Troubleshooting OS X Start-ups
Your Mac was running fine. It started up quickly, it was zippy when you worked and snappy when you played. But suddenly something's wrong: when you start it up, it takes longer-maybe a couple of minutes, maybe more-than it once did. What's slowing things down?
There can be a lot of reasons your Mac is taking longer to start up. Here are the troubleshooting steps you should take, in order, to find out what's wrong and fix it.
The first thing to check is the hardware devices connected to your Mac. Sure, they might have been working just fine before the slowdowns started; unfortunately, electronic devices can go bad.
First, disconnect every external hardware device but your mouse and keyboard: that includes hard drives, printers, scanners, extra input devices, hubs, network cables, and even cables that connect to your iPod. Restart your Mac.
Startup still slow? If you have a spare mouse and keyboard, disconnect your current input devices, connecting the spares, and restart. If the problem persists, and if you use wireless AirPort networking, select your Internet connection in the Network preference pane and make sure the correct DNS servers are listed in the DNS Server box; they should be the ones specified by your ISP.
Let's say you're lucky-one of these steps resolves the slow startup. You can then figure out which device is the problem by reconnecting your peripherals one at a time and restarting after each addition. If and when your startup chokes up, the last peripheral you added is the problem.
Alternatively, you could connect half of your peripherals and then restart. If that works out, connect the other half and restart. If the problem crops up in either case, split the offending subset in two and repeat until you narrow down to the culprit.
Assuming your peripherals aren't the problem, your next suspect is recently installed software.
Did you add any new programs lately? Did you update Mac OS X or any of its components such as QuickTime, Safari, or any other system update that required you to restart your Mac? Did you update any drivers (software that runs a device such as a printer or scanner)?
If the answer to any of the above questions is yes, the first thing to do, if possible, is uninstall the suspect software. For a recently added new application, you can try to remove it using either the uninstaller that came with the program or a utility such as the $13 AppZapper.
Removing updates to the operating system or its built-in apps (Safari et al) is trickier. If you have a recent backup of your system, such as a Time Machine backup, you could try restoring the entire system to the state it was in before you installed the suspect software. Don't just restore individual folders (such as System or Library); you need to restore the whole thing.
Again, go step-by-step: uninstall all your new software, then reboot your system. If startup goes faster, add the new software back one piece at a time, rebooting between each reinstall, until you identify the culprit. If removing all that software doesn't help, move on to the next step.
Note: If your Mac has been taking a long time to reboot since you installed a system update, the slowdown may be normal; several recent OS X updates have caused this problem, and you'll just have to wait for the fix from Apple.
It may be that neither your hardware nor your new software is causing the problem. In that case, your next suspect is software that is or isn't loading at startup.
To find out if login items are causing the problem, press and hold the shift key just after you enter your user name and password at the login screen; this temporarily disables login items. (If your Mac is set to log in automatically, press and hold the shift key as soon as the blue screen appears on your monitor.)
Choose an account in the left column to see all of its login items. Hover the cursor over an item, and a tooltip will appear, showing its path.
If disabling login items solves your slow startup problem, you need to identify which item is the cause. In the Accounts preference pane, click on the Login Items tab. Scan the list: do you see anything there that you don't recognize? Sometimes programs you no longer use leave items on this list. If you're sure you don't need an item, select it and click on the minus-sign (-) button to delete it. Then reboot and see if that helped.
Assuming the problem persists, next you should check the items that load at system startup (as opposed to your own individual login). Most such items are in the /Library/StartupItems folder. Apple discourages developers from installing items here, but some still do.
To determine whether any of these items is causing your slow startups, restart your Mac and hold down the shift key as soon as you hear the startup chime; this tells OS X to do a Safe Boot, which means it'll load only essential kernel extensions. If your Mac starts up quickly in Safe Mode, move the contents of the StartupItems folder to the desktop, then try restarting to see if that resolves the problem. Does startup still go quickly? Then you know something in that folder is causing the problem; add the items in it back one at a time until you replicate the slowdown. Caution: Do not move anything from the /System/Library/StartupItems folder; only Apple's software resides there.
Now that you've eliminated peripherals, software, and startup items, your next suspect is your startup disk. If you have multiple hard disks in your Mac, the problem could come from any one of them not mounting correctly.
To find out if this is the problem, open Disk Utility (in the /Applications/Utilities folder) and use it to check all of your hard disks: select a disk in the left column, click on the First Aid tab, then click on either Repair Disk (for a nonstartup disk) or Verify Disk (for a startup disk). Check your startup disk first.
Use Disk Utility to check your startup disk for problems. If it finds any, reboot using your OS X install disk and run Disk Utility from there.
If Disk Utility says the startup disk needs repairs, you will have to boot off your Mac OS X installation disk. From there, run Disc Utility from the Utilities menu. If Disk Utility finds errors on other disks, it may be able to repair them, but in some cases it cannot. In that instance, you should use a program like DiskWarrior, which can repair many disk problems Disk Utility can't handle.
If a hard drive isn't causing the problem, other built-in hardware could be.
To make sure your Mac's innards are healthy, from the Apple menu, choose About This Mac, then select More Info to open System Profiler. Click on Hardware in the Contents column and check the information shown there about your Mac's model, processor speed and quantity, and installed RAM.
If the amount of RAM isn't what it should be, some memory modules may be unseated. In that case, you'll need to open your Mac (if you can) and make sure your RAM chips are firmly ensconced in their slots. Alternatively, you could take it to a nearby Apple Store or another reputable repair shop.
It's more serious if System Profile reports the wrong number of processors. In that case, you'll definitely need to have your Mac checked out professionally.
Have you gotten this far without resolving the problem? It's time to start checking your Mac's logs. You can view them using the Console application, located in your Utilities folder.
In particular, look at all the log entries that occurred just after startup. Click on All Messages in the left column and scroll up until you find messages from localhost kernel at the time you restarted your Mac. Scan the log from this point on for any error messages suggesting that software did not load correctly because it couldn't be found. (Those messages shouldn't be too hard to spot; they'll say something like "could not load.")
If none of these suggestions solves your startup woes, search Apple's support site for "troubleshoot startup."
[Senior contributor Kirk McElhearn writes about more than just Macs on his blog Kirkville.]