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

Duplicate Annihilator 5.8.3 - Find and d...
Duplicate Annihilator takes on the time-consuming task of comparing the images in your iPhoto library using effective algorithms to make sure that no duplicate escapes. Duplicate Annihilator detects... Read more
MarsEdit 3.7.10 - Quick and convenient b...
MarsEdit is a blog editor for OS X that makes editing your blog like writing email, with spell-checking, drafts, multiple windows, and even AppleScript support. It works with with most blog services... Read more
WALTR 2 2.0.9 - $39.95
WALTR 2 helps you wirelessly drag-and-drop any music, ringtones, videos, PDF, and ePub files onto your iPhone, iPad, or iPod without iTunes. It is the second major version of Softorino's critically-... Read more
Paperless 2.3.9 - $49.95
Paperless is a digital documents manager. Remember when everyone talked about how we would soon be a paperless society? Now it seems like we use paper more than ever. Let's face it - we need and we... Read more
Adobe After Effects CC 2017 14.1 - Creat...
After Effects CC 2017 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous After Effects customer). The new, more connected After Effects CC... Read more
Adobe Premiere Pro CC 2017 11.0.2 - Digi...
Premiere Pro CC 2017 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Premiere Pro customer). Adobe Premiere Pro CC 2017 lets you edit... Read more
ExpanDrive 5.4.4 - 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
Apple Final Cut Pro X 10.3.1 - Professio...
Apple Final Cut Pro X is a professional video editing solution.Completely redesigned from the ground up, Final Cut Pro adds extraordinary speed, quality, and flexibility to every part of the post-... Read more
Apple GarageBand 10.1.5 - Complete recor...
The new GarageBand is a whole music creation studio right inside your Mac -- complete with keyboard, synths, orchestral and percussion instruments, presets for guitar and voice, an entirely... Read more
Yummy FTP Pro 1.11.14 - $29.99
Yummy FTP Pro is an advanced Mac file transfer app which provides a full-featured professional toolkit combined with blazing speeds and impeccable reliability, so whether you want to transfer a few... Read more

Super Mario Run dashes onto Android in M...
Super Mario Run was one of the biggest mobile launches in 2016 before it was met with a lukewarm response by many. While the game itself plays a treat, it's pretty hard to swallow the steep price for the full game. With that said, Android users... | Read more »
WarFriends Beginner's Guide: How to...
Chillingo's new game, WarFriends, is finally available world wide, and so far it's a refreshing change from common mobile game trends. The game's a mix of tower defense, third person shooter, and collectible card game. There's a lot to unpack here... | Read more »
Super Gridland (Entertainment)
Super Gridland 1.0 Device: iOS Universal Category: Entertainment Price: $1.99, Version: 1.0 (iTunes) Description: Match. Build. Survive. "exquisitely tuned" - Rock Paper Shotgun No in-app purches, and no ads! | Read more »
Red's Kingdom (Games)
Red's Kingdom 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Mad King Mac has kidnapped your father and stolen your golden nut! Solve puzzles and battle goons as you explore and battle your... | Read more »
Turbo League Guide: How to tame the cont...
| Read more »
Fire Emblem: Heroes coming to Google Pla...
Nintendo gave us our first look at Fire Emblem: Heroes, the upcoming mobile Fire Emblem game the company hinted at last year. Revealed at the Fire Emblem Direct event held today, the game will condense the series' tactical RPG combat into bite-... | Read more »
ReSlice (Music)
ReSlice 1.0 Device: iOS Universal Category: Music Price: $9.99, Version: 1.0 (iTunes) Description: Audio Slice Machine Slice your audio samples with ReSlice and create flexible musical atoms which can be triggered by MIDI notes or... | Read more »
Stickman Surfer rides in with the tide t...
Stickson is back and this time he's taken up yet another extreme sport - surfing. Stickman Surfer is out this Thursday on both iOS and Android, so if you've been following the other Stickman adventures, you might be interested in picking this one... | Read more »
Z-Exemplar (Games)
Z-Exemplar 1.4 Device: iOS Universal Category: Games Price: $3.99, Version: 1.4 (iTunes) Description: | Read more »
5 dastardly difficult roguelikes like th...
Edmund McMillen's popular roguelike creation The Binding of Isaac: Rebirth has finally crawled onto mobile devices. It's a grotesque dual-stick shooter that tosses you into an endless, procedurally generated basement as you, the pitiable Isaac,... | Read more »

Price Scanner via MacPrices.net

Apple Ranked ‘Most Intimate Brand’
The top ranked ‘”intimate” brands continued to outperform the S&P and Fortune 500 indices in revenue and profit over the past 10 years, according to MBLM’s Brand Intimacy 2017 Report, the largest... Read more
B-Eng introduces SSD Health Check for Mac OS
Fehraltorf, Switzerland based independant Swiss company- B-Eng has announced the release and immediate availability of SSD Health Check 1.0, the company’s new hard drive utility for Mac OS X. As the... Read more
Apple’s Education discount saves up to $300 o...
Purchase a new Mac or iPad using Apple’s Education Store and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free: -... Read more
4-core 3.7GHz Mac Pro on sale for $2290, save...
Guitar Center has the 3.7GHz 4-core Mac Pro (MD253LL/A) on sale for $2289.97 including free shipping or free local store pickup (if available). Their price is a $710 savings over standard MSRP for... Read more
128GB Apple iPad Air 2, refurbished, availabl...
Apple has Certified Refurbished 128GB iPad Air 2s WiFis available for $419 including free shipping. That’s an $80 savings over standard MSRP for this model. A standard Apple one-year warranty is... Read more
13-inch 2.7GHz Retina MacBook Pro on sale for...
B&H Photo has the 2015 13″ 2.7GHz/128GB Retina Apple MacBook Pro on sale for $100 off MSRP. Shipping is free, and B&H charges NY tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro (MF839LL/A): $... Read more
Laptop Market – Flight To Quality? – The ‘Boo...
Preliminary quarterly PC shipments data released by Gartner Inc. last week reveal an interesting disparity between sales performance of major name PC vendors as opposed to that of less well-known... Read more
IBM and Bell Transform Canadian Enterprise Mo...
IBM and Bell Canada have announced they are joining forces to offer IBM MobileFirst for iOS market-ready enterprise applications for iPad, iPhone or Apple Watch. Bell, Canada’s largest communications... Read more
Otter Products is Closing… For a Day of Givin...
On Thursday, Feb. 9, Otter Products is closing doors to open hearts. In partnership with the OtterCares Foundation, the company is pausing operations for a day so all employees can volunteer with... Read more
15-inch 2.2GHz Retina MacBook Pro on sale for...
Amazon has 2015 15″ 2.2GHz Retina MacBook Pros (MJLQ2LL/A) available for $1799.99 including free shipping. Apple charges $1999 for this model, so Amazon’s price is represents a $200 savings. Read more

Jobs Board

Senior Workstation Administrator - *Apple*...
…with extraordinary HR. QualificationsJOB SUMMARY/OVERVIEWThe Senior Workstation Administrator - Apple supports the mission of TriNet by providing advanced level Read more
Intermediate *Apple* macOS Systems Integrat...
**Position Summary:** SC3 is actively seeking an Intermediate Apple macOS systems integration administrator that will be responsible for providing Apple Mac Read more
*Apple* & PC Desktop Support Technician...
Apple & PC Desktop Support Technician job in Los Angeles, CA Introduction: We have immediate job openings for several Desktop Support Technicians with one of our Read more
*Apple* Retail - Multiple Positions - Apple,...
SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (Multi-L...
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.