Desktop Systems Engineer and Analyst
Volume Number: 22 (2006)
Issue Number: 3
Column Tag: Interview
In The Trenches
Desktop Systems Engineer and Analyst
by Schoun P. Regan
Interviewing Kevin Denges: Kevin is in charge of the image creation and deployment for Conde Nast. I spoke with him in New York City, at his office.
Schoun: Kevin, tell me about the setup.
Kevin: We have a Windows Active Directory infrastructure for authentication. The Macs are bound to the Active Directory server and the Xserves are used as image servers, primary and secondary K4 servers. K4 is our Adobe InDesign workflow. Each server is setup using 2 Xserve's, one primary and a second mirror for failover. We started all this with Mac OS X 10.3.3, so we've been at it for some time.
Schoun: And for file servers?
Kevin: We are using Extreme z-ip version 4. We started to deploy them in Sept/Oct of this year to our Windows servers, and by doing so, now have single sign on using Kerberos.
Schoun: What about the Macs? How are they deployed? NetBoot?
Kevin: No. The Xserves are just image servers for the most part. We use FireWire drives to deploy our images, but we also store those images on a server. So if a tech ever needs to get a newer image, they boot off of a FireWire drive and install the latest image from our servers.
Schoun: Sounds like NetBoot may solve the booting from FireWire issue.
Kevin: We are looking into that, but for right now, FireWire drives are the most efficient for us.
Schoun: So one image to rule them all?
Kevin: Nope. We have an image that has all the software they need, and one main image. There are older images with 10.3 on them also. It depends on where the computer is placed and with whom as to what image they receive on their Mac.
Schoun: So the image build, it's stock Mac OS X?
Kevin: For the most part yes. We have leveraged the power of launchd to handle some initial binding and computer setup for us, but other than that, it's stock with Adobe's CS2 suite.
Schoun: Take us through the launchd file.
Kevin: Well basically it's very simple, it starts when the machine boots and runs a shell script that we have. Here's what it looks like:
Figure 1.
Kevin: We also have another launchd item that handles the fixing of ByHost files.
Schoun: First tell me about the AD binding launchd item:
Kevin: As you can see, it runs at boot time, waits 2 seconds, then renices to get processor authority, to run ahead of other items. It then calls the shell script ADhook.sh located in a directory I chose. Pretty simple actually.
Schoun: Is the ByHost launchd item the same?
Kevin: For the most part yes, except it calls another script of course.
Schoun: So lets look at the AD script then. We know that the Active Directory plug-in has a command line counterpart, dsconfigad. I assume you use this?
Kevin: It's now a small part of the script, but yes, it is the integral part. The script is divided into four major parts; network connectivity, AD binding, ByHost fixes, and file deletion.
Schoun: Can we walk through some of the major portions of the script?
Kevin: Sure, but keep in mind that some of this came from Mike Bombich's site, so credit goes to him for some of this.
Schoun: I'll let him know.
Kevin: So as we can see, the first part of the script creates a log file for us to write to, then we check for network connectivity.
Figure 2.
Schoun: I see Vicki in here.
Kevin: Yes. The problem we sometimes encountered was that a tech would download an image, and reboot the Mac only to find the Mac was not on the network. Or, in certain cases, the Macs would unbind and we would have to rebind them. Either way, the script now checks for not just network connectivity, but if the Mac is connected to our network. It announces its findings using the voice Vicki on the Mac. This way our techs know whether the machine is binding or not.
Schoun: Part of this script looks familiar.
Figure 3.
Kevin: [laughs] I borrowed-and gave credit to-Mike Bombich as this is based on the script called, "Who stole my Mac script". It was important to us, to make sure our techs knew what the status was, when they imaged a machine. This helps us track binding issues.
Schoun: Let's talk about the AD binding.
Kevin: Sure. Before I run the actual bind, I set all the parameters. This part of the script sets the parameters.
Figure 4.
Schoun: I see the uuidgen command in there! I should explain to our readers that uuidgen is a command that creates a unique ID, unique enough that the man page states, "The uuidgen command generates a Universally Unique Identifier (UUID), a 128-bit value guaranteed to be unique. A UUID is made unique over both space and time by combining a value unique to the computer on which it was generated--usually the Ethernet hardware address--and a value representing the number of 100-nanosecond intervals, since October 15, 1582 at 00:00:00." You gotta love Apple code writers sometimes. "Unique over space AND time" Ha.
Kevin: Well, the issue is that if a Mac binds to an AD domain, the AD domain cannot use that computer name to bind more than twice. So, if a computer's name is already in the AD domain, and our techs re-image it, the bind fails. Using a portion of the uuidgen output insures us a unique ID with which to bind the Mac.
Schoun: I also see that you did not put the password into this script for the actual bind. That you are calling the output of an AppleScript file. Why?
Kevin: Security. This way the script calls the AppleScript file and it returns the password. Just a little more secure this way.
Schoun: So with all the variables set, now the bind?
Kevin: Yes. Again we used the dsconfigad command line tool for that. We of course write to the log file, check for an older edu.mit.Kerberos file and get rid of it, if one exists, and set the search policies.
Figure 5.
Schoun: I see a sleep command in there.
Kevin: It seemed to go smoother when we did this.
Schoun: Then the ByHost issues? Why the problem?
Kevin: As you know, ByHost files are MAC address specific, so we have them set the way we want, then we put all Xs in the place of the address. We then copy these and replace the Xs with the local Mac's MAC address. We do this for the template for any user's that log in via AD, our local administrator account, and a hidden account we have.
Figure 6.
Schoun: And the last part of the script?
Kevin: Checking the bind, having Vicki notify the tech, and then deleting the launchd item, the AppleScript file with the password, and then deleting itself, killing the loginwindow process and having it come back. This way, the AD user can log in and get a newly created home folder, with all the customized tweaks we've added in the user template, such tweaks to the .GlobalPreferences file, the Dock, the menu bar, the screen saver, the background, and so on.
Figure 7.
Schoun: This is in incredibly powerful script. Again I see some of Mike's work in here, but you have done a nice job of pulling it all together.
Kevin: Thanks. Our next step is to take this and make a launchd item that watches the bind and if it fails, it deletes the /Library/Preferences/edu.mit.Kerberos file, the DirectoryServices directory inside of the same location, and pulls them from a hidden location on the local disk and rebinds the machine automatically.
Schoun: I would also suggest, you use the mail command to email an administrator account, when this occurs. In this way, your techs can be a bit more proactive than reactive. They will know when a machine unbinds.
Kevin: Yea. We want to do more with launchd and scripts.
Schoun: Kevin, this is all we have time for, but I know you have more to say about your setup. I think this script is an excellent place to start. It gives the reader a clear- cut way of implementing this type of bind. I'd like to talk to you more about how this interacts with the local NetInfo database and what other tweaks you've done to the system.
Kevin: Be happy to. We are very confident in our process, and have moved to cut down time to under 5 minutes, if possible.
Schoun: I think our readers will be excited to learn about what else you have done.
Ed Note: Kevin has much more to say about his infrastructure but this time I wanted to focus on the script itself.
Vital Stats
Years in IT industry : 6
Information: Kevin is in charge of the image creation and deployment for Conde Nast.
Computers: About 2700 Macs, 42 Xserves, 4 Xserve RAIDs, Windows Active Directory Servers, wireless networks.
Programming Languages:Shell Scripting, AppleScript
Schoun P. Regan is CEO of ITInstruction.com, which specializes in Mac OS X training and consulting. He speaks regularly to CEOs and CFOs on how to control IT department spending, the myths surrounding cross-platform integration, and the lunacy of expected lost revenue stemming from a culture bred to tolerate IT staff and operating system inadequacies as "normal". He seeks to change self-fulfilling IT departments that breed complacency for their jobs and contempt for the end user, neither of which are conducive to business.
