Lesson 26: Troubleshoot Startup and System Issues

Question 1

What are the primary system initialization stages in macOS?

What are the visual and audible cues for these items?

Answer 1

Each primary stage of system initialization can be indicated by the following:

• Firmware, on most Mac computers you will hear a startup chime or bright flash of the power-on light followed by the monitor powering on
• Booter, an Apple logo on the primary display
• Kernel, a small progress bar below the Apple logo
• Launchd, later parts of the startup progress bar followed by the login screen

Question 2

What does the firmware do?

What is the POST?

Answer 2

The firmware initializes the Mac computer’s hardware and locates the booter file on a system volume.

The Power-On Self-Test (POST) checks for basic hardware functionality when your Mac powers on.

Question 3

What role does the launchd process play during system startup?

Answer 3

The launchd process is ultimately responsible for starting every process and application.

Thus, it manages system initialization and starts the loginwindow process.

Question 4

Which items are automatically started by launchd during the system initialization process?

Answer 4

During system initialization, the system launchd process automatically starts:
• /System/Library/LaunchDaemons
• /Library/LaunchDaemons, and the
• /etc/rc.local UNIX script (if it exists)

Question 5

What are the primary user session stages in macOS?

What are the visual and audible cues for these items?

Answer 5

Each primary stage of the user session can be indicated by the following:

• The loginwindow process displays the login screen
• The launchd process loads applications like the Finder after user authentication
• The user environment is active whenever the user is logged in to the system

Question 6

What is the difference between launch daemons, launch agents, and login items?

Answer 6

Launch daemons can open at any time (including system initialization) via the launchd process on behalf of the root user.

Launch agents and login items open also via the launchd process, but only after the initialization of the user environment.

Question 7

What are Safe Sleep and Power Nap?

Answer 7

Safe Sleep is a feature of all portable Mac computers that saves the system’s state to permanent storage in cases where the Mac computer’s battery drains completely.

Power Nap is a feature of Mac systems introduced after mid-2011. Power Nap allows the Mac to automatically wake in a low-power mode so that the system can perform a variety of application and system updates.

Question 8

What happens during user logout?

Answer 8

During user logout, the user’s loginwindow process does the following:

• Requests that all user applications quit
• Automatically quits any user background processes
• Runs any log-out scripts
• Records the logout to the main system.log file
• Resets device permissions and preferences to their defaults
• Quits the user’s loginwindow and launchd processes.

Question 9

What happens during system shutdown?

Answer 9

At system shutdown, the loginwindow process logs all users out and then tells the kernel to quit all remaining system processes.

Once the kernel quits all system processes, the Mac shuts down.

Question 10

Which keyboard shortcut is used to start up macOS in safe mode?

Answer 10

To start up macOS in safe mode, you hold down the Shift key during system startup.

Question 11

Which keyboard shortcut can be used to temporarily choose another startup disk?

Answer 11

Holding the Option key at startup opens Startup Manager, which allows you to temporarily choose another startup disk.

Question 12

Which changes are made when macOS starts up in safe mode?

Answer 12

When macOS starts up in safe mode, it performs the following permanent actions:
• Attempting to repair the system volume structure
• Deleting system KEXT caches
• Deleting font caches

Question 13

Which items are not loaded when macOS starts up in safe mode?

Answer 13

When macOS starts up in safe mode, it does not load:
• Third-party KEXTs
• Third-party launch agents
• Third-party launch daemons
• Third-party startup items
• Third-party fonts
• Any user login items
• Any user-specific launch agents

Question 14

How do you further resolve an issue that disappears when the Mac successfully starts up in safe mode?

Answer 14

If an issue disappears when the Mac successfully starts up in safe mode, you must find and remove the third-party startup resource that caused the issue.

The best way to isolate the problematic item is to start up the Mac in verbose mode and then observe where the startup process fails.

Verbose mode is initiated by holding down Command-V during system startup.