Add Services In Linux Using chkconfig

As a SysAdmin, you are responsible for everything to do with the systems under your control.  These responsibilities range from system installations to all kinds of maintenance and updates.  You may find, now and again, that you want to have something start up when the machine boots, and the best way to do that is to have an /etc/init.d script to do that for you.  In these scripts, you can define start, stop, restart options, with the commands you want to happen for each option.

To begin, a really handy command that you should get to know is chkconfig.  This command will show you whether a service is set to be on or off in each runlevel.  If you simply type the command with no options, you will see output like the following:

     httpd         0:off   1:off   2:on    3:on    4:on    5:on    6:off

As you can see, the runlevel's are shown, with the corresponding on/off option shown for each.  In order to add a service, you need to first create the script to execute and put it into the /etc/init.d directory.  If you have software that you have unpacked that has its own script already written, you can simply create a link to that script in the /etc/init.d directory.  Either way, once you have done that you can add it as an active service by issuing:

     chkconfig --add

The is the script or link name that you just put/created in /etc/init.d.  After adding it, check that it was successfully added by doing:

     chkconfig | grep

You should see the above output if the service was successfully added.  If you need to change a service to be on or off in a specific runlevel, then the format of the command is:

     chkconfig --level 345 httpd off

The numbers after the '--level' are the runlevels to modify.  As you can see, you can list whichever levels you want, but no spaces, commas, or anything else. After that is the service to modify, followed by whether it is off or on in the listed runlevels.

To remove a service, simply use:

     chkconfig --del

Again, check that it was removed per the above command.

The chkconfig command does have other options available to it, but this should give you a basic overview of how to use it.  If you wish to read further, please feel free to read the man page.

It is important to note that chkconfig does not exist on all systems and is typical on Red Hat based systems.  If you are on, say, Debian based machines (such as Ubuntu), then you will need to use 'update-rc.d'.

We will save that for another post.....

Removing Files Older Than So Many Days In Linux

On our own home systems, we tend not to run into the issue of files from this product or that product, building up and eating your disk space.  But, when you are dealing with servers and the software that people run on them, preserving space by deleting unnecessary logs and other files, is a necessary skill.

Just as an example, we use Puppet where I work to manage system configurations.  While the puppet logs tend to take up a bit of space on our puppet server after a while, its the puppet reports that end up eating the most space.  

The puppet reports are located in /var/lib/puppet/reports.  Under that directory is/are (potentially) a whole slew of directories, one for each machine that puppetizes off of that master.  In each of those directories are *.yaml files.  A yaml file is created each time puppet runs on a machine and connects to the puppet master.  

So what is the first step in purging the files?  Well, lets start by seeing how many files we are actually talking about.  To do this, you can use the find command:

   find /var/lib/puppet/reports *.yaml | wc -l

What that command does is search the reports directory for all yaml files.  It then reports the total cound of all files found.  Next, lets see how many files we are looking at getting rid of.  Let's say that we are going to keep the last 14 days of files.  For that we would simply modify the above command to be:

   find /var/lib/puppet/reports *.yaml -mtime +14 | wc -l

Again, it will report the total.  You will notice that the number is smaller than the previously reported number.  Now, if you are ready to remove those file, a simple modification will do that for you:

   find /var/lib/puppet/reports *.yaml -mtime +14 -exec rm {} \;

You have to just love the power of the command line in unix.  With just a few keystrokes, you can purge the unneeded files with a single command and a few options.  

Free Programming Books and Links

There is no question, Free is just one of those words in the English language that when see, people take notice.

I stumbled across a link to some Free programming books and links that I feel just needs sharing.  Now before you get too excited, the links on that page either take you to either an online version of a book, or a link to a page with a tutorial or article.

To be honest, I have found a bunch of good information in here since finding it and hope that you do as well.

NEW OpenSSL Vulnerability

For those who haven't heard, there is a new OpenSSL vulnerability that was found, dubbed Heartbleed.
If you haven't done any patching yet, you'll want to if you have an effected version of OpenSSL installed on your system(s).

You can test your sites with this software, released today.

To check your systems to see which version of openssl is installed, simply run 'openssl version' and check what it reports.  Versions 1.0.0 and 0.9.8 are NOT effected, but if you are at version 1.0.1 or above, you will need to patch to version 1.0.1g (the newest, released version to fix the issue).

If you are using Amazon AWS, here is how you can update your instances.  Also, Amazon has launched a new AMI that contains the fix as well.

Just a note about the Amazon instructions, you'll need to use the following command to unpack the tarball:

     tar -xvf

The article incorrectly states a command that simply hangs and the above will extract correcty.

NOTE:  Since the writing of this post, the article has been updated to include the 'f' option.

If you are using openvpn, then you may find the application was pre-compiled with openssl 1.0.1e or another effected version, making it a static build.  I heard that OpenVPN is supposed to be releasing an update that uses 1.0.1g.

UPDATE:  Here is a link to a reddit post that provides further information on the bug.

Getting Back To Some Linux Basics

Yogi Berra is famous for many '-isms' which make people laugh.  One of those '-isms' that I like is:

       "Life is a learning experience, only if you learn"

One of the things I love about my job is that I learn something new every day.  While I have learned a lot over the years (thus far), I also am humble enough to know that there are so many things that I don't know.  

In the spirit of learning, l wanted to share with everyone a link to some Linux basic commands.  While Linux has a friendly GUI front end to it which makes it easy for someone new to the operating system to get around and get used to it, the true power of the operating system lies in the command line.  Some would say its a dying art, but I refuse to believe that.  There is so much you can do on the command line, faster than you can through a gui, that it will never truly go out of style.  

Here is a link to a nice set of Linux commands that not only give a quick overview, but they also give examples of the commands being used as well.  What was even nicer about the folks over on that site, they even created a pdf version of the page.  Please keep in mind though that the pdf version does not contain all of the examples that are linked to in the main page.  

That page (and accompanying pdf file) are only a small subset of the commands available in Linux.  If you are looking for a more complete reference, here is one that goes over the commands that are part of the Bash shell (one of the more popular shell environments in Linux).

And, last but certainly not least, for those of you who are anal enough (like me) to want a complete reference, here is a link to an online version of the Linux Complete Command Reference (pdf version).

Even if you don't make Linux part of your career, its beneficial for you to check it out.  Not only is it far more secure than Windows and none of the virus' effecting Windows based systems can effect Linux, but its also FREEEE!!!!!   I know, as my Dad asked me before I switched him over, "Where will I get support?"  My answer to him was "Me!".  To you, my answer is "Google!".  Its the best support reference I can give other than knowing someone who knows it.  

Enjoy!