Editor’s Note: The following article is an excerpt from Ted Landau’s Take Control of iPhone OS 3, a $15 electronic book available for 30 percent off specially for Macworld readers (dropping the price to $10.50). The 202-page ebook from TidBits Publishing helps readers understand what’s going on under the hood of the iPhone, with lots of tips for using the iPhone more effectively and an emphasis on troubleshooting assistance for solving problems related to syncing, application crashes, iPhone freezes, and more.
During a sync, iTunes not only syncs managed information and media, but also creates or updates an iPhone backup. The main function of the backup is to permit you to restore personal data and settings to your iPhone during a Restore (during which the content on the iPhone is typically erased). It also provides a good way to transfer data from an old iPhone to a new one.
Here’s a quick list of what exactly is stored in an iPhone Backup:
- Various settings from the Settings app data, including Mail and Calendar account settings (but not the actual Mail messages and Calendar events).
- Paired Bluetooth devices.
- Safari bookmarks and Safari AutoFill data.
- SMS and MMS messages, Notes items, voice memos, and photos and video from the Camera Roll. The one exception is that videos greater than 2 GB are not backed up.
- Preferences and data for third-party apps (such as game high scores), but not the apps themselves.
- Passwords for Mail and Wi-Fi accounts (from the iPhone’s Keychain file). These passwords will restore only to the same iPhone. If you upgrade to a new device, for example, you must re-enter these passwords on the new device. You may also have to reset your Voicemail password.
A backup does not store photos synced via iTunes nor any iPod music or video. For a complete list of what does and doesn't get backed up, see this Apple support document on iPhone and iPod touch backups.
Create or update a backup
When you connect an iPhone to iTunes and initiate a sync, a backup is the first step that occurs during the sync. A new backup is created automatically if one does not already exist. Otherwise, the sync updates an existing backup.
Because a backup is the first step in a sync, events later in the sync sequence (such as new apps being installed) have no effect on the backup. Such updating occurs at the next backup. (A backup will typically not recur during a subsequent sync if the iPhone has remained connected to iTunes. To force a new backup, disconnect and reconnect the iPhone.)
Alternatively, you can force a backup at any time without doing a sync. To do so, Control-click (right-click) your iPhone in the Devices section of the iTunes sidebar. From the contextual menu that appears, choose Back Up.
Note: The contextual menu that contains the Back Up command also contains a Restore from Backup command. This command allows you to restore backed up data to your iPhone without having to do the complete erasure required when doing a full restore, which we’ll cover below.
Speed up backups: Regardless of how you initiate a backup, it can take a significant amount of time (although the speed is greatly improved in iPhone 3 compared to earlier versions of the iPhone OS). One way to reduce the time is to delete unwanted photos and videos from the Camera Roll.
View backup lists, items, and data
To see a list of your current backups, go to the Devices pane of the iTunes Preferences dialog. If you sync more than one iPhone or iPod touch to your Mac, there will be a separate backup for each device.
The actual backup files are stored on your Mac in
~/Library/Application Support/MobileSync/Backup. Within this folder are more folders, each one named with a long string of hex characters (numbers from 0-9 and letters from a-f). Inside these folders are the actual backup files.
You can’t directly view any of the data stored within a Backup using iTunes or any other Apple-provided utility. However, you can gain limited access to some of the data (such as SMS/MMS messages and call history) via third-party utilities such as the MobileSyncBrowser (donationware). Your iPhone need not be connected to your Mac to view the backup data via these utilities.
To be truly amazed at all that can potentially be extracted from the backup files, including virtually every image stored in every temporary cache on the drive, try the $18 File Juicer.
New in iPhone 3 (for the iPhone 3GS) is an option, in the iPhone’s Summary tab in iTunes, to Encrypt iPhone Backup. This option encrypts the backup data and adds password protection. If it is enabled, you must enter the password to restore from a backup. This encryption also prevents anyone from viewing the Backup data using the aforementioned third-party software. However, it has no effect on similar software that can view contents by reading data directly from the iPhone itself (such as PhoneView; $19.95).
Time-stamped backups: Backup items marked with a date and time stamp are created after a Restore. They may also occur after a backup without syncing. These time-stamped backups are not overwritten by newer backups, leaving you with multiple backups for a given device. In general, once you have a more current backup and you are confident that you no longer need to restore again from the older backup, you can delete the older time-stamped one.
Delete a backup
To delete a backup, open the Devices pane in the iTunes Preferences dialog, select the backup, and click the Delete Backup button. Why would you want to do this?
• Old backups: There may be more than one backup listed for the same iPhone. If so, unless you have some reason to want to save older data, you can safely delete older Backups, maintaining just the most recent one.
• Corrupted backups: A corrupted backup could cause a sync to fail. You can fix the problem by deleting the suspected backup and syncing again—ideally, quitting iTunes and relaunching it before syncing. A fresh backup, presumably not corrupted, is created during the next sync.
As an extra precaution, you can Option-drag the folder for the to-be-deleted backup file from the Backup folder to the Desktop before deleting it (if you have more than one backup folder, the one you want to delete is most likely the one with the most recent modification date). This makes a copy of the backup. If it turns out that deleting the backup has no beneficial effect, you can return the copy to the backup folder and thus avoid losing the data unnecessarily.
• Selling a phone or switching computers: You might also want to remove a backup if you sell or otherwise part with your iPhone, especially if you are not getting a replacement iPhone, or if you intend to sync your iPhone to another computer.
Restoring your iPhone
When you restore your iPhone, you access the backup file on your Mac to restore your customized settings and related data to the iPhone. Normally, you would do this if you are having problems for which other techniques (such as the reset options in the Settings > General > Reset on the iPhone) are unable to fix.
You can restore in two different ways:
- A backup-only restore copies data from your iPhone’s backup file to the iPhone. It does nothing else.
- A full restore similarly restores data from your iPhone’s backup, but it also replaces (and updates, if needed) the iPhone’s operating system. A full restore, unlike a backup-only restore, erases your iPhone first.
For most troubleshooting, you’ll want to do a full restore. A full restore is also useful for transferring all your data from a currentÑperhaps defective, but still functionalÑiPhone to a replacement iPhone. After a full restore, you'll need to do a sync to put back all the media content on your iPhone.
When would you use a backup-only restore? If, for example, some data has been lost, corrupted, or deleted in error, a backup-only restore would let you recover that data (unless the data was added since the most-recent backup) without the hassle of having to erase the iPhone.
Make a backup of the backup: It’s always wise to have a backup of your iPhone backup, such as a copy stored via Time Machine. If the backup listed in iTunes fails or is incomplete, you can instead attempt to use your Time Machine backup copy.
Before you restore
Before you begin a restore, consider the following:
Download photos: Photos in the iPhone’s Camera Roll should be automatically saved to the iPhone’s backup file when you sync. However, to be sure that these photos are not lost during a restore, and to make sure you have saved the most recently added photos, separately download them to your computer first. You can do this via applications such as Image Capture or iPhoto.
Sync first or not:
- For a backup-only restore, you probably don’t want to sync your data prior to the restore. The point of a backup-only restore is to replace the current data with the backed-up data. If you sync first, you may accidentally replace the backed-up (good) data with newer (bad) data.
- For a full restore, unless you are concerned about transferring corrupted data from your iPhone to your computer, you should sync your iPhone first. This ensures that you back up the latest data prior to the restore.
To do a backup-only restore:
- Connect your iPhone to your computer, launch iTunes, and select the iPhone in the sidebar.
- Control-click (or right-click) your iPhone in the sidebar, and choose Restore from Backup.
- You will get a dialog requesting that you select which backup file to use, (assuming you have more than one). You’ll typically want to select the most current backup for the connected device.
To do a full restore:
- Connect your iPhone to your computer, launch iTunes, and select the iPhone in the sidebar.
- Make sure you have an active Internet connection.
- In the iPhone’s Summary tab (pictured to the right), click Restore.
- Follow the prompts that appear. The contents of your iPhone are completely erased. Next, if needed, the latest version of the iPhone software is downloaded. After the download is complete, the original factory settings for the iPhone are restored and your phone is re-activated by your cellular provider.
- When your Mac says that the iPhone needs to restart, click OK. A screen eventually appears, noting that “An iPhone has been previously synced with this computer.”
- Select “Restore from the backup of…,” choose the desired backup to use for the restore (assuming you have more than one), and click Continue. The iPhone accesses the backup on your computer and uses it to restore your iPhone settings and related data. This can take several minutes.
- Click Sync to return all your previously synced content (music, videos, photos, calendar items, and contacts) to the iPhone. This can take a half-hour or more, depending upon how much content you have.
- Confirm that the update installed the latest version of the iPhone software: in iTunes, click the Check for Update button in the iPhone’s Summary tab.
- If you use a passcode lock on your iPhone, you must reset it, since the restore deleted it (see Use Passcode Lock, ahead).
Your iPhone should now be nearly completely restored to its pre-erased condition. A few items may be missing in action; for instance, after a restore, I’ve lost custom stocks I’ve added to the Stocks app, and account passwords in Mail. But your troubles should (hopefully) be gone.
Full restore without updating
Normally, when you do a full restore of your iPhone, the process installs the latest version of the iPhone software (either from your drive or after downloading a newer version if needed). However, if you are not currently running the latest version and wish to keep things that way, you can typically do so. That is, you can reinstall the same version of the iPhone OS you are currently running rather than downloading and updating to the newer version. This could be desirable, for example, if you know that updating will break some third-party app that you want to use.
To restore without updating, hold down the Option key when clicking the Restore button in iTunes. This brings up an Open dialog. From here, navigate to
~/Library/iTunes/iPhone Software Updates. This is where the iPhone Restore files are located. For example, for iPhone OS 3.1.2 on an iPhone 3GS, the file is named
iPhone2,1_3.1.2_7D11_Restore.ipsw. Select the desired Restore file. With iPhone OS 3.1 or later, you’ll likely find only the most-recently added update file here.
With the latest iPhone models, you may not be able to reinstall your current version after a newer version is out. This is because iTunes checks Apple’s servers, over the Internet, prior to restoring and may permit only the latest version to be installed on these iPhones. Still, it’s at least worth a try. No matter what model you have, you cannot use this procedure to downgrade from the current installed version to an older version of the software.
Note: There is a separate iPod Software Updates folder for iPod touch updates. Ideally, don’t mix and match; especially avoid using an iPhone update file to update an iPod touch.
[Ted Landau is the guru of Macintosh troubleshooting, thanks to best-selling books and innumerable magazine articles for Macworld and many other publications. His latest book is Take Control of iPhone OS 3 (TidBits Publishing, 2009). You can reach him on Twitter at @tedlandau.]
This story, "Understand the iPhone backup" was originally published by Book Excerpt.