],[email protected],[email protected]

######### Run df -kl and extract filesystem and disk usage amount to temporary holding file ########

df -kl | grep -iv filesystem | awk '{ print $6"\t "$5}'|cut -d"%" -f1  >holding

######### reasign standard input to temporary holding file#######

exec < holding

######### Read FILESYSTEM and PERCentage, for each line execute the case test  ########


######## Test each FILESYSTEM PERCentage against it's threshold amount. If PERCentage is 
######## greater than threshold amount execute the SENDMAIL function.

case "$FILESYSTEM" in
     /) if [[ $PERC -gt 80 ]]; then
     /stand) if [[ $PERC -gt 47 ]]; then
     /proc) if [[ $PERC -gt 1 ]]; then
     /dev/fd) if [[ $PERC -gt 80 ]]; then
     /dev/_tcp) if [[ $PERC -gt 80 ]]; then
     /home) if [[ $PERC -gt 42 ]]; then
     /home2) if [[ $PERC -gt 10 ]]; then
     /system/processor) if [[ $PERC -gt 1 ]]; then
     /tmp) if [[ $PERC -gt 30 ]]; then
     /var/tmp) if [[ $PERC -gt 45 ]]; then
     /osm3) if [[ $PERC -gt 80 ]]; then
     /osm) if [[ $PERC -gt 80 ]]; then
     /osm1) if [[ $PERC -gt 84 ]]; then
     /osm2) if [[ $PERC -gt 80 ]]; then
    *)mail -s 'Invalid FILESYSTEM! found' $INTERESTED<<EOF
             Filesystem $FILESYSTEM has been discovered by the Diskmonitor Process. 


Performance Monitoring Tools for Linux Linux Journal

By David Gavin on Tue, 1998-12-01 02:00. Security

Mr. Gavin provides tools for systems data collection and display and discusses what information is needed and why.

For the last few years, I have been supporting users on various flavors of UNIX systems and have found the System Accounting Reports data invaluable for performance analysis. When I began using Linux for my personal workstation, the lack of a similar performance data collection and reporting tool set was a real problem. It's hard to get management to upgrade your system when you have no data to back up your claims of ``I need more POWER!''. Thus, I started looking for a package to get the information I needed, and found out there wasn't any. I fell back on the last resort--I wrote my own, using as many existing tools as possible. I came up with scripts that collect data and display it graphically in an X11 window or hard copy.

What Do We Want to Know?

To get a good idea of how a system is performing, watch key system resources over a period of time to see how their usage and availability changes depending upon what's running on the system. The following categories of system resources are ones I wished to track.

CPU Utilization: The central processing unit, as viewed from Linux, is always in one of the following states:

By noting the percentage of time spent in each state, we can discover overloading of one state or another. Too much idle means nothing is being done; too much system time indicates a need for faster I/O or additional devices to spread the load. Each system will have its own profile when running its workload, and by watching these numbers over time, we can determine what's normal for that system. Once a baseline is established, we can easily detect changes in the profile.

Interrupts: Most I/O devices use interrupts to signal the CPU when there is work for it to do. For example, SCSI controllers will raise an interrupt to signal that a requested disk block has been read and is available in memory. A serial port with a mouse on it will generate an interrupt each time a button is pressed/released or when the mouse is moved. Watching the count of each interrupt can give you a rough idea of how much load the associated device is handling.

Context Switching: Time slicing is the term often used to describe how computers can appear to be doing multiple jobs at once. Each task is given control of the system for a certain ``slice'' of time, and when that time is up, the system saves the state of the running process and gives control of the system to another process, making sure that the necessary resources are available. This administrative process is called context switching. In some operating systems, the cost of this switching can be fairly expensive, sometimes using more resources than the processes it is switching. Linux is very good in this respect, but by watching the amount of this activity, you will learn to recognize when a system has a lot of tasks actively consuming resources.

Memory: When many processes are running and using up available memory, the system will slow down as processes get paged or swapped out to make room for other processes to run. When the time slice is exhausted, that task may have to be written out to the paging device to make way for the next process. Memory-utilization graphs help point out memory problems.

Paging: As mentioned above, when available memory begins to get scarce, the virtual memory system will start writing pages of real memory out to the swap device, freeing up space for active processes. Disk drives are fast, but when paging gets beyond a certain point, the system can spend all of its time shuttling pages in and out. Paging on a Linux system can also be increased by the loading of programs, as Linux ``demand pages'' each portion of an executable as needed.

Swapping: Swapping is much like paging. However, it migrates entire process images, consisting of many pages of memory, from real memory to the swap devices rather than the usual page-by-page mechanism normally used for paging.

Disk I/O: Linux keeps statistics on the first four disks; total I/O, reads, writes, block reads and block writes. These numbers can show uneven loading of multiple disks and show the balance of reads versus writes.

Network I/O: Network I/O can be used to diagnose problems and examine loading of the network interface(s). The statistics show traffic in and out, collisions, and errors encountered in both directions.

These charts can also help in the following instances:

This sort of information will often show up as a spike in the charts at times when the system should have been idle. Sudden increases in activity can also be due to jobs run by crontab.

Unix Server Monitoring Scripts

These scripts monitor web servers, disk space, dns and SMTP servers using ksh shell, wget, basic Perl modules. Its goal is to be easy, simple to use. You may use one, none, or some of the scripts, as they are all independent.

Installation of the scripts consists of:
  1. Creating a local user to run each script and schedule these through that user's crontab. You may run each script with any user capable of running wget, df -k, and top. I suggest creating a user called monitor.

  2. Extracting and placing all scripts (Main and Support) on a web server and making them executable. Also move images to an images directory under your web root.


    tar zxvf monitor_suite.tgz
    mkdir -p /usr/local/admin/bin
    mv *sh /usr/local/admin/bin/
    mv *pl /usr/local/admin/bin/
    chmod 755 /usr/local/admin/bin/*
    mv *gif /var/www/html/images
    chown monitor.monitor /usr/local/admin/bin/*

  3. Read through each main mon*.sh script and fill out local variables (For example your webroot and pager recipient).

  4. Creating a directory under the root of your web server where the scripts will write its logs and history. I used webmon for The other scripts are similar: I used smtpmon for and stats for is different in that is the only one installed locally on each server you wish to monitor.


    mkdir /var/www/html/smtpmon/
    mkdir /var/www/html/webmon/
    mkdir /var/www/html/dnsmon/

  5. Make sure the user running the scripts have permission to write to the script home.

    chown monitor /var/www/html/smtpmon/
    chown monitor /var/www/html/dnsmon/
    chown monitor /var/www/html/webmon/

  6. Move Support Files into place in the new script homes:

    cp footer.txt /var/www/html/smtpmon/
    cp footer.txt /var/www/html/webmon/
    mv smtpservers.txt /var/www/html/smtpmon/
    mv smtp_header.txt /var/www/html/smtpmon/
    mv urls.txt /var/www/html/webmon/
    mv dnsservers.txt /var/www/html/dnsmon/

  7. Installing wget if not on your Unix/Linux Distribution (for

  8. Installing NET::SMTP Perl module if not on your Unix/Linux Distribution (used in and

  9. Installing NET::telnet Perl module if not on your Unix/Linux Distribution (for and (used in

  10. Setting up in cron.

    For Example:

    #-->Web monitor
    0,5,10,15,20,25,30,35,40,45,50,55 * * * * /usr/local/admin/bin/ > /dev/null 2>&1
    #-->Smtp monitor
    0,5,10,15,20,25,30,35,40,45,50,55 * * * * /usr/local/admin/bin/ > /dev/null 2>&1
    #-->DNS monitor
    0,5,10,15,20,25,30,35,40,45,50,55 * * * * /usr/local/admin/bin/ > /dev/null 2>&1


  1. Each wget log is about a half a k. (500 bytes). Multiply this times the number of servers you are monitoring, times the frequency you are monitoring (ie. every 5 minutes equals 12 times an hour, 288 times a day) to understand how much space you need for history. As a reference we have 10 production web servers being monitored 24x7, 6 months of logs take up about 500 MB.
  2. Each smtp log is about 1.5k. This includes debugging info (recommended, not required)
  3. Each successful dns log is about 200 bytes. Each error log about 1k.
  4. Logging for is either through cron or via use of wrapper script. Or you may modify the source.
  5. We are using the insecure rsh protocol in the script to show you how to get this setup quickly, but it recommended you use ssh with properly distributed keys to gain security.
  6. Support files for each script (if needed) are listed directly below the script.
  7. If you get a "bad interpreter" message, make sure the first line points to a valid shell you have installed. (ksh and bash should both work)
  8. I suggest using IPs addresses for your defined SMTP servers to send alerts through (or use host files), in case of a DNS outage.


  1. Admin view of Monitor_web
  2. Admin view of Monitor_stats
  3. Drill down view of Monitor_DNS

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Scripts Category UNIX System_administration Project details for Unix Server Monitoring Scripts

Monitoring Unix System Processes with Psmon by Nicola Worthington

Psmon is a system monitoring script written in Perl and licensed under the Apache license that is quite useful if you run servers with critical processes on them. You can download the latest version from the psmon homepage (Version 1.39 as of this writing). Read on for tips on installing and configuring it.

Sys Admin/Unix Monitoring Scripts by Damir Delija

Linux, UNIX system Monitoring - Bash shell scripts directory



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