TweetFollow Us on Twitter

MacEnterprise: Scripting Opportunities for System Administrators, Part One

Volume Number: 25
Issue Number: 06
Column Tag: MacEnterprise

MacEnterprise: Scripting Opportunities for System Administrators, Part One

When, where, why, and how you should run administrative scripts

By Greg Neagle, MacEnterprise.org

Introduction

In previous MacTech columns, I have sometimes offered up a script or two as part of a solution to a particular problem. Even if the script I presented is a perfect fit for your environment, you might still have had trouble making effective use of it in your organization, because you did not know how to make it run at the right time or in the correct context to get the job done.

This month, we'll begin a look at some of the many mechanisms available to run scripts (and other processes). Each mechanism has different uses and is suited for a unique set of tasks. Depending on what you need to accomplish, you should select the appropriate mechanism.

Why?

The first question you should ask is "Why do I want to run this script? What task do I want to accomplish?" Some of the common administrative categories that might lend themselves to scripting are:

System configuration - initial setup of the OS, networking, user accounts, etc.

System management - ongoing management of system settings; enforcing system-wide policies

User settings/preferences - configuring applications; setting up useful default preferences, enforcing user-level policies

Administrator tools - tools to make tedious or difficult tasks easier or more consistent

Hacks/fixes/workarounds - scripts to "fix" or work around problems with the OS or applications (or users!)

When?

Once you know why you are running the script, or what you want to accomplish with the script, you can consider when it should run. Some of the possibilities:

On demand - only when invoked by an admin or user

At startup

Repeating (daily/weekly/monthly, or other intervals like hourly, every 15 minutes, etc)

When a user logs in

When a user logs out

Let's look at some logical pairings of "Why?" and "When?":

Utility scripts or administrative tools that are to be run only on demand are the easiest to handle. Simply put them in a directory somewhere and run them manually as needed, or run them remotely using Apple Remote Desktop or SSH.

If your script is doing system configuration tasks like binding a machine to Active Directory or creating local users, it should almost certainly run at startup. System management tasks might run at startup, on a repeating schedule, or both.

Tasks that affect user settings or preferences should probably run at user login, or if it's a cleanup task, perhaps at user logout.

Hacks/fixes/workarounds can vary when it is appropriate to run them: they may need to run on demand; they may need to run at login to make a change to a user's environment; they may need to run at startup to clear out stale cached data.

How?

How can you run your script when you want? Let's look at some of the available mechanisms.

Running a script at startup

There are several ways to run scripts at startup, but the two most commonly used on Mac OS X are StartupItems and launchd items. Both Startup Items and launchd's LaunchDaemons run in the root context.

StartupItems

Startup items have been used on Mac OS X for a long time, and continue to work in OS X 10.5 Leopard. Administrator-provided Startup items should be placed in /Library/StartupItems. Since Apple is phasing out StartupItems, we won't spend a lot of time on these. A Startup Item consists of a directory containing an executable (typically a shell script) and a StartupParameters.plist file. Both the executable/shell script and the StartupParameters.plist have a very specific format. The startup item directory may optionally contain other items - for example, a Resources subdirectory. Apple has some good documentation on creating StartupItems here:

http://developer.apple.com/documentation/MacOSX/Conceptual/BPSystemStartup/Articles/StartupItems.html

launchd items

launchd was introduced with Mac OS X 10.4 Tiger. It was intended to replace almost every other way of launching processes, though in practice it has not yet accomplished that. Still, launchd is very capable, and Apple continues to enhance it. Launchd items are simpler to setup than StartupItems, as they generally require only a single additional file other than the actual script or executable. Administrator-provided launchd items that run a script at startup should go in /Library/LaunchDaemons.

Launchd has been covered extensively in MacTech as well as many other places, so I won't go into great depth. But let's do a quick example. Let's say we have a configuration script that we want to run at startup. It is located at /Library/Management/configuration.sh, and is marked as executable. It looks like this:

#!/bin/sh
logger -t configuration "Hello from the config script!"

This script simply writes a message to the system log. You can test it manually:

root# /Library/Management/configuration.sh
root# tail /var/log/system.log
<snip>
Apr 21 12:31:05 arcus configuration[8400]: Hello from the config script!

To get it to run at startup, you'd need a property list at /Library/LaunchDaemons/com.mactech.demo.plist that looks something like this:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
   <key>Label</key>
   <string>com.mactech.demo</string>
   <key>ProgramArguments</key>
   <array>
      <string>/Library/Management/configuration.sh</string>
   </array>
   <key>RunAtLoad</key>
   <true/>
   <key>OnDemand</key>
   <true/>
</dict>
</plist>

This property list should have owner: root, group: wheel, and mode: 0644. Some explanation of the included keys:

Label is a string used by launchd to identify the job. The name of the plist file is usually the same as this label plus ".plist".

ProgramArguments is simply the full path to the executable script.

RunAtLoad is set to true so that launchd will run the job when it loads it, which is normally at startup.

OnDemand is set to true so that launchd won't attempt to restart the script once it exits - in other words, this process/script is not meant to run continuously.

We could test the launchd job by rebooting and then looking at the system log for our message, but rebooting can take a while, and if there's a problem, the fix/retest cycle is tedious. So let's do a quicker test:

root# launchctl load /Library/LaunchDaemons/com.mactech.demo.plist
root# tail /var/log/system.log
<snip>
Apr 21 12:31:05 arcus configuration[8400]: Hello from the config script!
Apr 21 12:37:13 arcus configuration[9073]: Hello from the config script!

At the end of the system log, you should see the message from the configuration script.

If you have problems, unload the job:

root# launchctl unload /Library/LaunchDaemons/com.mactech.demo.plist

Make your changes to the plist, and try loading the job again. Once the job is working, you should be able to reboot, and see the message in the system log during the startup process.

Apple documentation on creating a launchd item is available here:

http://developer.apple.com/documentation/MacOSX/Conceptual/BPSystemStartup/Articles/LaunchOnDemandDaemons.html

Repeating scripts

Some scripts are best run on repeating intervals. For example, you have a script that scans the startup disk for all installed fonts and then uploads that list of fonts to a database somewhere so you can monitor for license compliance. You should run that script periodically: maybe daily, maybe weekly, maybe monthlyŃit's up to your organization. There are several ways to do this.

One of the easiest ways is to piggy-back off an existing facility for running repeating scripts: the periodic command. By default, periodic is used to run scripts on a daily, weekly or monthly basis. It runs all the scripts it finds in certain directories:

/etc/periodic/daily/ - these are run every day

/etc/periodic/weekly/ - these are run once a week

/etc/periodic/monthly/ - these are run once a month

To get periodic to run your scripts, mark them as executable and put them in the appropriate directory. You can control the order in which the scripts run by naming them appropriately. The convention used is to start the script name with a three-digit number; the scripts are then run in numeric order:

root# ls -1 /etc/periodic/daily
100.clean-logs
110.clean-tmps
130.clean-msgs
430.status-rwho
500.daily
599.randomSleep
600.updateMachineName
700.updateHostInfo
900.autoradmind

There are some issues to be aware of, however. The first is exactly when these scripts will run. This is controlled by launchd in the following files in /System/Library/LaunchDaemons:

com.apple.periodic-daily.plist
com.apple.periodic-monthly.plist
com.apple.periodic-weekly.plist

Looking at com.apple.periodic-daily.plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
   <key>Label</key>
   <string>com.apple.periodic-daily</string>
   <key>ProgramArguments</key>
   <array>
      <string>/usr/sbin/periodic</string>
      <string>daily</string>
   </array>
   <key>LowPriorityIO</key>
   <true/>
   <key>Nice</key>
   <integer>1</integer>
   <key>StartCalendarInterval</key>
   <dict>
      <key>Hour</key>
      <integer>3</integer>
      <key>Minute</key>
      <integer>15</integer>
   </dict>
</dict>
</plist>

The StartCalendarInterval key tells us it will run each day at 3:15 AM local time. That time might not be a good one for your environment. Consider a few scenarios:

Desktop machines: if the desktops in your organization are left on 24/7, then the script will run shortly after 3:15 AM each day. If instead, they are asleep at 3:15 AM, they'll run shortly after they are woken up each day. If they are powered off at 3:15 AM, the scripts won't run at all. Launchd will reschedule jobs that were scheduled to run when the machine was asleep, but will not reschedule jobs that were scheduled to run when the machine was powered off.

Laptop machines: all of the same complications as with desktops, with the additional problem that if they get taken home at night or over the weekend, and run these jobs at 3:15 AM (or when woken up), and your scripts require access to network services or resources available only when the machine is connected to your organization's network, they may fail, or at the very least, fail to do anything useful.

Therefore, you might consider changing the time these jobs run to a time during the day when it's more likely the machine is on, awake, and on your network.

Another possible approach that does not require modifying Apple's provided launchd items is to run a script at startup that checks for overdue periodic jobs and runs them. Such a script is described (and available) here:

http://managingosx.wordpress.com/2008/06/18/launchd-vs-periodic/

Repeating launchd jobs

Looking at the property list for com.apple.periodic-daily.plist suggests another method for running scripts on a repeating basis: avoiding the periodic middleman and using launchd directly. Using our com.mactech.demo example as before, we can run a script at startup and once a day with a LaunchDaemon plist like this:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
   <key>Label</key>
   <string>com.mactech.demo</string>
   <key>ProgramArguments</key>
   <array>
      <string>/Library/Management/configuration.sh</string>
   </array>
   <key>RunAtLoad</key>
   <true/>
   <key>OnDemand</key>
   <true/>
   <key>StartCalendarInterval</key>
   <dict>
      <key>Hour</key>
      <integer>12</integer>
      <key>Minute</key>
      <integer>15</integer>
   </dict>
</dict>
</plist>

We've added a StartCalendarInterval to the previous version of the property list that tells launchd to run the job each day at 12:15, when many of our staff will be at lunch. If we didn't want it to run at startup as well, we could remove the RunAtLoad key, or set it to false.

Good old cron

One last method to mention: the classic UNIX cron is still available in OS X, and can still be used to run repeating jobs. Type man cron at a command prompt for details. You'll probably want to create a crontab at /etc/crontab . A big disadvantage of using cron is that it's hard to manage different versions of the crontab files. For example, if you have a set of machines that need repeating jobs A and B, another set that needs repeating jobs B and C, and yet another set that needs repeating jobs A, B and C, you'll need to manage three different versions of the crontab as well as the scripts that do the actual jobs. If you use periodic or launchd, you don't have to deal with the monolithic crontab file, as the scheduling info for each job lives in a separate file (or in the case of periodic, is not needed).

To be continued...

We covered quite a bit this month. We looked at running scripts at startup and on a repeating schedule. In the future, we'll look at running scripts as part of the login and logout process, both with root privileges, and as the user logging-in. While you might guess that launchd might be useful here, we'll also look at login/logout hooks and login items. We'll also consider the special case of scripts that should run only once, either at startup or login. Finally, we'll look at some methods to simplify implementing additional scripts once you have a few working. See you next time!


Greg Neagle is a member of the steering committee of the Mac OS X Enterprise Project (macenterprise.org) and is a senior systems engineer at a large animation studio. Greg has been working with the Mac since 1984, and with OS X since its release. He can be reached at gregneagle@mac.com.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

calibre 2.17 - Complete e-library manage...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
OmniGraffle Pro 6.1.2 - Create diagrams,...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
OmniGraffle 6.1.2 - Create diagrams, flo...
OmniGraffle helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use Graffle to... Read more
RoboForm 2.0.2 - Password manager; syncs...
RoboForm is a password manager that offers one-click login, mobile syncing, easy form filling, and reliable security. Password Manager. RoboForm remembers your passwords so you don't have to! Just... Read more
Apple MainStage 3.1 - Live performance t...
Love the sound you got on your recording? MainStage 3 makes it easy to bring all the same instruments and effects to the stage. Everything from the Sound Library and Smart Controls you're familiar... Read more
Freeway Pro 7.0.2 - Drag-and-drop Web de...
Freeway Pro lets you build websites with speed and precision... without writing a line of code! With its user-oriented drag-and-drop interface, Freeway Pro helps you piece together the website of... Read more
A Better Finder Rename 9.44 - File, phot...
A Better Finder Rename is the most complete renaming solution available on the market today. That's why, since 1996, tens of thousands of hobbyists, professionals and businesses depend on A Better... Read more
Stacks 2.6.9 - New way to create pages i...
Stacks is a new way to create pages in RapidWeaver. It's a plugin designed to combine drag-and-drop simplicity with the power of fluid layout. Features: Fluid Layout: Stacks lets you build pages... Read more
Sid Meier's Civilization: Beyond Ea...
Sid Meier's Civilization: Beyond Earth is a new science-fiction-themed entry into the award-winning Civilization series. Set in the future, global events have destabilized the world leading to a... Read more
Logic Pro X 10.1 - Music creation and au...
Apple Logic Pro X is the most advanced version of Logic ever. Sophisticated new tools for professional songwriting, editing, and mixing are built around a modern interface that's designed to get... Read more

Choice Provisions is Set to Launch Destr...
Choice Provisions is Set to Launch Destructamundo on iOS This Month Posted by Tre Lawrence on January 23rd, 2015 [ permalink ] Choice Provisions – home stable to | Read more »
King of Thieves – An Interview With Zept...
Ahead of the release of ZeptoLab’s King of Thieves, we were able to ask ZeptoLab’s co-founder, Semyon Voinov, a few questions about the inspiration behind the game and what that means for the Cut the Rope franchise. | Read more »
Handle Review
Handle Review By Jennifer Allen on January 23rd, 2015 Our Rating: :: SPEEDY ORGANIZINGUniversal App - Designed for iPhone and iPad Handle is a very convenient way of juggling your emails, To Do list, and Calendar all through one... | Read more »
The New Disney Inquizitive App Offers a...
The New Disney Inquizitive App Offers a Place for Fans to Take Disney Quizzes Posted by Tre Lawrence on January 23rd, 2015 [ permalink ] | Read more »
Hands-On With Cut the Rope Developer Zep...
Marking quite a departure from ZeptoLab’s past successes, namely the Cut The Rope series, King of Thieves is shaping up to be quite promising. Due for release in February, we were lucky enough to have some time with a preview build to see exactly... | Read more »
Fast Fishing Review
Fast Fishing Review By Jennifer Allen on January 23rd, 2015 Our Rating: :: LIVES UP TO ITS NAMEUniversal App - Designed for iPhone and iPad Fishing is far from relaxing in Fast Fishing, but it is fun.   | Read more »
The LEGO Movie Video Game is Available N...
The LEGO Movie Video Game is Available Now for iOS Posted by Ellis Spice on January 23rd, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Satellina Review
Satellina Review By Jennifer Allen on January 23rd, 2015 Our Rating: :: TWITCHY BUT TACTICALUniversal App - Designed for iPhone and iPad Satellina requires quick thinking and twitchy fingers, and it’s pretty fun.   | Read more »
Tail Drift, the Crazy 360 Degree Flyer,...
Tail Drift, the Crazy 360 Degree Flyer, Has Gone Free-to-Play in a New Update Posted by Jessica Fisher on January 22nd, 2015 [ permalink ] | Read more »
PureSkate 2 Review
PureSkate 2 Review By Tre Lawrence on January 22nd, 2015 Our Rating: :: ALMOST ALL AIRUniversal App - Designed for iPhone and iPad PureSkate 2 lets one’s fingers do the skateboarding.   | Read more »

Price Scanner via MacPrices.net

College Student Deals are back, additional $5...
Take an additional $50 off all MacBooks and iMacs at Best Buy Online with their College Students Deals Savings, valid through April 11, 2015. Anyone with a valid .EDU email address can take advantage... Read more
iPhone 6 and 6 Plus GIve Apple Half Of US Mob...
Chicago-based Consumer Intelligence Research Partners, LLC (CIRP) have released analysis of the results of its research on mobile phone manufacturers for the calendar quarter that ended December 31,... Read more
Save $100 on MacBook Airs with 256GB of stora...
B&H Photo has 256GB MacBook Airs on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 1.4GHz/256GB MacBook Air: $999 $100 off MSRP - 13″ 1.4GHz/256GB MacBook... Read more
21-inch 2.7GHz iMac on sale for $1179, save $...
B&H Photo has the 21″ 2.7GHz iMac on sale for $1179 including free shipping plus NY sales tax only. Their price is $120 off MSRP, and it’s the lowest price available for this model from any... Read more
iPhone Usage Rates by State Correlate With Ed...
Chitika Insights notes that despite iPhones being the largest source of smartphone Internet traffic in North America, their latest study finds a relatively high degree of variation of iPhone usage... Read more
ProGearX Extendable Pole “Pov/Selfie Stick” M...
There’s something inescapably narcissistic about the concept of selfies as they’ve developed as a smartphone-driven social (particularly social media) phenomenon that rubs me the wrong way. However,... Read more
iPad Air 2 on sale for up to $100 off MSRP, 2...
 Best Buy has iPad Air 2s on sale for up to $100 off MSRP on their online store for the next two days. Choose free shipping or free local store pickup (if available). Sale prices available for online... Read more
Roundup of Apple refurbished MacBook Pros and...
The Apple Store has Apple Certified Refurbished 2014 MacBook Pros and MacBook Airs available for up to $400 off the cost of new models. An Apple one-year warranty is included with each model, and... Read more
Sale! 13-inch 2.8GHz Retina MacBook Pro for $...
 B&H Photo has the 13″ 2.8GHz Retina MacBook Pro on sale for $1599 including free shipping plus NY sales tax only. Their price is $200 off MSRP, and it’s the lowest price available for this model... Read more
Next OS X/iOS Version Upgrades Should Concent...
On stage at Apple’s World Wide Developers’ Conference in June 2009, Bertrand Serlet, the company’s Senior Vice President of Software Engineering at the time, announced that the forthcoming OS X... Read more

Jobs Board

*Apple* Solutions Consultant (ASC)- Retail S...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
*Apple* Lead Operator, GSOC - Apple (United...
**Job Summary** Apple is seeking an exceptional, customer service oriented and experienced persons to fulfill the role of Apple Lead Operator (ALO) as part of the Read more
Order Support Supervisor- *Apple* Online Sto...
**Job Summary** The Apple Online Store (AOS) Order Administration team is looking for an Order Support Supervisor to manage and lead a team of Specialists through the Read more
Senior Program Manager, *Apple* Online Supp...
**Job Summary** The Apple Online Support Planning team is looking for an experienced Senior Project Manager to lead key Quality program initiatives across the Online Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.