by Tom Nelson
The Mac, and for that matter most computing platforms, are just chock full of daemons. Daemons, not to be confused with demons, are usually small programs that run in the background with no direct interaction with the computer user. They are often used to implement or help provide a service that operating systems or applications need.
The word daemon comes from an ancient Greek belief, and is used to describe a supernatural being that works on tasks between the gods and man. If we replace man with computer user, and gods with the operating system or applications, we get a reasonable idea of what all these Mac daemons are doing: performing repetitive tasks that provide a service to the operating system, an app, or the user.
Activity Monitor and Daemons
Daemons have no visible interface; they run in the background and are usually independent of other apps and programs. That makes them hard for the user to directly interact with, or even know they’re present. But without them, your Mac would likely grind to a halt or freeze up, possibly without even displaying the usual spinning beach ball of doom.
For the most part, daemons should be left alone; they’re perfectly happy performing their assigned tasks. But if you’re curious, you can use Activity Monitor, an app included with the Mac, to see how the various daemons, and other programs that are running, are making use of your Mac’s resources.
In this example, we’re going to use Activity Monitor to look at what two common Mac daemons are up to: “cfprefsd” and “cloudd.” We chose these two daemons because there have been a few questions floating around the Internet about what they do, as well as questions about these daemons using excessive resources.
You may notice that our two daemons have names that end with a “d.” This is a developer convention, where all daemons’ names should end with a “d.” Just as important, the rest of the daemon name should loosely describe its function. If we apply this developer logic to our two example daemons we come up with:
cfprefsd: A background process (a daemon because of the d at the end of the name) having something to do with cfprefs. Scratching our heads a bit, we can guess that this daemon has something to do with preferences, and if we knew a bit more about Mac development, we could guess the cf stood for Core Foundation.
Using the “man” command in Terminal allows you to see a description of what the daemon’s function is. [Press the “q” key to quit from the man page.] Screen shot © Coyote Moon, Inc.
Actually, we cheated a bit and used the Terminal app to tell us what cfprefsd was. You can use this trick with most of the daemons that are spawned by the operating system to discover what function they serve.
Launch Terminal, located at /Applications/Utilities, and enter the following at the Terminal prompt:
man cfprefsd
Terminal will tell us that, “cfprefsd provides preference services for the CFPreferences and NSUserDefaults APIs.” If we wanted to find out more, we could look up CFPreferences and NSUserDefaults in Apple Developer documentation. Essentially, cfprefsd helps an app or the system to read or write to preference files. When you open an app and change one of its preferences, it’s likely that cfprefsd is the daemon being asked to make the changes to the app’s preference file.
cloudd: A daemon having something to do with macOS cloud services. A little more investigating using Terminal and the technique we outlined above tells us that this is the daemon used by CloudKit, a developer’s API used to transfer data between an app and Apple’s iCloud service.
To check on this daemon’s activity, launch Activity Monitor, located at /Applications/Utilities.
When the Activity Monitor window opens, we’re going to be interested in the resources each daemon is making use of.
In the Activity Monitor window, select the CPU button in the toolbar.
You’ll see a long list of processes running on your Mac. You may notice a few daemons, processes whose names end with d, present in the list. But you probably won’t see cfprefsd or cloudd unless you scroll around a bit to find them. An easy way to see each daemon is to enter one of their names in the Search field in the top right corner of the Activity Monitor window.
For this example, enter cfprefsd in the search field.
Activity Monitor will list any matching process names that are running. You may see multiple daemons with the same name, indicating that multiple users (system, user, or other apps and processes) are making use of the daemon. In my case, I have three copies of the cfprefsd daemon running; one that my logged-in user is using, one the root user is using, and one that locationd (another daemon) is using.
Use the Activity Monitor search field to isolate the daemon you are looking for. Screen shot © Coyote Moon, Inc.
The most important columns in Activity Monitor to examine are the %CPU and Threads columns. In this example, there is 0 CPU being used by any of the cfprefsd daemons, and only two threads in use.
If the %CPU or Threads count were high, and stayed high for a long period, that could indicate a problem with the daemon, or more likely, the app or process that is using it.
Select the Memory button in the Activity Monitor window.
Daemons generally do not use a great deal of memory for long periods of time. They can certainly need memory resources while actively performing their tasks, but usually for short durations. If you see a large amount of memory in use by a daemon, and it stays that way for a long period of time, you may have an issue with the app or process that is using the daemon.
Clear Activity Monitor’s search field to see the full list of active processes. Or, you can enter the name cloudd to view the resources being used to support iCloud.
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