Eric had made the script much more “pythonic” and really made the code more usable and expendable which he explains in his blog post, Site monitoring with Python and cron. He had made the script accept command line arguments and even added a way to send email through Python if you didn’t want to setup your own mail daemon.

I thought his additions were a great example of open source coding in action.

What does this have to do with Nix?

Well on the surface it doesn’t directly relate to Linux. The project itself is more useful for web designers and people that host websites; however, I thought this was a perfect example of open source coding and wanted to share it with you. Open source code and community programming is what Linux was made from. This project doesn’t contribute to the Linux kernel or anything super important but it is a very simple script that is now open to the public for review and improvement.

Ever wanted to contribute to a project but didn’t know where to start?

If you ever wanted to contribute and feel part of an open source community now is your chance. I feel like this is a very small project and it could be improved by ANYONE with the smallest amount of Python experience. We are not asking you to know how a kernel works or for you to start writing device drivers, just a simple Python script. This is a great opportunity for you to learn the nature of open source software and the community that powers Linux and some of the best programs around.

I’m even going to give you the steps you need to get going!

Download Git

Download Git. (sudo apt-get install git)

Clone the Project

Make Changes

Now make some changes.

Something I personally would like to see in this code is the ability to generate a graph of response times. Other things could include:

• Threshold for alert on slow response time
• Support for a config file

I am not a Programmer but I still want to contribute!

If you are not a programmer but still want to contribute to the open source community and learn a little about how it all works please consider going to the project website and submit a feature request (click create issue). This will give us an idea about what you would like to see in the script and help shape future versions.

See you in the open source community!

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Requirements

• Dropbox
• scrot – Screenshot utility
• gqview – To optionally preview the screenshot
• xclip – To automatically copy the url into the clipboard

Installing

You know the drill, grab your package manager and install a few things.

Create a file named, ‘screenshot.sh‘ and add the following:

#! /bin/sh

# Run this and it will take a screenshot of your desktop and optionally show it to you for confirmation
# Make sure you set the shotsdir to your dropbox public dir

shotsdir=$HOME/Dropbox/Public/shots
dropboxid="INSERTYOURIDHERE"
dropboxURL="http://dl.getdropbox.com/u/$dropboxid"
delay=5 # set to 0 for no delay

file=$shotsdir/shot-`date +%Y-%m-%d-%H-%M-%S`.png
mkdir -p $shotsdir
scrot -d $delay $* $file
if xmessage -buttons "Yes:0,Nah:1" -default "upload" "Want to preview your image?"
then
    gqview $file
fi
    echo -n "$dropboxURL/shots/"`basename $file` | xclip -i

Note: This script is based on a similar one by micah on reddit.

If your Dropbox folder is not in the default path you will need to change ‘shotsdir‘. Also, change the dropboxid variable to match your Dropbox id. You can find your id buy right clicking on a file in the public folder and selecting Copy Public Link.

You can also change the ‘delay‘ variable if you want to have a delay before the screenshot is taken. This will allow you to move windows around before the shot is taken.

The real beauty lies in the fact that the script will automatically put the public url in your clipboard. To paste it to a friend simply middle click!

Make an alias

Now it would be nice not to have to change directories and type in ‘sh screenshot.sh‘ all the time.

We can set up a bash alias by editing, ‘~/.bashrc‘ and add the following line:

Now you can drop screenshots simply by typing ‘ds‘ and hitting enter.

Of course you can pick any alias that fits your fancy.

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Create a folder on a large hard drive or raid your main computer/server

For example:

On the repository machine install Unison

On the local machine connect via SSH and test that the install went ok

You should see something like, “unison version 2.27.57“.

Create a file in your repository directory:

Install Unison on the Local Machine

For a Debian based system do:

Make a folder in your home directory or wherever you want:

Then run Unison:

Note the double slash after the hostname. This is used to indicate an absolute path

You will be greeted with a message saying that this is the first time it has detected changes go ahead and hit the space bar.

Press y to confirm the “conflict” and transfer the files. This should only happen the first time you setup a new directory.

Setup Unison

Create a inhouseDropbox.prf file and stick it in ‘/home/youruser/.unison‘.

If should look something like:

root = /home/youruser/inhouseDropbox
root = ssh://youruser@yourhost//media/drobo/inhouseDropbox

force = newer
times = true
batch = true

Now we have automated preferences and just need to get rid of the password prompt for SSH. The most common method of this is making a key file.

Making a key

On the local machine do ssh-keygen.
Then scp the .pub file and append it to ~/.ssh/authorized_keys file on the remote computer.
If you need additional help on how to make SSH keys see, Setting Up SSH Keys

Automating it

Running Unison by hand doesn’t do us much good. Let’s make Cron run it every two minutes or so.

Then add the following line:

Then save the file.

To test it go ahead and drop another file in the folder and wait a few minutes. The changes should propagate to the central repository.

Troubleshooting

Use

To see if cron is running the job.

You can also append, >> /home/youruser/log.txt 2>&1 instead of > /dev/null to output all errors and regular messages to a log file in your home directory.

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Rysnc helps you transfer data from one location to another in an efficient manner. It is one of those tools that you learn to use and wonder how you lived without it. Rsync is the de facto standard in backup solutions because of its flexibility and power.

Rsync checks each file and transfers only what has changed. What does this mean exactly? Rsync will actually look and see what in the file has changed and upload only the part of the file that has changed. Unlike ftp and other transfer solutions rsync doesn’t simply re-upload the entire file.

The difference in the files are then compressed (an optionally encrypted through ssh) then sent so the transfer uses the minimal amount of bandwidth. Rsync is often used by Amazon S3 users as they must pay for bandwidth. When you are paying bandwidth bit by bit you can’t afford anything but rsync.

Rsync is Efficient but What Else Can it Do?

As you can probably tell by the name rsync is really good at syncing files across a network. If a file has changed it can detect the change and transfer only that change. This makes rsync a perfect candidate for doing incremental backups or mirroring a website.

For example to mirror one folder to another you could do:

You can also use the same technique to sync from one computer to another:

By default this will only upload new files and changes but not delete or remove files that no longer exist. To do this you can add the –delete flag. This is rsync’s way of protecting yourself from mirroring a blank directory.

Want to Sync Specific Files?

In this example we only sync .iso files.

Things to Keep in Mind

• Rsync is powerful but unforgiving
• Rsync follows the unix methodology, do one thing and do it well. Thus it doesn’t provide encryption only efficient file transferring. Run rsync through SSH if you need encryption.
• Rsync will not delete files that have been removed unless you supply the –delete flag.
• Windows doesn’t keep file modification times to better than two seconds. Use the –modify-window=2 option to get around this when syncing to Windows file shares.

Most backup senarios can be done with rsync and cron. For an example on how to create a daily weekly backup scheme check out, Use Rsync for Daily, Weekly and Full Monthly Backups.

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1. Resizing images

Unless you are doing some sort of cropping there is no reason to load up Photoshop or the Gimp. A simple command will usually suffice for almost all your image resizing needs.

If you finding yourself doing lots of image resizing during the day, this command could potentially save you a LOT of time. You can even do mass image resizing.

2. Adding a Drop Shadow to an Image

I found myself spending a ton of time adding drop shadows to images. Using a simple command I was able to create drop shadows in seconds.

Note: You must have Imagemagick installed for this command to work. Debian/Ubuntu users can use apt-get install imagemagick.

Obviously, I don’t expect you to memorize this command. To shorten it use an alias.

3. Splice Together an MP3

If you want simple MP3 splicing this command has your back:

4. Clone a Hard Drive

DD is one the most simplistic and powerful image applications out there.

5. Burn an ISO to a CD

Why open up K3B or some other program just to burn an ISO? Map this command to an alias and get burning.

Note: You need to get the info for the ‘dev=’ part by running ‘cdrecord -scanbus’

6. Video Conversions

Let’s say you want to convert an AVI to an Mpeg file:

Or convert an Mpeg to AVI:

There are all sorts of things you can do with ffmpeg.

7. Replace Words in a Text File

No need to open up a GUI text editor when you have sed.

This command from Eric’s Wendelin’s blog will replace all instances of a color in CSS with another one.

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Here are a few example of all the ways we can shutdown and reboot on a nix machine.

Power off the Machine Now

Shutdown 10 Minutes From Now

Reboot at 11pm

Cancel That

If you decide you don’t need to shutdown after all you can issue a cancel command like this:

Give a Shutdown Warning Without Actually Shutting Down

Waking your Computer up

David, from crowdway blog, posted a command that tells your computer to wake up 5 minutes from now. To try enter the command and shut your computer down.

Reboot Daily with Cron

Open up cron as root with, ‘sudo crontab -e‘ and add the following line to reboot each night at 11:55pm.

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The Code

use Net::SMTP::TLS;
my $mailer = new Net::SMTP::TLS(
	'smtp.gmail.com',
	Hello   =>      'smtp.gmail.com',
	Port    =>      587,
	User    =>      'username',
	Password=>      'password');
$mailer->mail('from@domain.com');
$mailer->to('to@domain.com');
$mailer->data;
$mailer->datasend("Sent from perl!");
$mailer->dataend;
$mailer->quit;

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We can change this default behavior by changing the MAILTO variable.

Note: This will not work if you have not setup an email server.

Setting the MAILTO variable

Cron relies on a simple text file to schedule commands. To edit this file just issue the crontab command:

To change the MAILTO variable just add ‘MAILTO=username@domain.com‘ into the crontab file.

It should look something like this:

Specify Email for Each Script

If we don’t want all output to go to the same email address we can specify the output of a particular script to go to a different email address:

Email Alerts for All but One

If you have a specific script in your crontab that you don’t want output or errors emailed to you, simply add, ‘>/dev/null 2>&1‘ to the end of the command.

To find out what else you can do with cron check out, Learning Cron by Example.

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We can have our Nix boxes report:

• Security concerns
• Hardware failure
• When mission critical tasks are completed successfully
• When backups fail
• When RAID fails
• When temperature is dangerously high
• When services are unavailable

Send Email Alert on Root Login

Certain machines require only periodic root access. This is often the case on shared servers. You can setup an email alert that will immediately notify you that someone has accessed the root account.

Login as root and edit the file, ‘~/.bash_profile’. Near the bottom add this:

Now to test it, log out of root and then log back on as root. You should now get an alert that someone has logged in as root. This script shows the time and user. You can adjust the information accordingly depending on how detailed you want it.

Example:

ALERT - Root Shell Access on: Tue Jun 30 20:06:40 MDT 2009,
nixtutor     pts/0        2009-06-30 19:47 (NixTutor)

This should work as long as your root account uses bash and you have ssmtp setup correctly.

Send Email Alert on Hardware Failure

Linux has some great hardware monitoring tools to give us an overall health status of our system. Lm-sensors can report things like, processor temperature, fan speed, and voltages of the motherboard and other components. Smartmontools can give us information for S.M.A.R.T compatible hard drives that could warn us before hard drive failure and data disaster occurs.

Using these tools and a little bit of knowledge of Bash scripting or other scripting languages like, python, perl, or ruby we can easily create automated system health checks that can report back in the event of failure via email or TXT message.

Send Email Alert to Cell Phone

There may be a time where an error on a server is so critical that it needs to be sent directly to your phone. A lot of cell phone carriers have an SMS email gateway that will forward emails to the cell phone as a text message. This allows us to use sSMTP (or any email server) to send out text messages directly to our phones.

For example if I wanted to send a text message to a phone on the Verizon network I would use, 1234567891@vtext.com.

For a complete listing of SMS gateways you can see this article, How to: Send a TXT Message Through Email.

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The Code

import smtplib

fromaddr = 'fromuser@gmail.com'
toaddrs  = 'touser@gmail.com'
msg = 'There was a terrible error that occured and I wanted you to know!'

# Credentials (if needed)
username = 'username'
password = 'password'

# The actual mail send
server = smtplib.SMTP('smtp.gmail.com:587')
server.starttls()
server.login(username,password)
server.sendmail(fromaddr, toaddrs, msg)
server.quit()

What Now?

You will want to use this with an already existing script or a script where you want to add email alerts. For example:

# A big task
...
if task.completedOk():
     # Insert email code here, explaining that
     # the task is done and some details about it

Or perhaps you wanted Python to send you an email if the server room gets too hot:

# Get temp
...
if temperature > 70:
     # Insert email code here

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