Mac OSX Operating System Security

Time Machine: Automatic Backups for your Mac

What is Time Machine?

Time Machine is automatic backup software that comes with Mac OS X. It allows you to backup your entire Mac, including system files, applications, accounts, preferences, email messages, music, photos, movies, and documents to an external drive. After the initial backup is complete, Time Machine will continue to perform hourly backups on any files that have been changed since the last time it ran. When your external drive is filled, Time Machine will start to delete the oldest existing backups in order to free up space.

Configuring Time Machine with an External Drive

Start by connecting an external drive to your Mac’s USB, FireWire or Thunderbolt ports.

Important: Time Machine only works with external drives that are formatted in Mac OS Extended (Journaled), Mac OS Extended (Case sensitive, Journaled) and XSan formats. Time Machine does not work with drives formatted for Microsoft Windows (NTFS or FAT formats). If you try to use a drive formatted for Windows, Time Machine will prompt you to reformat your drive. WarningBefore you reformat your drive make sure that you no longer need the files stored on it, as reformatting will erase all the data on the drive.

If you have never specified a Time Machine Backup device, Time Machine will display a dialog similar to this one:

Clicking “Use as Backup Disk” will confirm that you want to use the drive for Time Machine Backups, and will open Time Machine preferences with your drive selected as the backup destination.

Note: The option to Encrypt your Backup drive is available in Mac OS X 10.7 (Lion) and later. Checking this option will encrypt your External drive using FileVault 2.

Time Machine preferences will look similar to this:

Time Machine menu

You can check the status of your backup by clicking on the Time Machine icon in the menu bar:

time machine menu

Selecting Items to Exclude from the Backup

If you have files that are both large and frequently modified, it is helpful to add them to exclude them from the backup in order to save space. This is because Time Machine backs up any files that have been modified since the time of the last backup. So, if you have a 1 GB file that is changed frequently, the entire 1 GB will get backed up every time Time Machine runs which can use up a lot of space on your drive.

In order to add things to the exclude list, open Time Machine preferences and click the option button. A window similar to this will appear:

From this window you can choose to exclude files, folders or entire volumes from the backup. In order to add something to the excluded items list, simply click the plus sign button and chose the file, folder or volume you do not want to backup.

Restoring Specific Files or Folders

Open the Time Machine menu and select “Enter Time Machine”. This will open the restore interface as seen below.

You can view each backup by the time it was created using the timeline on the right side of the screen.

  • If you want to restore a specific file or folder, you can search for it using Spotlight, and then click the forward and back arrows in the bottom right corner of the screen in order to scroll through each backup that contains the specified item.
  • You can preview a file to see if it is the one you want by highlighting the file and then pressing the space bar.
  • To restore a file or folder, select the item you want to restore, and it will be copied to its appropriate folder.

Restoring your Entire Mac Using Time Machine

Time Machine can be used to completely restore your machine to the state it was in at the time of a backup. This feature should be used if your computer is unable to boot, or if changes have been made to your computer that you are unable to fix. Most commonly it is used for a computer that has either a corrupt operating system, or some sort of malicious software or virus.

Restoring a backup to the Mac that it was created on

Restart your Mac and hold down the Command and R keys at startup. This will cause your computer to boot from the Recovery System instead of Mac OS. In the Recovery menu that appears there is an option to restore from a Time Machine backup.

Migrating a backup to a new Mac

Time Machine can also be used to transfer files, applications and settings from a backup to a new Mac. To do this, connect your drive containing Time Machine backups to the new Mac. If this is your first time using the new Mac, the Setup Assistant will run, and ask if you would like to restore from a backup. If you have already run Setup, then use Migration Assistant to transfer data from the backup.


This blog post was written using information and pictures found in Apple’s Time Machine documentation.