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Filesystem free space monitoring

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Filesystem free space monitoring is probably one of the most widely used types of monitors in existence. It is deployed in some form in most organizations that use monitoring. We will discuss this topic using Perl as an implementation language.

First of all despite looking pretty trivial this is actually a pretty complex task. This is because there are many factors that you need to take into account -- thresholds for each filesystem can be different, Action required if "fatal" threshold is breached are individual for each server (or application).

There are several important issues in writing such a script:


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[Nov 14, 2010] Perl script to monitor disk space and send an email by Vivek Gite

This approach is wrong. Filesys::DiskSpace is not maintained, primitive and better should not be used

How to write a perl script that can monitor my disk space under UNIX or Linux and send me an email alert?

There is a nice perl system routine called Perl df or Filesys::DiskSpace. This routine displays information on a file system such as its type, the amount of disk space occupied, the total disk space and the number of inodes etc. This is not a standard module and you need to install it Filesys::DiskSpace

First you need to install this perl module using apt-get or from cpan (Comprehensive Perl Archive Network).

$ sudo apt-get install libfilesys-diskspace-perl

Perl script code to monitor disk space

Now write a perl script called
$ vi
Append following code:

use strict;
use warnings;
use Filesys::DiskSpace;

# file system /home or /dev/sda5
my $dir = "/home";

# get data for /home fs
my ($fs_type, $fs_desc, $used, $avail, $fused, $favail) = df $dir;

# calculate free space in %
my $df_free = (($avail) / ($avail+$used)) * 100.0;

# display message
my $out = sprintf("Disk space on $dir == %0.2f\n",$df_free);
print $out;

Save and close the file. Run this script as follows:
$ chmod +x
$ ./

Disk space on /home == 75.35

So /home has 75.35% free disk space. Next logical step is to compare this number to limit so that you can send an email if only 10% free disk space is left on /home file system. Here is the code with

use strict;
use warnings;
use Filesys::DiskSpace;

my $dir = "/home";

# warning level 10%
my $warning_level=10;

my ($fs_type, $fs_desc, $used, $avail, $fused, $favail) = df $dir;
my $df_free = (($avail) / ($avail+$used)) * 100.0;

# compare free disk space with warning level
if ($df_free %0.2f%% (WARNING Low Disk Space)\n",$df_free);
print $out;
my $out = sprintf("Disk space on $dir => %0.2f%% (OK)\n",$df_free);
print $out;

Run script as follows:
$ ./

Send an Email – Disk space on /home => 3.99% (WARNING Low Disk Space)

Here is final code that send an email alert ( download):

# Available under BSD License. See url for more info:
use strict;
use warnings;
use Filesys::DiskSpace;

# file system to monitor
my $dir = "/home";

# warning level
my $warning_level=10;

# email setup
my $to='[email protected]';
my $from='[email protected]';
my $subject='Low Disk Space';

# get df
my ($fs_type, $fs_desc, $used, $avail, $fused, $favail) = df $dir;

# calculate
my $df_free = (($avail) / ($avail+$used)) * 100.0;

# compare
if ($df_free Read man page of this module by typing following command:
$ man filesys::diskspace • View topic - Perl script to monitor free disk space and send email alert

  1. #!/usr/bin/perl -w
  2. # Script to check free diskspace and email notifications. Change the email and alert levels and you should be good to go.
  3. # created by lb
  4. use strict;
  5. # Alert levels Warning and Critical - Below what percent level of free disk space do you want an alert?
  6. my $alert1 = 30; #Warning level free space below 30%
  7. my $alert2 = 10; #Critical level free space below 10%
  8. # Put the email address to notify here
  9. my $email = '[email protected]';
  10. my ($size,$used,$avail,$use,$mounted);
  11. my $message;
  12. my @list;
  13. my $sysname = `/bin/uname -n`;
  14. chomp $sysname;
  15. my @df = `/bin/df`;
  16. my $df;
  17. foreach $df (@df) {
  18. if ($df =~ /\/\n/) {
  19. @list = split(/\s+/, $df);
  20. }
  21. else {next;}
  22. }
  23. # Check the usage
  24. my $diskfree = (($list[3]) / ($list[2]+$list[3])) * 100.00;
  25. # Round the number off to 2 decimals
  26. $diskfree = sprintf("%.2f", $diskfree);
  27. # See if free disk space is below any of our levels
  28. if ( ($diskfree < $alert1) && ($diskfree > $alert2) ) {
  29. $message = "Warning Diskspace threshold space below $alert1% at $diskfree%\n";
  30. &mailer;
  31. }
  32. elsif ( ($diskfree < $alert1) && ($diskfree < $alert2) ) {
  33. $message = "Critical Diskspace threshold space below $alert2% at $diskfree%\n";
  34. &mailer;
  35. }
  36. else {
  37. $message = "Free diskspace is good at $diskfree%\n";
  38. }
  39. #Output to terminal (comment out if you wish)
  40. print $message;
  41. print "~" x 75, "\n@df","~" x 75,"\n","From system: $sysname\n";
  42. #Subroutine for Mail, notifies on warning and critical levels.
  43. sub mailer {
  44. open(MAIL, "|/usr/sbin/sendmail -t") or die "Cannot open sendmail!: $!";
  45. print MAIL "To: $email\n";
  46. print MAIL "From: $sysname\n";
  47. print MAIL "Subject: $message\n\n";
  48. print MAIL "$message";
  49. print MAIL "~" x 75, "\n@df","~" x 75,"\n","From system: $sysname";
  50. close(MAIL);
  51. }

use FilesysDiskspace - Perl answers

I want to monitor disk space and send a email if it exceeds the limit.
I m using "use Filesys:: Diskspace" but there is an error in compling.

Expand|Select|Wrap|Line Numbers

  1. "Can't locate Filesys/ in @INC (@INC contains: /etc/perl /usr/local/lib/perl/5.8.4 /usr/local/share/perl/5.8.4 /usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.8 /usr/share/perl/5.8 /usr/local/lib/site_perl .) at line 4.
  2. BEGIN failed--compilation aborted at line 4."


That is not part of the core modules of perl:

So as Kevin states, you'll have to install it:

I'm not certain this'll be a module you want to use though. By browing the cpan description, you'll notice that the module has not been updated since 1999. This might be a problem, but I would consider looking through the other Filesys modules to determine if there is one that might be better, as in maintained more frequently and therefore supports more file systems.


Ximinez is a disk usage analyzer and comparator. It enables you to take snapshots of disk usage for a given folder, to browse through the snapshots, and to view differences between snapshots. It is aimed towards solving problems like: "Why is my disk suddenly so full when it was OK just recently?" Besides the GUI, the package also includes an optional command line tool, which can be used, for example, in conjunction with a scheduler to take snapshots on a regular basis.
Tags Systems Administration Filesystems
Licenses BSD Revised
Operating Systems OS Independent
Implementation Python
Translations Slovenian English

System monitoring tools

On Tue, 18 Aug 1998, chuck wrote:

First off, I really enjoyed your email.

> Frankly, a good automatic monitoring tool should be able to do
> what you do by hand but better.  If an important machine goes
> down or is heading for trouble, I want to know ahead of time.
> Watcher (or SNMP) can alter you when a disk reaches 95%.
> Watcher can note that a partition is filling fast or that a
> process is running away.  Yeah, you should know that machines,
> but you can automate a lot of this (see bottom for a rebuttal of
> this:)

As I mentioned before I just got done implementing a monitoring system
(using Tivoli, arg, which basically just calls shell scripts that I
wrote ;). One 'big picture' thing i formalized in my implementation
was 'reactions'.  I mean, it's great that now I *know* the drive is
filling up, but what now?  For all of our 'events' I automated reactions
to deal with them.  In the example of disk space, a script gets run which
does a find on the filesystem for all files mod in the last 24 hours and
sorts them by size and emails it to the admin on duty.

I am very pleased with the 'reactions' i have put in place, because now,
not only am i aware of things going wrong, but the first steps i would
take are already taken, and I can just analyze instead of doing grunt

> #################### ALERTING: ####################

I established three different levels that did different things.  Warning,
Severe and Critical.  Warning just an email, severe email and popup,
critical, page email and popup.  This made it very easy to 'classify'
events.  My environment is not very large (OK, it's small), but it has
been a timesaver for me.  

> but it got us bonus points from auditors and data security.

heh, that's cool.

> Can Tivoli(/SNM/Openview) do this?  Well, kinda sorta, not really.
> You have a nice GUI. that makes some people feel good.  You have
> an API (and every SA has time to learn an API to write their
> scripts in C to talk to these tools); you have support
> (generically).  You have someone else to shoulder responsibility;
> vaguely.

bingo.  in Tivoli's defense the underlying architecture (CORBA) is pretty
solid, and you are given the tools to customize easily.  But out of the
box (for Distributed Monitoring) it's useless.  It seems as though these
products are being developed by ppl that are marketing types vs. admins
who have been in the trenches.

> I want something adaptive ("the machines are usually quiet now, but
> today they aren't, please note")  Nothing replaces ME watching the
> machines and even the graphs (oh sendmail's running hotter than
> usual for a sunday).  I want that.  Must I relearn prolog?

I think that is *very* key.  In my documentation of my implementation I
state, "No software product in the world is going to be able to provide
the root of what needs to happen.  Competent system/network architecture
and operations.  Experience is the only thing I have seen which can really
provide that."

For some reason it seems as though IT managers think software can fix all
of their problems when odds are it's not the software or hardware that
needs fixing, it's the ppl.

> Perhaps a SAGe group to cover SA tools like this might be of
> interest (even just a web page as a resource).  Perhaps I volunteer
> (as long as someone else does the pretty pictures); I'll poke at it.

I would be into that.  Email me directly if you would like to brainstorm.
I have seen a lot of details on how to do this and that with monitoring,
but have yet to see a resource that covers the 'big picture' thinking (ie.
create a loghost for your network, use email address roles <-you really
don't want to have to change email addresses is mucho scripts when bob
leaves do you?, etc).

Scott Walters

"The world speaks IP"

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