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

ExpanDrive 4.3.2 - 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
RapidWeaver 6.0.8 - Create template-base...
RapidWeaver is a next-generation Web design application to help you easily create professional-looking Web sites in minutes. No knowledge of complex code is required, RapidWeaver will take care of... Read more
Artlantis Studio 5.1.2.7 - 3D rendering...
Artlantis Studio is a unique and ideal tool for performing very high resolution rendering easily and in real time. The new FastRadiosity engine now lets you compute images in radiosity-even in... Read more
MacUpdate Desktop 6.0.5 - Search and ins...
MacUpdate Desktop 6 brings seamless 1-click installs and version updates to your Mac. With a free MacUpdate account and MacUpdate Desktop 6, Mac users can now install almost any Mac app on macupdate.... Read more
BitTorrent Sync 2.0.82 - Sync files secu...
BitTorrent Sync allows you to sync unlimited files between your own devices, or share a folder with friends and family to automatically sync anything. File transfers are encrypted. Your information... Read more
Google Drive 1.20 - File backup and shar...
Google Drive is a place where you can create, share, collaborate, and keep all of your stuff. Whether you're working with a friend on a joint research project, planning a wedding with your fiancé, or... Read more
Simon 4.0.3 - Monitor changes and crashe...
Simon monitors websites and alerts you of crashes and changes. Select pages to monitor, choose your alert options, and customize your settings. Simon does the rest. Keep a watchful eye on your... Read more
Vitamin-R 2.23 - Personal productivity t...
Vitamin-R creates the optimal conditions for your brain to work at its best by structuring your work into short bursts of distraction-free, highly focused activity alternating with opportunities for... Read more
iDefrag 5.0.0 - Disk defragmentation and...
iDefrag helps defragment and optimize your disk for improved performance. Features include: Supports HFS and HFS+ (Mac OS Extended). Supports case sensitive and journaled filesystems. Supports... Read more
PCalc 4.2 - Full-featured scientific cal...
PCalc is a full-featured, scriptable scientific calculator with support for hexadecimal, octal, and binary calculations, as well as an RPN mode, programmable functions, and an extensive set of unit... Read more

Warner Bros. Interactive Entertainment A...
Warner Bros. has some exciting games coming down the pipe! | Read more »
GDC 2015 – Star Trek Timelines will Prob...
GDC 2015 – Star Trek Timelines will Probably Make Your Inner Trekkie Squeal With Glee Posted by Rob Rich on March 4th, 2015 [ permalink ] Any popular fictional universe has its fair share of fan fiction – where belo | Read more »
Protect Yourself from an Onslaught of Ca...
Surprise Attack Games has announced a Cat-astrophic new physics puzzler called Fort Meow! In the game, a young girl named Nia finds her grandfather’s journal which triggers an all mighty feline attack! Why do the cats want the journal? Who knows,... | Read more »
GDC 2015 – Jelly Reef will be Game Oven’...
GDC 2015 – Jelly Reef will be Game Oven’s Last Hurrah, and it Seems like a Good Note to Go Out on Posted by Rob Rich on March 4th, 2015 [ permalink ] It’s sad knowing that Game Oven ( | Read more »
daWindci Deluxe Review
daWindci Deluxe Review By Campbell Bird on March 4th, 2015 Our Rating: :: BLUSTERY PUZZLESUniversal App - Designed for iPhone and iPad This updated puzzle game offers some creative gameplay and new mechanics, but still suffers from... | Read more »
Dungeon Hunter 5 Coming on March 12
Gameloft has excitedly announced that Dungeon Hunter 5 is on its way! Once again, you will adventure across the land of Valenthia exploring dungeons and fighting monsters. The game will have a new asynchronous multiplayer mode called Strongholds... | Read more »
GDC 2015 – The Sandbox 2 is Coming, and...
GDC 2015 – The Sandbox 2 is Coming, and Now it has Textures! | Read more »
Warner Bros. Interactive Announces Mort...
Mortal Kombat X, by Warner Bros. and NetherRealm Studios, will be a a free-to-play fighting/card-battle Mortal Kombat game. The game promises card collecting, multiplayer team combat, classic characters such as Scorpion, Sub-Zero and Raiden, and the... | Read more »
GDC 2015 – Piloteer is Whitaker Trebella...
GDC 2015 – Piloteer is Whitaker Trebella’s Latest Project, and it’s Definitely Something DIfferent Posted by Rob Rich on March 3rd, 2015 [ permalink ] You know | Read more »
PangoLand Review
PangoLand Review By Amy Solomon on March 3rd, 2015 Our Rating: :: COME VISIT PANGO AND FRIENDSUniversal App - Designed for iPhone and iPad PangoLand is an open-ended world full of familiar characters, bright colors and interactive... | Read more »

Price Scanner via MacPrices.net

iPad: A More Positive Outlook – The ‘Book Mys...
It’s good to hear someone saying positive things about the iPad. I’ve been trying to bend my mind around how Apple’s tablet could have gone from zero to bestselling personal computing device on the... Read more
Mac Pros on sale for up to $279 off MSRP
Amazon has Mac Pros in stock and on sale for up to $279 off MSRP. Shipping is free: - 4-Core Mac Pro: $2725.87, $273 off MSRP (9%) - 6-Core Mac Pro: $3719.99, $279 off MSRP (7%) Read more
Sale! 13-inch Retina MacBook Pros for up to $...
B&H Photo has 13″ Retina MacBook Pros on sale for up to $205 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.6GHz/128GB Retina MacBook Pro: $1219.99 save $80 - 13″ 2.... Read more
Another Tranche Of IBM MobileFirst For iOS Ap...
IBM has announced the next expansion phase for  its IBM MobileFirst for iOS portfolio, with a troika of new apps to address key priorities for the Banking and Financial Services, Airline and Retail... Read more
Sale! 15-inch Retina MacBook Pros for up to $...
B&H Photo has the new 2014 15″ Retina MacBook Pros on sale for up to $250 off MSRP for a limited time. Shipping is free, and B&H charges NY sales tax only: - 15″ 2.2GHz Retina MacBook Pro: $... Read more
WaterField Designs Introduces the Minimalist...
With Apple Pay gaining popularity, Android Pay coming in May 2015, and loyalty cards and receipts that can be accessed from smartphones, San Francisco’s WaterField Designs observes that it may be... Read more
Sale! 15-inch 2.2GHz Retina MacBook Pro for $...
 Best Buy has the 15″ 2.2GHz Retina MacBook Pro on sale for $1774.99 $1799.99, or $225 off MSRP. Choose free home shipping or free local store pickup (if available). Price valid for online orders... Read more
13-inch 2.5GHz MacBook Pro (refurbished) avai...
The Apple Store has Apple Certified Refurbished 13″ 2.5GHz MacBook Pros available for $170 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.5GHz... Read more
13-inch 2.5GHz MacBook Pro on sale for $100 o...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $999.99 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more
27-inch 3.5GHz 5K iMac in stock today and on...
 B&H Photo has the 27″ 3.5GHz 5K iMac in stock today and on sale for $2299 including free shipping plus NY sales tax only. Their price is $200 off MSRP, and it’s the lowest price available for... Read more

Jobs Board

*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
*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
Position Opening at *Apple* - Apple (United...
…Summary** As a Specialist, you help create the energy and excitement around Apple products, providing the right solutions and getting products into customers' hands. You Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** The Apple Store is a retail environment like no other - uniquely focused on delivering amazing customer experiences. As an Expert, you introduce people 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
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.