This is a post that was recovered from another, very short-lived blog. Since the original seems to have vanished into thin air, I thought I’d repost it here, since it’s still relevant, and links to another article in this blog. Also, it seems that readers like this type of article — whenever I look at my blog stats, articles like this always tend to be among the top posts.
Lingon is one of those tools that at first blush may seem to be something only a true geek would love, but it’s actually fairly practical. What it does is to allow you to launch scripts or programs according to certain criteria. If you have previous experience with Linux or Unix, you can think of it as a way to set up something similar to a cron job, except that you have more flexibility.
One thing you can do is set up scripts or applications to launch at startup. Now, you may already know how you can launch applications at startup — you go into System Preferences, click on Accounts, and then (while your account is selected) click on Login Items. Once there, you can add or remove applications you want to launch at startup by using the + and/or – buttons. And, that’s the preferred way to launch an application at startup for the logged-in user.
But what if you want to launch an application based on some other criteria, or you want to launch a script of some kind? What if you need an application to start no matter which user is logging in? Or, what if you want to tweak an existing startup item that’s run by the system (as an agent or a daemon) and not by a particular user? That’s where Lingon comes in. Lingon lets you edit and create conﬁguration ﬁles for launchd (and maybe you are asking, what is launchd? Well, according to Wikipedia, “launchd is a unified, open source service management framework for starting, stopping and managing daemons, programs and scripts.” Aren’t you sorry you asked?).
To give you an example of how Lingon can be used, we set it up to start the CallerIDpop perl script from the Michigan Telephone, VoIP and Broadband blog. This is a script used with Linksys/Sipura VoIP adapters (and some phones) that, when there is an incoming call, provides a Growl popup showing caller details and the time the call was received (it can also write this information to a log file). Previously we had been using their suggested method of running an AppleScript (saved as an application) at startup, the AppleScript containing the line that actually starts the Perl script. Although this works, it’s a fairly convoluted way to do it and it seems to eat up a lot of system resources. So, we set out to find another way to invoke the script at startup. Here’s how we did it using Lingon (which, by the way, seems to get the script running a lot quicker, and the script itself seems to be running in a more stable environment):
When you first fire up Lingon, you get this screen:
Click the small button labeled “New” (with the + on the button) in the upper left-hand corner, and you get a dropdown as shown here:
We selected “My Agents” because we only have one user account on that system, and didn’t really want the script to have root privileges. You should think long and hard about running anything as a daemon, because if anything goes wrong (whether due to programming error or malicious intent) the script will be running as root and can do just about anything to your system. Having selected that, we got this window:
As you can see, everything is fairly straightforward. In section 1 you give the agent a name, in section 2 you insert the command just as you would enter it if you ran it directly from a terminal window (or you choose the application to run, if you are running an application), and in section 3 you pick the options you want to use to trigger running the script or application. If you’re not sure about any of the options, click on Help (in the top menu bar) and then “Lingon Help” and it will bring up a PDF file in Preview that explains how to use Lingon. The Help menu also gives you access to the man pages for launchd.plist, launchctl, and launchd, in case you are making changes in any of those files.
Note the “Expert Mode” button in the lower right-hand corner – this shows you the actual XML code, and allows you to write keys and values directly if you are comfortable doing that.
Don’t forget to click the “Save” button at the top when you are finished – we forgot to do that and had to start all over! We sort of wish that the “Save” button were underneath the other three sections, maybe in a section 4!
Unfortunately, to make everything work properly you’ll have to log out and login again, or reboot your Mac, as Lingon will remind you:
Not only can Lingon be used to make your own script or application launchers, but it can also be used to edit existing system agents and daemons. While you normally shouldn’t do this, if you know what you are doing it can sometimes improve system performance. On the other hand, if you don’t know what you are doing, you could render your system totally inoperable! As an example of why you might want to do this, we recommend you see the article, “The Case of the Slow Mac (and how to fix it)” at Maciverse. If you think that your Mac is running a bit sluggish, or if you’re seeing the “spinning beachball of death” a bit too often, this article explains one possible reason, and a suggested fix that’s much easier to make if you use Lingon.