TweetFollow Us on Twitter

MacEnterprise: Scripting opportunities for System Administrators, part 2

Volume Number: 25
Issue Number: 07
Column Tag: MacEnterprise

MacEnterprise: Scripting opportunities for System Administrators, part 2

Running administrative scripts at login and logout, and more

By Greg Neagle, MacEnterprise.org

Introduction

In an earlier issue of MacTech, we started a look at scripting opportunities for systems administrators. We talked about why you might want to run a script, when it's possible and advisable to run scripts for certain tasks, and began to look at exactly how you get your scripts to run at the right time.

Previously, we discussed running scripts at startup and on a repeating schedule. This month, we'll look at running scripts as part of the login and logout process, both with root privileges, and as the user logging in. We'll also consider 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.

Login/Logout hooks

A very common administrative need is to run a script (or scripts) when a user logs in or when a user logs out. One possible reason to do this is that you need to make a change to the user's environment: maybe you need to redirect a network user's caches to the local disk before they complete their login, or you need to do some cleanup on logout.

If you need to run a script at each user login, and the script must have superuser (root) privileges, you should consider implementing a login hook. A login hook is a script that runs as part of the login process. It runs after the user's home directory has been mounted (if it's a network user or one whose home directory has been protected with FileVault). It runs as root, but is passed the name of the user who is logging in.

To set up a login hook, make sure your script is executable:

sudo chmod 755 /path/to/script

Then set the loginhook:

sudo defaults write com.apple.loginwindow LoginHook /path/to/script

Log out and back in, and the hook should run. Logout hooks are set up similarly:

sudo defaults write com.apple.loginwindow LogoutHook /path/to/script

Here's an example of a script that could be used as a logout hook. On logout, it randomly selects a picture to use as the desktop picture/background behind the loginwindow.

#!/usr/bin/perl -w
use strict;
my $loginwindowprefs = "/Library/Preferences/com.apple.loginwindow";
my $picdir = "/Library/Desktop Pictures/Nature";
if ( -d "$picdir") {
   my @list = split("\n",`ls -1 "$picdir"`);
   my @pictures = ();
   
   for my $item (@list) {
      if (-f "$picdir/$item") {
         push @pictures, "$picdir/$item";
      }
   }
   
   if (scalar(@pictures)) {
      my $currentpicture = `/usr/bin/defaults read $loginwindowprefs DesktopPicture`;
      if ($currentpicture) { chomp($currentpicture) };
      my $randompicture = $currentpicture;
   
      while ($randompicture eq $currentpicture) {
         my $randomindex = int(rand(scalar(@pictures)));
         $randompicture = $pictures[$randomindex];
      }
   
      my $result = `/usr/bin/defaults write $loginwindowprefs DesktopPicture "$randompicture"`;
   }
}


Figure 1. MCX login scripts

Each time a user logs out, the picture behind the loginwindow is changed. Since this script runs during logout, but before the loginwindow is displayed, you should see a new picture at each logout.

Apple's Knowledge Base article on setting up a login hook is here: http://support.apple.com/kb/HT2420

MCX login scripts

There is another way to specify a specific script to run at login or logout, and that is using MCX via Workgroup Manager (Figue 1, above).

Using MCX to manage login scripts requires very specific client settings and can be tricky to get right. Make sure to read the relevant help information, accessible by clicking the purple question mark in Workgroup Manager.

Other login options

Login hooks run as the root user. There are tasks that require running as the user logging in. For these, you have a few options:

Use a login hook, but within the hook, act as the user with the su command. This can be tricky to get right.

Implement it as a launchd LaunchAgent.

Write your script as a launchable application and add it to the login items.

LaunchAgents

LaunchAgents had some pretty serious shortcomings in Tiger, but in Leopard, they are pretty useful.

A LaunchAgent is started when a user logs in, and runs as that user. As the system administrator, you should put LaunchAgent plists in /Library/LaunchAgents. /System/Library/LaunchAgents is reserved for use by Apple, and ~/Library/LaunchAgents is for the user's personal use.

Let's say you wanted to run a script at user login that would launch a setup assistant-type application - a LaunchAgent would be a good fit for this. Here's an example plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>Label</key>
        <string>org.mactech.demolaunchagent</string>
        <key>LimitLoadToSessionType</key>
        <string>Aqua</string>
        <key>Program</key>
        <string>/Library/Management/runSetupAssistant.pl</string>
        <key>RunAtLoad</key>
        <true/>
</dict>
</plist>

This LaunchAgent plist has a unique label, which is simply a name for the task. A new key introduced in 10.5 Leopard is LimitLoadToSessionType, and here it is set to Aqua. This tells launchd to load the job only when there is a GUI login - if the user were to login via SSH, for example, the job would not run. This makes sense for this, as we wouldn't want our GUI setup assistant application to run if the user wasn't logging into the GUI console. If you had a job that made sense to run only for a non-GUI login, you would set the value of LimitLoadToSessionType to StandardIO. Finally, the RunAtLoad key is set to true to tell launchd to run the script immediately when loading the job after login.

For more information about LaunchAgents and their options, see this Apple Technical Note: http://developer.apple.com/technotes/tn2005/tn2083.html

Last time I promised that I'd cover scripts that should run only once. A classic case is a script that launches a setup assistant. You might want it to launch the assistant the first time a user logs in, but you probably don't want it to launch every time the user logs in. Here's how you might handle this:

#!/usr/bin/perl
#run the Setup Assistant if it's never run before
$homedir = $ENV{'HOME'};
$checkFile = "$homedir/.my.org.setupassistant";
unless (-f "$checkFile") {
   `touch $checkFile`;
   `open "/Applications/Utilities/My Org Setup Assistant.app"`;
}

Here's what's happening. We define a filename - ".my.org.setupassistant". We start the name with a period so it is invisible in the Finder. The script checks for the existence of the file in the root of the current user's home directory. If it's not present, the script creates the file and opens the Setup Assistant. The next time the script runs for this user, the file will exist, and the script will exit without opening the Setup Assistant.

You can use this same basic technique for any script you want to run just once - the script actually runs at each startup/login/etc, but exits without doing anything if a certain file exists. In my opinion, this is a better approach than a script that removes itself after it runs because you can easily re-run the script in the future simply by removing its "flag" file.

Login items

There is another type of item that runs at user login. It's usually referred to as a login item, though an earlier version of Mac OS X confusingly called these "startup items". Users can add their own login items, either from the Accounts pane of the System Preferences application, or by right-clicking or control-clicking on an item in the Dock and choosing Open at Login from the contextual menu that appears.


Figure 2. Setting an item to open at login

What a system administrator needs, though, is a way to specify that certain items open for all users of a given machine. There are two ways to do this. The first, if you are using MCX, is to add the items to the managed login preferences using Workgroup Manager. The second is to add the items to the file at /Library/Preferences/loginwindow.plist:

> defaults read /Library/Preferences/loginwindow AutoLaunchedApplicationDictionary
(
        {
        Hide = 1;
        Path = "/Library/Management/LoginLauncher.app";
    }
)

Applications added here are launched for all users of a given machine at login, in addition to whatever items a user may have added to their own list of login items. Note that the name of the key is AutoLaunchedApplicationDictionary - you have to add applications here, and not scripts - even if they are set as executable. In order to use this mechanism to run scripts, you need to either wrap your script into an application bundle, or write an app whose purpose is to run your scripts. Fortunately, I've done that work for you. A link to such an application can be found in the next section of this article.

Running multiple scripts

A major problem with login/logout hooks is that there is support for only a single login/logout script. This can be a problem if you need to implement more than one script. A solution to this problem is to implement master login/logout hooks, which in turn run additional scripts within a given directory. Here's a sample master login hook:

#!/bin/sh
# Master login hook script
# runs each script found in the login hooks directory
LOGINHOOKSDIR="/etc/hooks/login"
if [ -d ${LOGINHOOKSDIR} ]; then
    for script in ${LOGINHOOKSDIR}/* ; do
        if [ -s ${script} -a -x ${script} ]; then
            # log this run
            logger -s -t LoginHook -p user.info Executing ${script}... 1>&2
            # run the item.
            ${script} $*
             
            # if there was an error, log it
            rc=$?
            if [ $rc -ne 0 ]; then
                logger -s -t LoginHook -p user.info ${script} failed with return code ${rc} 1>&2
                exit $rc
             fi
        fi
    done
fi
exit 0

This master hook loops through all the items in the /etc/hooks/login directory, checks to see if each item is non-zero-length and executable, and if so, writes a message to the system log announcing it's running the item, and then runs the item, passing along any command-line parameters that were sent to the master hook. A similar script could be used to run multiple logout hooks.

In fact, this technique is useful in other scripting situations. If you create a launchd plist to run a specific script at startup, and later you want to run another script as well, you'd have to create another launchd plist for the second script. This quickly gets tedious and error-prone. If, instead, you created a script like the master loginhook that ran all the scripts in a certain directory, and created a launchd plist to run that script, then to run additional scripts, you'd only have to put them in the special directory. This enables you to do the hard work once and then add or subtract scripts as needed.

Another variation of this technique can be used to run scripts at login as the user who is logging in. You can get details on doing this at the MacEnterprise.org site:

http://www.macenterprise.org/articles/runningitemsatlogin

Conclusion, and More info

That concludes our look at scripting opportunities. You should now have a better idea how you can get your scripts to run at the proper time and in the proper context. Below, I've listed a few more places to get more info on some of the topics we've discussed. Good luck!

More options for running code at login, and a discussion of the pros and cons of each:

http://developer.apple.com/technotes/tn2008/tn2228.html

launchd, LaunchDaemons, and LaunchAgents:

http://developer.apple.com/technotes/tn2005/tn2083.html

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

Login items, login/logout hooks, and LaunchAgents:

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


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

Apple High Sierra 10.13 - The latest OS...
macOS High Sierra introduces new core technologies that improve the most important functions of your Mac. From rearchitecting how it stores your data to improving the efficiency of video streaming to... Read more
ScreenFlow 7.1 - Create screen recording...
ScreenFlow is powerful, easy-to-use screencasting software for the Mac. With ScreenFlow you can record the contents of your entire monitor while also capturing your video camera, microphone and your... Read more
Airmail 3.5 - Powerful, minimal email cl...
Airmail is an mail client with fast performance and intuitive interaction. Support for iCloud, MS Exchange, Gmail, Google Apps, IMAP, POP3, Yahoo!, AOL, Outlook.com, Live.com. Airmail was designed... Read more
CleanMyMac 3.9.0 - $39.95
CleanMyMac makes space for the things you love. Sporting a range of ingenious new features, CleanMyMac lets you safely and intelligently scan and clean your entire system, delete large, unused files... Read more
Numi 3.17.2 - Menu-bar calculator suppor...
Numi is a calculator that magically combines calculations with text, and allows you to freely share your computations. Numi combines text editor and calculator Support plain English. For example, '5... Read more
OmniGraffle 7.4.3 - 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
ExpanDrive 6.1.0 - Access cloud storage...
ExpanDrive builds cloud storage in every application, acts just like a USB drive plugged into your Mac. With ExpanDrive, you can securely access any remote file server directly from the Finder or... Read more
VueScan 9.5.86 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Cocktail 11.0 - General maintenance and...
Cocktail is a general purpose utility for macOS that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
OmniGraffle Pro 7.4.3 - 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

Morphite guide - how to explore like a p...
The much anticipated space exploration game, Morphite, has finally arrived, and we can't get enough of it. The game is essentially everything we wanted No Man's Sky to be. It's a game that puts a heavy focus on exploring foreign worlds, but the... | Read more »
The best visual novels on mobile
Narrative games have been around for ages, but only now have they been creeping into the mainstream spotlight. These games tell some of the industry's finest stories, and they break new ground in terms of gameplay and mechanics regularly. Here are... | Read more »
The best new games we played this week -...
It's pretty much been one big release after another. We were privy to a bunch of surprises this week, with a lot of games we'd been waiting for quite some time dropping unexpectedly. We hope you're free this weekend, because there is a lot for... | Read more »
Stormbound: Kingdom Wars guide - how to...
Stormbound: Kingdom Wars is an excellent new RTS turned card battler out now on iOS and Android. Lovers of strategy will get a lot of enjoyment out of Stormbound's chess-like mechanics, and it's cardbased units are perfect for anyone who loves the... | Read more »
The best AR apps and games on iOS right...
iOS 11 has officially launched, and with it comes Apple's ARKit, a helpful framework that makes it easier than ever for developers to create mobile AR experiences. To celebrate the occassion, we're featuring some of the best AR apps and games on... | Read more »
Phoenix Wright: Ace Attorney - Spirit of...
Phoenix Wright: Ace Attorney - Spirit of Justice 1.00.00 Device: iOS Universal Category: Games Price: $.99, Version: 1.00.00 (iTunes) Description: ************************************************※IMPORTANT※・Please read the “When... | Read more »
Kpressor (Utilities)
Kpressor 1.0.0 Device: iOS Universal Category: Utilities Price: $4.99, Version: 1.0.0 (iTunes) Description: The ultimate ZIP compression application for iPhone and iPad. - Full integration of iOS 11 with support for multitasking.-... | Read more »
Find out how you can save £35 and win a...
Nothing raises excitement like a good competition, and we’re thrilled to announce our latest contest. We’ll be sending one lucky reader and a friend to the Summoners War World Arena Championship at Le Comedia in Paris on October 7th. It’s the... | Read more »
Another Lost Phone: Laura's Story...
Another Lost Phone: Laura's Story 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Another Lost Phone is a game about exploring the social life of a young woman whose phone you have just... | Read more »
The Witness (Games)
The Witness 1.0 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0 (iTunes) Description: You wake up, alone, on a strange island full of puzzles that will challenge and surprise you. You don't remember who you are, and... | Read more »

Price Scanner via MacPrices.net

Snag a Certified Refurbished Apple Pencil for...
Apple has Certified Refurbished Apple Pencils available for $85 including free shipping. Their price is $14 off MSRP, and it’s the lowest price available for a Pencil. Read more
12-inch 64GB iPad Pro on sale for $749, save...
Adorama has 12″ 64GB iPad Pros on sale today for $749 including free shipping plus NY & NJ sales tax only. Their price is $50 off MSRP. Read more
Apple Certified Refurbished iPad minis availa...
Apple has Certified Refurbished 128GB iPad minis available today for $339 including free shipping. Apple’s standard one-year warranty is included. Their price is $60 off MSRP. Read more
12-inch 1.2GHz Retina MacBook Pros on sale fo...
B&H Photo has 2017 12″ 1.2GHz Retina MacBooks on sale for $100 off MSRP. Shipping is free, and B&H charges sales tax in NY & NJ only: 12″ 1.2GHz Space Gray MacBook: $1199 $100 off MSRP 12... Read more
Sunday sale: 13-inch 3.1GHz MacBook Pros for...
Amazon has 2017 13″ 3.1GHz MacBook Pros on sale today for up to $150 off MSRP, each including free shipping: – 13″ 3.1GHz/256GB Space Gray MacBook Pro (MPXV2LL/A): $1649.99 $150 off MSRP – 13″ 3.1GHz... Read more
Looking for a 2017 12″ Retina MacBook? Save $...
Apple has Certified Refurbished 2017 12″ Retina MacBooks available for $200-$240 off the cost of new models. Apple will include a standard one-year warranty with each MacBook, and shipping is free.... Read more
Apple Offering Up To $455 Credit Toward iPhon...
iPhone 8 and 8 Plus are now available at the Apple Store, and you can receive up to $375 credit toward a new iPhone purchase when you trade in your eligible smartphone. Photo Courtesy Apple Just... Read more
AnyTrans Offers iOS Users Three Ways For Movi...
iMobie Inc. today announceed AnyTrans v6.0.1, which now can help iOS users move all data to iPhone 8/8 Plus seamlessly. The software is available both on Mac and Windows and fully able to move all... Read more
Snag a 13-inch 2.3GHz MacBook Pro for $100 of...
B&H Photo has 2017 13″ 2.3GHz MacBook Pros in stock today and on sale for $100 off MSRP, each including free shipping plus NY & NJ sales tax only: – 13-inch 2.3GHz/128GB Space Gray MacBook... Read more
Verizon offers new iPhone 8 for $100-$300 off...
Verizon is offering the new iPhone 8 for up to $300 off MSRP with an eligible trade-in: • $300 off: iPhone 6S/6S Plus/7/7 Plus, Google Pixel XL, LG G6, Moto Z2 Force, Samsung Galaxy S7/S7 edge/S8/S8... Read more

Jobs Board

Development Operations and Site Reliability E...
Development Operations and Site Reliability Engineer, Apple Payment Gateway Job Number: 57572631 Santa Clara Valley, California, United States Posted: Jul. 27, 2017 Read more
Data Engineer - *Apple* Media Products - Ap...
Job Summary Apple is seeking a highly skilled data engineer to join the Data Engineering team within Apple Media Products. AMP (home to Apple Music, App Read more
Development Operations and Site Reliability E...
Development Operations and Site Reliability Engineer, Apple Payment Gateway Job Number: 57572631 Santa Clara Valley, California, United States Posted: Jul. 27, 2017 Read more
Development Operations and Site Reliability E...
Development Operations and Site Reliability Engineer, Apple Payment Gateway Job Number: 57572631 Santa Clara Valley, California, United States Posted: Jul. 27, 2017 Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.