How To Set Up and Monitor Time Machine

This Tech Tip covers provides you with instructions on how to set up and monitor Time Machine. It also explains some basic concepts behind Time Machine’s operation. Monitoring your backup system is incredibly important to do. A backup system that isn’t working is useless. Do not simply trust or believe that your backup system is working. Check on it regularly. It’s even better to restore a file or two as a test to know that your data can be retrieved.

Time Machine is Apple’s backup application which comes bundled with Mac OS X. It was introduced in 2007 as part of Mac OS X 10.5, Leopard. I have other Tech Tips that talk about swapping between two hard drives when using Time Machinerestoring a file from Time Machine and troubleshooting Time Machine if it’s not working.

Set Up

Time Machine is the easiest backup application to set up. For many users it can be as easy as connecting a brand new external USB hard drive to your Mac and turning it on. When you turn on the hard drive it will mount (appear) on the Desktop. Time Machine will detect this hard drive and present an on-screen message asking if you would like to use this hard drive for storing Time Machine backups, click the “Use as backup disk” button and you’re done.

While it can be this easy, there can be complicating factors, including these:

If Time Machine has previously been configured to use some other hard drive then you’ll need to manually configure it to use this new hard drive. To accomplish this, go to the Apple menu, select System Preferences and click on Time Machine, then click the “Select Disk” button. Select the new hard drive from the list. If you are using macOS 13 Ventura, go to the Apple Menu, select System Settings, click on General, then click on Time Machine and click the “Select Disk” button.

If the new hard drive is formatted as a PC hard drive using FAT32 or NTFS formats then Time Machine will prompt you to re-format the hard drive. [Important Note: Reformatting a hard drive entails erasing everything that is currently on the hard drive. So, review the contents of your external drive to make sure everything can be deleted before your reformat it.] I tend to buy my hard drives from Other World Computing or some other vendor that offers 3 year warranties on hard drives. I figure that a longer warranty indicates that better quality components were used in the drive and 3 years is typically the longest warranty that I see for non-server-class hard drives.

Initial Backup

Once Time Machine is configured to use a particular hard drive, backups will automatically occur every hour as long as the Mac is on and awake and the selected hard drive is available. The first backup will start within two minutes of you selecting it. The first backup can take many hours, but you can continue to use the computer while the backup is running. I typically start the initial Time Machine backup near the end of the day. This way it can run all night, as needed.

Which files are backed up?

Time Machine backs up nearly all files on your Mac. It backups all of your data files (music, email, bookmarks, photos, etc) as well as applications (Word, Safari, iTunes, etc) and Mac OS X itself. It’s useful to know that it does not backup files in the Trash. It also does not backup most cache files, log files and the iPod photo cache. You also have the ability to manually exclude a file or folder by going back to System Preferences and clicking on Time Machine, then clicking the “Options” button and adding an item to the list.

Backup Retention

After the initial backup is complete, subsequent backups only add new and/or modified files. Subsequent backups run automatically every hour, however not every backup is kept for ever. If every hourly backup was kept forever your backup hard drive would fill up very quickly. Instead, Time Machine automatically does some pruning of old backup files. Hourly backups are kept for the past 24 hours. Beyond 24 hours, the last of those 24 backups are kept and the other 23 are pruned or deleted. After one month, one backup is retained for each week and the other daily backups are pruned. Once the backup hard drive becomes full, Time Machine will notify you that it needs to delete the oldest backups in order to make room for the newest backups. I typically recommend using a backup hard drive which has at least twice the amount of storage space as you have files. For example, my laptop has about 150 GB of stuff on it. Thus, I should use a backup drive that is at least 300 GB in storage capacity.

Day-to-Day Monitoring

After you’ve set up Time Machine, the next most important task you can do is monitor Time Machine to ensure that it’s operating properly. A backup system that isn’t working is useless. To monitor Time Machine simply click on the Time Machine icon located in the upper right corner of your screen near the clock. The Time Machine icon looks like an arrow curving around in a circle with clock hands inside the circle. Click on this icon and read the first line. It should read  “Latest Backup: Today 2:15 pm” or something similar. If your most recent backup was not today then you should select “Back Up Now” from the Time Machine menu. You can then click on the Time Machine icon to monitor the status of the backup. Commonly seen messages are Preparing, Backing up X Megabytes of XYZ Megabytes, and Cleaning Up.

If your Time Machine backup system is not working properly, the most common cause is that your backup hard drive has become disconnected or is turned off. Do you see your backup drive’s icon on the Desktop? If not, check for loose cables and to make sure that it’s turned on. Also, disconnect and then reconnect the cable which connects the hard drive to your Mac.  If you’re still not able to get the backup drive to show up then restart your Mac. Afterwards, manually start Time Machine to see if it works now. If it’s still not working, you could refer to either of the web sites I list below or contact your Mac support person for assistance. (For an expanded version of these instructions check out my article about troubleshooting Time Machine.)


It’s best to know how to restore a file from your Time Machine backup before a crisis hits. Thus, you should practice performing a restore in order to get comfortable with the procedure. This way you can remain calm should a crisis arise. I’ve written a separate Tech Tip about how to restore files from Time Machine.

Apple’s introduction to setting up, restoring from and troubleshooting Time Machine.

Mr. Pondini has created a very thorough web site about Time Machine, including extensive Frequently Asked Questions and Troubleshooting sections.

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