Download OS X Mountain Lion: Startup Process

OS X Mountain Lion: Startup Process
Introduction
This lesson covers the startup process for OS X Mountain Lion. Each stage in the process will be reviewed in detail, which will help you troubleshoot
and resolve startup issues.
OS X Mountain Lion: Startup Process is a component of the Apple Certified Mac Technicians (ACMT) certification and recertification training
curriculum.
Lesson Overview
Lesson Objectives
Explain the OS X startup process and its different stages.
Recognize when the startup process if abnormal.
Identify potential startup issues and associated fixes.
Demonstrate when and how a Safe Boot is used.
Determine and resolve common startup issues.
Audience
Prerequisites
Time Required
Technicians studying for ACMT
certification or recertification.
OS X Mountain Lion: Installation
30 Minutes
The Startup Process
The startup process begins when the power button is pressed and ends when the desktop appears. The entire process is comprised of these three
stages:
1. Hardware
First, the system powers up, tests and prepares the hardware.
2. Firmware
The computer's firmware (permanent software embedded in hardware) is loaded.
3. Software
The boot loader (program that places the operating system into memory) is loaded. The operating system loads and starts everything else
required by the login stage. Most startup issues occur at this stage. The selected user logs in (either automatically or using the login window) and
the operating system sets up the user's environment.
Stage 1: Hardware
1. Power On and Self Test
When you press the power button, the Mac provides power to the logic board and performs a quick check of the hardware. This hardware check is
called the power-on self test (POST). This test resides in read-only memory (ROM) of the computer.
If the POST is successful, the Mac will emit a startup chime. If a fault is detected, it will emit error tones instead. When this occurs, the screen
remains black.
What do the error tones mean?
Tone(s)
1 tone, a 5-second pause,
repeat
3 successive tones, a 5-second
pause, 3 successive tones
Description
No RAM installed
RAM does not pass data integrity check
1 long tone when holding down
Firmware upgrade in process. See About firmware updates for
the power button
Intel-based Macs for more details.
3 long tones, 3 short tones, 3
Firmware restoration from CD in process. See About the Firmware
long tones
Restoration CD (Intel-based Macs) for more details.
Stage 2: Firmware
2. Firmware Loads
The computer's firmware (permanent software embedded in hardware) is loaded. While it loads, the Mac displays a blank gray screen. The
firmware decides which startup disk to use (hard disk, Recovery HD, Internet Recovery, installation disc or NetBoot server).
If FileVault or firmware password is enabled, the Mac will require that the correct password be entered to continue.
Startup Disk Issues
When a Mac displays this flashing folder at startup, it is unable to find a startup disk that contains boot files.
When a Mac displays this prohibitory sign at startup, the Mac is not compatible with the installed version of OS X.
Stage 3: Software
3. Boot Loader is Loaded
When the gray Apple is displayed, the boot loader has been successfully loaded from the startup disk. The Boot Loader is a specific file called
"boot.efi" (found in the /System/Library/CoreServices/ folder).
4. Kernel Loads Files
While the kernel and related files load, it also checks the directory and starts services (like virtual memory and other launch agents). During this
process, a spinning gear is displayed under the Apple.
5. Graphical User Interface Starts
When the gray screen is replaced with the dark linen background, the OS X Mountain Lion graphical user interface (GUI) processes have started.
6. Login Window or Desktop Appears
Finally, you can log in. Based on your preferences, OS X Mountain Lion will prompt you for a name and password or automatically log in bringing
you directly to the desktop.
7. User Environment is Prepared
The Finder opens and OS X Mountain Lion looks for user accounts, user-owned files and starts running processes. This includes the Finder and
Dock.
8. Login Items are Loaded
OS X Mountain Lion then opens login items (as set in the Users & Groups System Preference pane).
What is a Safe Boot?
Safe Boot is a special way to start up when troubleshooting. After a Safe Boot, the Mac will enter into Safe Mode, which will assist in isolating and
identifying problems.
To perform a Safe Boot, hold the Shift key as the Mac starts up. The Safe Boot startup screen appears:
What does Safe Boot do?
It forces a directory check of the startup volume
It loads only required kernel extensions (some of the items in /System/Library/Extensions)
It disables all fonts other than those in /System/Library/Fonts
It disables all startup items and login items
Deletes the dynamic loader shared cache at (/var/db/dyld/). A cache with issues may cause a blue screen on startup, particularly
after a Software Update. Restarting normally recreates this cache.
The behavior of some devices (such as an AirPort card or USB peripherals) may also vary in Safe Mode.
These changes can help resolve software or directory issues that may exist on the startup volume.
Important
1. Safe Boot may take longer than normal. When you see the progress indicator (spinning gear), the disk's directory is being
checked and or repaired. This process may take several minutes.
2. You cannot perform a Safe Boot if the computer owner or administrator has enabled firmware password protection.
3. If FileVault is enabled, the correct password must be entered.
Symptoms & Fixes
Hardware Stage: Power-on self test (POST) Fails
Symptom
You hear no chime, hear a series of error beeps, or see a flashing LED on the computer after you press the power button.
Resolution
Before proceeding, consult hardware-specific resources to match specific LED codes or error beeps to specific symptoms.
1. Remove any third-party or other added hardware (including RAM), internal or external devices, and try again.
2. Reset the computer's PMU, SMU, or SMC to resolve power issues.
3. Reset NVRAM:
a. Shut down the computer.
b. Locate the following keys on the keyboard: Command, Option, P, and R.
c. Turn on the computer.
d. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
e. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
f. Release the keys.
4. Run Apple Hardware Test, if possible, to identify common hardware failures.
5. Perform any other appropriate hardware troubleshooting or repairs.
Hardware Stage: Mac displays blank gray screen or question mark
Symptom
Upon startup, Mac fails to progress past blank gray screen or displays a folder with a question mark:
Resolution
This condition tells us that the firmware has not found the boot loader on a startup disk. If this screen displays for more than a minute:
1. Reset NVRAM:
a. Shut down the computer.
b. Locate the following keys on the keyboard: Command, Option, P, and R.
c. Turn on the computer.
d. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
e. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
f. Release the keys.
If the issue persists:
2. Try starting from the recovery partition.
If you can start from the recovery partition, but resetting NVRAM fails to resolve the blank gray screen:
3. Reinstall OS X Mountain Lion.
When a Mac displays a folder with a question mark, it has searched all available devices, and is unable to find a startup disk that
contains boot files.
Startup Stage: Mac doesn't progress past spinning gear
Symptom
Mac displays the gray screen with the Apple logo, shows a spinning gear, never progresses past it or shuts down.
Resolution
This symptom signals that the kernel cannot completely load the operating system.
1. Continue to wait.
The system can perform a disk directory check automatically if it was shut down improperly. This process may take longer on larger hard disks.
If you determined that the startup has truly failed:
2. Start up the computer from the recovery partition.
Hold down "Command" and "R" keys at start up.
3. Run Disk Utility to repair the startup disk.
This can fix directory issues that can undermine the System Folder.
If the issue persists:
4. Reset NVRAM to clear any boot settings that may cause this issue.
a. Shut down the computer.
b. Locate the following keys on the keyboard: Command, Option, P, and R.
c. Turn on the computer.
d. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
e. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
f. Release the keys.
If the kernel could not progress and displays the prohibitory sign below, this indicates that the root device or startup disk driver
could not be found, disk verification failed, or the computer is not compatible with this version of the Mac OS.
Startup Stage: Startup process stops at dark linen background
Symptom
The startup process stops at the dark linen background.
Resolution
When this occurs, OS X Mountain Lion failed to load its graphical environment and system services.
1. Start up into Safe Mode to see whether corrupt fonts or extensions are causing the issue.
Hold down the shift key during start up.
2. Check the logs in Console (system.log or Console messages) for failure errors around the time of the last boot attempt.
If you cannot isolate the cause:
3. Boot from the recovery partition.
Hold down "Command" and "R" keys at start up.
4. Use Disk Utility to repair the startup volume's directory and/or permissions.
If Disk Utility reports no errors and you have repaired the volume's directory and/or permissions:
5. Reinstall OS X Mountain Lion.
Console is a utility built in to OS X Mountain Lion that displays log files. You can check the Console if you can start from the hard
drive in Safe Mode, or check other log files using Terminal while started from the installation disc.
Startup Stage: Login window doesn't appear
Symptom
Mac is set to log in automatically, but does not.
Resolution
1. Go to System Preferences > Users & Groups.
2. Select Login Options.
3. Verify that Automatic login is turned on.
If you restart and the login window still doesn't appear:
4. Start up from recovery partition.
Hold down "Command" and "R" keys at start up.
5. Use Disk Utility to repair the startup volume's directory.
If this doesn't remedy the problem:
6. Reinstall OS X Mountain Lion.
Login Stage: User environment doesn't appear
Symptom
After manual or automatic login, the Finder doesn't appear.
Resolution
The contents of the user's home directory may be the cause.
1. Log in as another user, if possible.
2. If the Dock or status menus aren't visible, try starting some applications.
If the issue is not isolated:
3. Start up from recovery partition.
Hold down "Command" and "R" keys at start up.
4. Run Disk Utility, and repair the startup disk.
If the problem is still not resolved:
5. Start from another volume.
6. Examine console logs on the problematic volume
(system.log and any crash logs)
If the problem still exists:
7. Reinstall OS X Mountain Lion.
Login Stage: Before completely starting up, Mac stops responding
Symptom
User can log in, but OS X Mountain Lion stops responding before the Mac has completely started up.
Resolution
Try suppressing login items.
1. Start up into Safe Mode to see whether login items are causing the issue.
Hold down the shift key during start up.
If you are able to login:
2. Go to System Preferences > User & Groups.
3. Click Login Items for the affected user.
4. Try deleting login items.
Restart and verify the fix. If this doesn't isolate the problem:
5. Reinstall OS X Mountain Lion.
Troubleshooting Practice
Scenario
Since Amy updated software on her iMac, it displays a blue screen on startup.
What built-in startup mode might help her resolve and troubleshoot this issue?
Click to reveal answer.
Perform a Safe Boot. Hold the Shift key as the Mac starts up.
One of the actions of Safe Boot is to delete the dynamic loader's shared cache. A cache with issues may cause a blue screen on startup, particularly
after a Software Update. Restarting normally recreates this cache.
Learning Resources
About firmware updates for Intel-based Macs
Intel-based Mac: Startup sequence and error codes, symbols
OS X Mountain Lion: If “You need to restart your computer” appears
OS X Mountain Lion: If you see a gray screen at startup
OS X Mountain Lion: Start up in safe mode
Startup Manager: How to select a startup volume
Starting from an external USB storage device (Intel-based Macs)
Startup key combinations for Intel-based Macs