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.

 
AAPL
$102.05
Apple Inc.
+0.99
MSFT
$46.78
Microsoft Corpora
-0.28
GOOG
$585.83
Google Inc.
-1.55

MacTech Search:
Community Search:

Software Updates via MacUpdate

ScreenFlow 4.5.3 - Create screen recordi...
Save 5% with the MacUpdate coupon code: 68031AE15F -- Buy now! ScreenFlow is powerful, easy-to-use screencasting software for the Mac. With ScreenFlow you can record the contents of your entire... Read more
NeoOffice 2014.3 - Mac-tailored, OpenOff...
NeoOffice is a complete office suite for OS X. With NeoOffice, users can view, edit, and save OpenOffice documents, PDF files, and most Microsoft Word, Excel, and PowerPoint documents. NeoOffice 3.x... Read more
Typinator 6.2 - Speedy and reliable text...
Typinator turbo-charges your typing productivity. Type a little. Typinator does the rest. We've all faced projects that require repetitive typing tasks. With Typinator, you can store commonly used... Read more
PopChar X 6.7 - Floating window shows av...
PopChar X helps you get the most out of your font collection. With its crystal-clear interface, PopChar X provides a frustration-free way to access any font's special characters. Expanded... Read more
Evernote 5.6.0 - Create searchable notes...
Evernote allows you to easily capture information in any environment using whatever device or platform you find most convenient, and makes this information accessible and searchable at anytime, from... Read more
Monosnap 2.2.2 - Versatile screenshot ut...
Monosnap allows you to save screenshots easily, conveniently, and quickly, sharing them with friends and colleagues at once. It's the ideal choice for anyone who is looking for a smart and fast... Read more
Tunnelblick 3.4beta36 - GUI for OpenVPN...
Tunnelblick is a free, open source graphic user interface for OpenVPN on OS X. It provides easy control of OpenVPN client and/or server connections. It comes as a ready-to-use application with all... Read more
SoftRAID 5.0.4 - High-quality RAID manag...
SoftRAID allows you to create and manage disk arrays to increase performance and reliability. SoftRAID's intuitive interface and powerful feature set makes this utility a must have for any Mac OS X... Read more
Audio Hijack Pro 2.11.3 - Record and enh...
Audio Hijack Pro drastically changes the way you use audio on your computer, giving you the freedom to listen to audio when you want and how you want. Record and enhance any audio with Audio Hijack... Read more
Airfoil 4.8.9 - Send audio from any app...
Airfoil allows you to send any audio to AirPort Express units, Apple TVs, and even other Macs and PCs, all in sync! It's your audio - everywhere. With Airfoil you can take audio from any... Read more

Latest Forum Discussions

See All

Astropolo Review
Astropolo Review By Amy Solomon on September 23rd, 2014 Our Rating: Universal App - Designed for iPhone and iPad Astropolo is a space-themed children’s app with a great sense of style.   | Read more »
New E*TRADE Update Includes Touch ID and...
New E*TRADE Update Includes Touch ID and Home Screen Widget for iOS 8 Posted by Jessica Fisher on September 23rd, 2014 [ permalink ] | Read more »
Cupcake Carnival Review
Cupcake Carnival Review By Jennifer Allen on September 23rd, 2014 Our Rating: :: SAME OLDUniversal App - Designed for iPhone and iPad Cupcake Carnival does all the right match-3 things but it’s a format we’ve seen a little too... | Read more »
This Week at 148Apps: September 15-19, 2...
Expert App Reviewers   So little time and so very many apps. What’s a poor iPhone/iPad lover to do? Fortunately, 148Apps is here to give you the rundown on the latest and greatest releases. And we even have a tremendous back catalog of reviews; just... | Read more »
Kitty Powers’ Matchmaker – Tips, Tricks,...
Hey There, Kittens: | Read more »
Goblin Sword Review
Goblin Sword Review By Andrew Fisher on September 22nd, 2014 Our Rating: :: RETRO GOODNESSUniversal App - Designed for iPhone and iPad Fun visuals, good music, engaging level design, and lots of content make Goblin Sword an... | Read more »
Major New Update for CSR Racing Adds Fer...
Major New Update for CSR Racing Adds Ferrari and Multiplaye​r Posted by Jessica Fisher on September 22nd, 2014 [ permalink ] | Read more »
Veditor Review
Veditor Review By Jennifer Allen on September 22nd, 2014 Our Rating: :: PIMP YOUR VIDEOUniversal App - Designed for iPhone and iPad Want to add stickers and music to your videos? Veditor can do that easily.   | Read more »
1849′s Nevada Silver DLC is Still Search...
A few months ago, I took a look at 1849 from SomaSim. This Gold Rush-themed city builder for iPad had a fair bit going for it, but lacked in a few crucial areas to make it a true stand-out on the App Store. SomaSim has since added in a sandbox mode... | Read more »
Fruit Ninja Will be Reborn With a Massiv...
Fruit Ninja Will be Reborn With a Massive Update and Origins Animation Series Posted by Jessica Fisher on September 22nd, 2014 [ permalink ] Halfbrick Studios is rebuilding | Read more »

Price Scanner via MacPrices.net

Refurbished 2013 MacBook Pros available for u...
The Apple Store has Apple Certified Refurbished 13″ and 15″ MacBook Pros available starting at $929. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.5GHz MacBook Pros (4GB RAM/... Read more
New iPhones Score Big in SquareTrade Breakabi...
SquareTrade has announced the iPhone 6 and its larger sibling, iPhone 6 Plus, performed impressively in Breakability testing, and each carries the top Breakability Score in their respective category... Read more
10 Million + First Weekend Sales Set New iPho...
Apple has announced it sold over 10 million new iPhone 6 and iPhone 6 Plus models, a new record, just three days after the launch on September 19. iPhone 6 and iPhone 6 Plus are now available in the... Read more
Betty Crocker Launches New Cookbook for iOS
Betty Crocker, a General Mills brand, an established food industry leader, has announced its free digital cookbook app has been refreshed to make cooking with iPhone, iPad and iPod touch even easier... Read more
Apple restocks some refurbished 2014 MacBook...
The Apple Store has restocked some Apple Certified Refurbished 2014 MacBook Airs, with prices starting at $769. An Apple one-year warranty is included with each MacBook, and shipping is free. These... Read more
13-inch 128GB MacBook Air on sale for $949, s...
B&H Photo has the new 2014 13″ 1.4GHz/128GB MacBook Air on sale for $949.99 including free shipping plus NY tax only. Their price is $50 off MSRP. B&H will also include free copies of... Read more
Apple offering free $25 iTunes Gift Card with...
The Apple Store is offering a free $25 iTunes Gift Card with the purchase of a $99 Apple TV for a limited time. Shipping is free. Read more
Apple refurbished iPod touch available for up...
The Apple Store has Apple Certified Refurbished 5th generation iPod touches available starting at $149. Apple’s one-year warranty is included with each model, and shipping is free. Most colors are... Read more
iFixIt Tears Down iPhone 6; Awards Respectabl...
iFixit notes that even the smaller 4.7″ iPhone 6 is a giant among iPhones; so big that Apple couldn’t fit it into the familiar iPhone form factor. In a welcome reversal of a recent trend to more or... Read more
Phone 6 Guide – Tips Book For Both iPhone 6...
iOS Guides has announced its latest eBook: iPhone 6 Guide. Brought to you by the expert team at iOS Guides, and written by best-selling technology author Tom Rudderham, iPhone 6 Guide is packed with... Read more

Jobs Board

Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Position Opening at *Apple* - Apple (United...
…customers purchase our products, you're the one who helps them get more out of their new Apple technology. Your day in the Apple Store is filled with a range of Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** At the Apple Store, you connect business professionals and entrepreneurs with the tools they need in order to put Apple solutions to work in their Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.