Advanced Mac users often make changes to the OS via Terminal commands. For some of the simpler options, there are apps available that allow novice users (ones who don’t venture to Terminal) to make these same changes through a graphical UI. For advanced users though, the Terminal really is one of the preferred places to go when a system tweak is to be applied. AppKiller is a free Mac app that has been designed for both novice and advanced users. The name is slightly misleading though, since it doesn’t just kill apps, but also system processes, and provides an easy way to quit/restart the Finder, AirPrintDaemons, AirPort Utility etc. AppKiller executes commands in one of two ways; either by a click, or via Control + Click symbol. For each executable function, you can set one default action from the app’s preferences. It includes a number of BSD signals that you can send to an active app or process. The app’s response will of course depend on how it’s written and how it treats the BSD signal.
AppKiller runs in the menu bar, and at the time of installation, it requires administrative privileges i.e. you will need to enter your user account password once when you install the app. Clicking the icon reveals an entire list of every single process that is currently running, If you were to open the Activity Monitor, you would see the same process running. Apps like Chrome will appear more than once since each tab is treated as a separate instance.
In order to sort how the process are listed, open the Preferences menu and sort your items by PID (Process ID), CPU or Memory Usage. You can choose to view additional information i.e., User ID, Process ID and User Name, for each process in the menu. At the very bottom, you will find two options including Click Sends and Control+Click sends. For each option, another menu opens with a list of commands that will be sent to the process you select. Listed commands include Quit, Interrupt, Terminated, Suspended CPUtime limit exceeded, Signal 0, EMT Trap and more. Only one option can be picked from this list as the default one, but it can be changed any time.
Remember that not all processes will react the same way, and the app behavior depends on their nature and how a command is executed for each one. Take for example the Kill command. If you Kill Notification Center, its icon will disappear from the Menu Bar and you will have to launch it again to get it back. Conversely, if you were to Kill Dock, it would restart again automatically since it has to keep running.
As stated earlier, AppKiller also has the ability to send BSD signals to running user processes as well as system processes. This feature may help users resolve app or process specific issues. For instance, if an app consumes too much system resources, you can choose to send Segmentation fault signal to the app or its related processes in order to fix the issue. Similarly, you can send illegal instruction signal to an app or process that is not programmed for your system’s CPU or when the app is trying to execute privileged or garbage instructions.
A while back we covered another slightly similar app called Crtl+Alt+Delete that allows you to simply quit apps (including ones running in the background). AppKiller is not an app that you should use unless you know what it does and you have a good understanding of what BSD signals are. If you just need a simple app quitting utility, try the Ctrl+Alt+Delete app instead. AppKiller is best suited for power users who often need to execute one of the available commands and would like shortcuts for frequently used commands.