Carbon Copy Cloner | Bombich Software

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By default, CCC will copy everything from the volume or folder that you specify as the source. If you do not want to copy every item from the source, you can define a task filter to limit what items will be copied. Choose Copy Some Files from the popup menu underneath the Source selector, then click on the Task Filter button to open the Task Filters panel.

Default Filter Behavior

The CCC task filter offers two paradigms for defining the task filter. The task filter can either include everything by default or the filter can exclude everything by default. Which behavior you choose depends on what you want CCC to do with new items that are added to the source.

Include everything by default: Define what is excluded

CCC's default behavior is to include everything by default. In this mode you define what is excluded from the backup task by unchecking the box next to an item in the file list. This mode is simplest for users that only want to exclude a handful of items, but generally back up everything because you don't have to revisit the task filter to indicate that new items should be included in the backup task. If you add a file or folder to the source (e.g. in the future after defining your task filter), and that item is not in a folder that you have excluded from the backup task, that item will automatically be included in the backup task.

Exclude everything by default: Define what is included

In this mode, everything is excluded by default, and you define what is included in the backup task by checking the box next to an item in the file list. If you add an item to the source in the future, and that item is not in a folder that is specifically included by the task filter, that item will not be backed up. This mode is helpful in cases where you only want to back up a handful of items on a volume whose subfolders frequently change.

Calculating disk usage and Protected Size

You can right-click on any folder and choose Refresh size to have CCC enumerate the contents of that folder and evaluate the task filter against its contents. CCC will report the total size of the folder and the protected size of the folder (i.e. how much data is included in the backup task). You can also click on the Refresh Disk Usage button to enumerate the contents of the entire source. This could take a while, especially for network volumes, so consider refreshing the disk usage of individual folders instead. If CCC is in the midst of enumerating a folder, you can right-click on that folder to stop enumeration, or click again on the Refresh Disk Usage button to stop the calculation.

Source and destination options

By default, CCC won't copy the contents of the Finder Trash because, well, it's Trash. If you want CCC to back up your Trash, uncheck the Don't copy Finder's Trash box to remove the exclusion.

Excluded files are not deleted from the destination

When you exclude an item from the CCC backup task, this tells CCC, "Do not copy that item". That does not, however, indicate that CCC should delete that item from the destination, e.g. if it had been copied there by a previous backup task. In fact, excluding an item from the backup task implicitly protects that item on the destination. If you have items on the destination that are now excluded from a backup task that you no longer want to retain on the destination, you can simply remove them from the destination by dragging them to the Trash. If you would like CCC to facilitate that cleanup, check the Remove excluded files checkbox.

This option is ignored if your task is configured with the Don't delete anything SafetyNet setting. This setting also will not override CCC's explicit protections placed on the _CCC SafetyNet folder, so when this option is used in conjunction with CCC's "SafetyNet On" setting, items will be moved to the SafetyNet folder rather than deleted immediately.

Please carefully consider the scope of effect that this option will have when using the Exclude everything by default filter behavior.

The Protect root level items setting is described in more detail in the Advanced Settings article.

Custom Filters

If the files you want to match are scattered across your filesystem, it may be tedious to manually locate each of them and create conventional rules (i.e. check or uncheck the item in the file list). To address this, CCC offers custom filter options in which you define a filter rule using an expression. Choose Show custom filters from the gear menu to reveal the custom filters table.

To add a custom filter rule, click the + button in the custom rules table header, or drag a file or folder from the file list into the custom filters table to add that item as a template. To reorder custom filters, simply drag and drop the items in the custom filters table. Custom filter rules will be evaluated by the task filter before conventional filter rules.

Anchored path filter

An anchored path filter defines a rule using an absolute path relative to the root of the source. /Library/Caches, for example, is an anchored path filter because it starts with a "/". This filter would match /Library/Caches, but would not match /Users/someuser/Library/Caches. You can also include wildcards in the expression, e.g. /Users/*/Library/Caches would match the Library/Caches folder in each user home folder.

Subpath filter

A subpath filter defines a rule using a partial path or filename that does not start with "/". Continuing the example above, Library/Caches would match /Library/Caches and /Users/someuser/Library/Caches. Wildcards are accepted in the expression; to match a particular file type, use an expression like *.mov to match all .mov files.

Wildcard characters

Wildcard characters can be added to an expression to match a wider range of files and folders. * will match one or more characters in any single file or folder name, e.g. *.mov will match all movie files.

/**/ will match one or more path components, e.g. /Users/**/*.jpg will match any JPEG photos in any user home folders, but won't match JPEG photos elsewhere, e.g. those in /Library/Desktop Pictures. You would also use the ** wildcard when defining an inclusion rule that should copy all items within a particular folder and its subfolders. For example, /Users/yourname/Documents would include only that folder itself, not any of its contents. /Users/yourname/Documents/** would include the Documents folder, all of its contents, and the contents of every subfolder within it.

If you specify additional path components after a ** wildcard, then that wildcard is only applicable up to a match against the path component that follows the wildcard. For example, the exclusion rule /Data/**/Marine/Invertebrates would exclude /Data/2018/Marine/Invertebrates, but it would not exclude /Data/2018/Marine/Benthic/Marine/Invertebrates. In the latter case, **/Marine matches 2018/Marine, but then the the next path component fails to match (and we are deliberately choosing to not allow the ** wildcard to match 2018/Marine/Benthic in this case).

? can be used to match any single character, e.g. *.mp? will match both .mp3 and .mp4 files. Use the ? wildcard sparingly, it will greatly increase the amount of time required to evaluate the task filter.

Expert settings

Custom filter rules are usually applied to include or exclude an item. Exclusions, however, are actually composed of two behaviors: a matching item on the source will not be copied (Hide the item from the copier), and a matching item on the destination will be protected (Protect the item from the copier). Likewise, Inclusions indicate that a matching item on the source will be copied (Show the item to the copier) and a matching item on the destination may be deleted (Risk the item). Occasionally it's helpful to define a rule that affects only matching items on the source or only on matching items on the destination. For example, if you have a folder named "Archives" on the destination that does not exist on the source, that item won't appear in the source list so it cannot be excluded (and thus protected) in the conventional manner. You could add an /ArchivesProtect rule to explicitly protect that item on the destination.

Including folders and their content with the 'Exclude everything by default' filter behavior and custom rules

Including a folder or a bundle file and its contents via a custom rule requires a non-intuitive expression, because the filter rule must match multiple path components. To include a folder and all of its contents, add ** to the end of the filter expression. For example, to include the Photos Library from your home directory, the following expression would apply as an inclusion rule:

/Users/johnny/Pictures.Photos Library.photolibrary**

Exporting and Importing filters

A whole task filter can be imported or exported via the gear menu. When importing a filter, the current filter will be replaced with the filter you're importing. CCC will automatically purge conventional rules from the filter if they are not applicable to the currently-selected source. For example, f you had excluded /Applications in the filter, but /Applications does not exist on the current source, that rule will be removed from the filter to avoid unexpected results should an /Applications folder ever be added to the source. This purging is not applicable to custom filter rules.

You can also export individual or groups of custom filter rules. Select the rule(s), then simply drag the items onto your Desktop. To import custom rules from a file exported in this manner, simply drag the file into the custom filter rules table.

Items automatically excluded

Carbon Copy Cloner excludes some items from the backup task by default. A complete list of exclusions along with an explanation for the exclusion is available in this section of the documentation. If you would like to visualize the items that are automatically excluded, hold down the Option key while clicking on the Task Filter button to open the Task Filters window.

The CCC SafetyNet folder, "_CCC SafetyNet" is excluded by a global filter. See the Frequently asked questions about the Carbon Copy Cloner SafetyNet section of the documentation to learn how to restore items from that folder.

Additionally, CCC will exclude and protect system folders if you select the startup disk or a non-HFS+/APFS formatted volume as the destination. If you would like to restore a specific item, such as the contents of /Library/Application Support, this protection can be avoided by choosing a specific folder at the source and destination via the Choose a folder options in the Source and Destination selectors. With great power comes great responsibility — take care to avoid overwriting your system files.

When do I need to create a Recovery HD volume?

CCC bootable backups offer similar functionality to the Recovery HD volume, so the Recovery HD volume is not strictly required on a backup volume. Unless you have a specific reason to not create a Recovery HD, though (e.g. because it could affect a Boot Camp partition on the same disk, you don't want to give up the 1GB, etc), we recommend that you maintain a Recovery HD volume on your backup disk. Especially if you intend to use your destination volume in production (e.g. you are migrating to a larger disk, or restoring to a replacement disk), or if you intend to enable encryption on the backup volume, then you should create a Recovery HD volume for the destination volume. If you intend to enable encryption on the destination volume, we recommend that you create the Recovery HD volume before enabling encryption. A Recovery HD volume is not required for restoring an installation of macOS from a CCC bootable backup.

What is the difference between archiving the Recovery HD and creating a new Recovery HD?

During the course of an ordinary backup of a volume that contains macOS, CCC will automatically create an archive of the Recovery HD associated with that volume. This archive is stored on the source volume, and is subsequently backed up to the backup volume along with everything else. This archive of the Recovery HD volume can be used in the future to create a new Recovery HD, and it's the first source that CCC considers when you choose to create a Recovery HD. The archive is not, however, an operational Recovery HD volume, it's just a backup file.

CCC's Disk Center offers the ability to create an operational Recovery HD volume as well. This functionality is completely separate from creating an archive of the Recovery HD. Unlike the archiving of the source Recovery HD, creating a new Recovery HD is not something that happens automatically, you have to ask CCC to do this in the Disk Center. When CCC creates a new Recovery HD, it borrows space from your destination volume to create a new, hidden volume on that disk. The resulting Recovery HD is fully operational — you can boot your Mac from it and reinstall macOS. Refer to the previous section to determine if creating a Recovery HD is required in your situation.

Why were other volumes on my disk unmounted when I created a Recovery HD?

CCC uses a command-line version of Disk Utility to resize the donor volume. Resizing that volume requires making changes to the partition table on the disk, and Disk Utility may choose to unmount other volumes on the disk while it makes those changes. CCC will specifically remount the donor volume, but whether Disk Utility remounts the other volumes is a function (or bug) of Disk Utility. You can remount these volumes manually in Disk Utility.

Can I create a Recovery HD on an Apple Fusion (aka "CoreStorage") volume?

No, not with CCC. Creating a Recovery HD requires borrowing space from a physical volume, and that is not a modification that we recommend making to an underlying member of an Apple Core Storage logical volume. The only Apple-supported method of creating a Fusion volume is via Disk Utility or the macOS Installer, and each of those will create a Recovery HD volume before the Fusion volume is created. If you intend to create your own Fusion volume using one of the various tutorials available on the Internet, and if you want that volume to have an associated Recovery HD volume, we strongly recommend that you create a Recovery HD volume before creating the Fusion volume. You can use CCC to create the Recovery HD volume on the slowest disk that you intend to add to the Fusion logical volume group. See the following document for a demonstration.

Creating a Fusion volume with a Recovery HD

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There are several factors that affect the performance of your backup tasks. Here we describe the most common conditions that affect backup performance, and offer some suggestions for mitigating the effects of those conditions.

Reduce the number of files considered for backup

CCC analyzes all of the files that are included in your backup set for consideration to be copied. If you have a particularly high number of files on your source volume, you may want to put some thought into how your files are organized. For example, if you have a large number of files that never change (perhaps some old, completed projects), you can collect these into a folder named "Archives", back it up once, then exclude it from future backups. CCC will not delete excluded items from your destination (unless you ask it to using Advanced Settings), so as long as you keep the original on your source volume, you will always have two copies of your archived content. Because these items are excluded from your daily backups, CCC will not spend time or RAM enumerating through those files for changes.

Hard drive performance and interface bandwidth

Performance will be worse for smaller hard drives (e.g. physically smaller, like those in laptops), for older hard drives, and for hard drives that are nearly full and thus more likely to be fragmented. You will also get longer copy times when you have lots of small files vs. a volume filled with just a few very large files. Finally, you will see better performance with faster/more efficient interfaces — Thunderbolt is faster than Firewire, Firewire 800 is faster than USB 2.0, etc.

When you consider purchasing an external hard drive for backup, we recommend enclosures that have multiple interfaces (e.g. Firewire and USB, or Thunderbolt and USB). Depending on how you use the Firewire or USB interfaces on your Mac, you may find that you get better performance or reliability when trying a different interface on your external backup disk. Additionally, if your source volume is nearly full, we recommend that you replace it with a larger hard drive to avoid the performance implications of filesystem fragmentation.

Filesystem performance and hardware type

It's important to choose the right filesystem for the hardware that you have. If you have an older, rotational HDD, you should format that device using the "Mac OS Extended, Journaled" (HFS+) format. APFS is the new, modern standard, but its performance on rotational devices is far inferior to HFS+. Apple still recommends HFS+ for rotational HDD devices, and that's our recommendation as well.

Spotlight Indexing

Anything that causes CCC to compete for bandwidth to your source or destination volume will increase the amount of time that it takes to back up your data. Spotlight indexing is one such process that CCC typically must compete with for disk bandwidth. As you copy new data to your destination volume, for example, Spotlight wants to read those "new" files so it can index their contents. Having a Spotlight index of your backup volume may be unnecessary as you probably want to search for files only on your source volume. To disable Spotlight indexing on a volume that is dedicated to backup, drag the icon of the destination volume into the "Privacy" tab of Spotlight Preference Pane in the System Preferences application. If you do want the backup volume indexed, drag its icon out of the "Privacy" tab after the cloning and indexing will start immediately.

Find and replace corrupted files

CCC offers an advanced option to "Find and replace corrupted files". When using this option, CCC will re-read every file on the source and every file on the destination, calculating a checksum of each file. CCC then compares these checksums to see if a file should be recopied. While this is an excellent method for finding unreadable files on the source or destination, it will dramatically increase the amount of time that your backup task takes, and it will also increase CPU and hard drive bandwidth consumption on your Mac. We recommend limiting the use of this option to weekly or monthly, and scheduling such tasks to run when you are not typically using your Mac.

Other applications and conditions that can lead to performance problems

Over the years we have received numerous queries about poorer performance than what is expected. Careful analysis of the system log and Activity Monitor will usually reveal the culprit. Here are some things that we usually look for:

Other backup software copying simultaneously to the same volume, a different volume on the same disk, or across the same interface as CCC's destination.
Utilities that watch filesystem activity and do things when file changes are detected. Antivirus software is a common culprit, but we have also seen problems caused by other watcher applications, such as memeod and Western Digital's SmartWare.
Slow interfaces — USB hubs (including the ports on a USB keyboard or display) and even some USB cables can reduce the bandwidth to your disk dramatically. If you're using USB, be sure that your device is plugged directly into one of the USB ports on your Mac.
Daisy chaining Firewire devices is usually OK, though some enclosures can stall the entire Firewire bus when given too much bandwidth. If you see this behavior, try switching the order of devices in the chain, or attach your backup disk directly to a Firewire port on your Mac.
Using a wireless network connection to connect to a network volume. If you're seeing poor performance with a wireless connection, compare the performance when using a wired (ethernet) connection.

Use the Console application to view the contents of the system log. If you're still having trouble identifying a performance problem, we're here to help.

CCC will only back up system files to locally-attached macOS-formatted filesystems

macOS can only be installed on a macOS-formatted volume. This requirement is also carried to a backup volume. When system files are copied to non-macOS filesystems, important metadata are invariably lost, resulting in files that cannot be restored to their original functionality. In short, you cannot restore a functional installation of macOS from a backup stored on a non-macOS volume. To prevent any misunderstandings about this limitation, CCC will exclude system files from a backup task if the destination is not a locally-attached, macOS-formatted volume. Likewise, CCC will not copy system files from a network volume, e.g. if you were to mount the startup disk of another Mac, the system files on that network volume cannot be copied in a meaningful way.

Note that the "locally-attached" caveat is an important distinction. Even if your destination volume is macOS-formatted, if it is attached to an Airport Base Station (for example), then you're accessing the volume via file sharing. If you open the Get Info panel for the volume, you will see that the volume format is "AppleShare", not HFS+ or APFS. It is not possible to update an OS backup on a network volume. If you would like to maintain a backup of macOS on a network volume, you can back up to a disk image on the network volume. See the related documentation below for additional information on this backup strategy.

Ownership and permissions concerns

Network filesystems pose some interesting challenges in regards to preserving ownership and permissions. When you connect to another computer that is hosting a shared volume, you usually authenticate by providing a username and password. The account whose credentials you provide is an account on that other computer, and it is this account's privileges that determine what access you have to files and folders on the shared volume. Additionally, any files that are copied to the shared volume will be owned by that user account, regardless of the ownership of those files on the source volume. This is not a behavior specific to CCC, it is simply the nature of network filesystems.

An example will be very helpful in understanding the implications of this behavior. Suppose Sally would like to back up some Movies from her Mac's home folder to another Mac shared by Bob and Joe. On Sally's Mac, there is a user account named "sally". On Bob and Joe's Mac, File Sharing has been enabled in the Sharing Preference Pane, and there are two user accounts, "joe" and "bob". Bob has attached an external hard drive named "Backup" to his Mac that he and Joe have been using for backup, and he has created a folder named "Sally's Movies" on this volume to which Sally will copy files. Sally does the following to connect to Bob and Joe's Mac:

In the Finder, open a new window, then click on "Bob and Joe's Mac" in the Shared section of the sidebar.
Click on the Connect as... button.
In the authentication dialog, provide Bob's username and password, then click on the Connect button.
Choose the "Backup" volume from the list of shared volumes.

The Backup volume now appears on Sally's Desktop, and in CCC's Destination selector in the Network Volumes section. Next, Sally chooses Choose a folder... from CCC's Source selector and locates the folder of movies that she would like to copy to Bob and Joe's Mac. She then chooses Choose a folder... from the Destination selector and locates the "Sally's Movies" folder on the Backup network volume. She clicks the Clone button and the Movies are backed up.

Later that day, Joe is using his computer and he notices that he can see some of the movies in the "Sally's Movies" folder, but some of the subfolders have a universal "No access" badge and he cannot view those folders' contents. This occurred for two reasons:

Sally mounted the network volume using Bob's credentials, so the files and folders created when she copied her files to the Backup volume are now owned by Bob's user account.
Some of the folders on Sally's computer prevented access by "other" users.

As a result, the folders on the Backup volume are owned by Bob and some of them limit access to other users (Joe in this case). Joe asks Sally about this and she decides to try copying some of the movies to one of Joe's folders on the backup volume. When she chooses Choose a folder... from CCC's Destination menu, however, she sees the same universal "No Access" badge on Joe's folder. Sally can't copy files to this folder (nor can CCC) because the Backup volume was mounted using Bob's credentials, and Joe's backup folder on the backup volume happened to be inaccessible to Bob. Sally unmounts the backup volume and reconnects to it using Joe's credentials, and she is then able to copy files to Joe's private folder.

What can I do when there are permissions or ownership issues that prevent CCC from copying items to/from or updating items on a network volume?

First, it is important to keep in mind that no application can modify the ownership of a file or folder on a network share. Ownership changes must be applied on the computer or device that is hosting the network volume. Additionally, permissions changes can only be made to files and folders owned by the user whose credentials were used to mount the network volume. For this reason, it is generally easier to apply both ownership and permissions changes on the computer or device hosting the network volume.

If the computer hosting the network volume is a Mac, you can modify ownership and permissions in the Get Info panel for that folder (on the Mac hosting the network volume):

In the Finder, click on the folder whose permissions or ownership you would like to change.
Choose Get Info from the File menu.
In the Sharing & Permissions section at the bottom, click on the lock icon to make the permissions editable.
To change permissions, choose Read & Write from the popup menu next to the owner of the file or folder.
If the owner of the item is not the user account that you use to connect to this Macintosh, click on the + button
In the window that appears, select the user account that you use to connect to this Macintosh, then click the Select button.
Set the access privileges to Read & Write.
Click on the Gear menu and choose to apply the change to enclosed items.
Try your backup task again.

If the computer or device that is hosting the network volume is not a Macintosh, consult that device's documentation to learn how to change permissions and ownership of files and folders.

Alternative #1: If you have mounted the network volume with Guest privileges, unmount and remount the network volume using the credentials of an account on the machine or device hosting the network volume.

Alternative #2: You can create a new folder on the shared volume and specify that folder as the destination in CCC by choosing Choose a folder... from the Destination selector.

Alternative #3: You can have CCC create a disk image on the network volume rather than copying files directly to a folder. When CCC creates a disk image on the destination, the disk image is formatted as HFS+ and attached locally, so CCC can preserve the permissions and ownership of the files that you are copying to it.

Limitations of non-macOS-formatted filesystems

When you choose a non-macOS-formatted volume as a destination, CCC's Cloning Coach will proactively warn you of any compatibility issues between the source and destination volumes. You can view the Cloning Coach's warnings by clicking on the yellow caution button in the Task Plan header. If you have selected a source and destination volume, and the caution button is not present, then there are no configuration concerns.

Support for third-party filesystems

CCC offers limited support for third-party filesystems, such as those provided by FUSE for OS X. Due to the large number of filesystems that can be provided by FUSE, CCC provides generic support for these "userland" filesystems rather than specific support. CCC takes a best effort approach by determining the capabilities of the source and destination filesystems, warns of potential incompatibilities, then presents only unexpected error conditions that arise during a backup.

Backing up to FUSE volumes mounted without the allow_root flag is not currently supported (e.g. Google Drive, BitCasa). Please contact the vendor of your proprietary filesystem to ask that they offer the ability to mount the volume with the allow_root flag if you would like to use that volume as a source or destination to a CCC backup task.

Google Drive File Stream is a special case. We've seen odd behavior when selecting Google Drive File Stream volumes as a whole as the source or destination for a task – CCC is unable to read the root folder during a backup task. CCC explicitly disallows that configuration. Selecting a subfolder on the Google Drive volume does work, though, and CCC allows that configuration. There is one other notable concern with Google Drive File Stream – Google Drive will download files when they are accessed if they do not currently reside on your Mac's hard drive. If you specify a Google Drive folder as the source to a backup task, you should anticipate that cloud-only files may be downloaded to your Mac during the backup task. That behavior lies outside of CCC's purview, it cannot be modified with a CCC task setting.

The Western Digital MyCloud Home NAS device is another special case. The "Home" model of this NAS device requires the use of WD-proprietary software to access the storage securely; direct access to the storage via SMB is only available with Guest privileges. Users report that performance of the storage while using WD's software is subpar in comparison to Guest access via SMB, and other users have reported to us that macOS is unable to create or mount disk images on the storage when mounted via Western Digital's software. When you mount WD MyCloud Home NAS storage using WD's software, the volume is vended by a 'kddfuse' filesystem. CCC won't allow these volumes as a source or destination device. To back up to a WD MyCloud Home NAS, mount the storage via SMB in the Finder instead. Be sure to choose the "Guest" user option when prompted to authenticate, because the MyCloud Home device doesn't support authenticated access via SMB.

Writable NTFS filesystems

We have seen several reports of problems copying large amounts of data (e.g. > 4GB) to writable NTFS filesystems. In most cases, the underlying software that vends the filesystem (e.g. Tuxera, Paragon, and others) crashes and the volume is rendered "mute". While it may be possible to complete a backup to these filesystems in chunks (e.g. 4GB at a time), we recommend using a more reliable, writable filesystem if you encounter these problems.

Backing up a Boot Camp installation of Windows

CCC can back up the user data on a Boot Camp volume, but it cannot make an installation of Windows bootable. If your goal is to back up your user data on the Boot Camp volume, CCC will meet your needs. If you're looking to migrate your Boot Camp volume to a new hard drive, you might consider an alternative solution such as WinClone, or one of the commercial virtualization solutions that offer a migration strategy from Boot Camp.

Backing up the contents of an NTFS volume

The NTFS filesystem supports "named streams", a feature that is comparable to extended attributes on macOS-formatted volumes and many other filesystems. Unlike extended attributes, however, there is no limit to the amount of data that can be stuffed into NTFS named streams (aside from standard file size limitations). Extended attributes on macOS have a 128KB size limit. As a result, any attempts to copy a named stream larger than 128KB to a non-NTFS filesystem will fail. CCC will copy the standard file data just fine, but will not copy named streams larger than 128KB. CCC's Cloning Coach will warn of this kind of incompatibility, and any errors related to this limitation will be logged to the CCC log file, however these errors will not be raised to your attention.

This limitation applies when copying files between volumes on Windows as well, so application developers tend to use named streams only for data that can be regenerated (e.g. thumbnail icons, summary or statistical information), not for storage of irreplaceable user data.

NAS service failures can lead to unreliable backups

Access to the contents of a network volume is provided by an application that runs on another computer or Network Attached Storage (NAS) device. Every NAS device and operating system has its own vendor-specific version of the file sharing application, so we occasionally see problems with some NAS devices that don't occur on others. Problems can be minor, such as being unable to set file flags (e.g. hidden, locked) on an item, or more significant, like not being able to store or retrieve resource forks. When these problems are encountered during a backup task, CCC will copy as many files and as much data as possible, then offer a report on the items or attributes that could not be copied.

When you encounter an error caused by the file sharing service that hosts your network volume, there are a few workarounds that you can try to avoid the errors:

Eject the network volume on your Mac, then restart the computer or NAS device that is hosting the network volume. Reconnect to the network volume and try the backup task again.
Connect to the network volume using a different protocol. A different application is responsible for each protocol, so if the AFP service on your server has a bug, connecting to the SMB service may work more reliably (and vice versa). Choose Connect to server from the Finder's Go menu, then specify "smb://servername.local/volume " or "afp://servername.local/volume " to connect to the server using a different protocol. If you are unsure which protocol you are currently using, click on the mounted volume in the Finder, then choose Get Info from the Finder's File menu to find out.
If the errors persist when connecting to the network volume via both AFP and SMB, and restarting the file server does not change the outcome, try backing up to a disk image on the network volume instead.

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Often when you have a backup task that runs on a scheduled basis, there are associated tasks that you would like to perform before or after files are actually copied. CCC offers the option to run shell scripts before and after a backup task, unmount or set the destination as the startup disk, run another CCC backup task, and power management options such as restart and shutdown. If you would like to perform any of these pre or post clone tasks, click the Advanced Settings button below CCC's Source selector.

Mounting the source or destination volume before a backup task begins

Without any additional configuration, CCC will attempt to mount your source and destination volumes before a backup task begins. This applies to many different volume types — ordinary volumes on locally-attached hard drives, disk images, network volumes, encrypted volumes – even encrypted volumes on remote Macs. If your source or destination volume is on a disk that is physically attached to your Mac (e.g. via Firewire, Thunderbolt, or USB), but it is not mounted, CCC can "see" that device and will attempt to mount it. If your source or destination is a network volume, CCC will obtain the credentials that you use to mount that device when you create the backup task, and will use those credentials to mount the volume before the task begins.

This also applies for nested volumes. For example, suppose you are backing up to a disk image on a network volume. CCC will first attempt to mount the network volume, then it will attempt to mount the disk image. Likewise, suppose you have a task configured to back up the contents of a folder on an encrypted volume. If you have saved the encrypted volume's passphrase in CCC's keychain, CCC will unlock and mount the encrypted volume before the backup task begins.

CCC's attempts to mount the source and destination volumes occur automatically before any other tasks, including pre clone shell scripts (described below), therefore it is not necessary to implement a shell script to pre-mount the source or destination.

SafetyNet Pruning

SafetyNet pruning is covered in more detail in this section of CCC's documentation.

Destination volume options

If you would like CCC to unmount your destination volume at the end of the backup task, choose Unmount the destination volume from the Destination volume management menu. If your destination is a folder, the text will be Unmount the underlying volume. If the destination is a disk image, CCC always unmounts the disk image volume, so this setting refers to the underlying physical volume upon which the disk image resides.

CCC will not forcefully unmount the destination volume. If an application has open files on the destination volume, CCC's attempt to unmount the volume will fail. CCC does not report this as an error, though it will make a note of it in the Task History window.

Yosemite users have an option to set the destination volume as the startup disk. Starting in El Capitan, however, Apple's System Integrity Protection prevents third-party applications from changing the startup disk setting. We do not recommend disabling System Integrity Protection to make this feature work, rather we recommend that you use the Startup Disk Preference Pane to change the startup disk selection.

Power management options

By default, at the end of a backup task, CCC will not perform any power management tasks. Instead, the system will perform as defined by the settings in the Energy Saver preference pane. For example, if you have the system configured to idle sleep after 20 minutes, the system will go to sleep if there hasn't been any user activity in the last 20 minutes. CCC activity is not considered user activity, so often the system will go to sleep immediately after CCC finishes a backup task.

If you choose one of the options from the Power management menu, CCC will reboot or shut down your Mac when the backup task finishes. The reboot and shutdown options are not forceful. If you have a document open with unsaved modifications, for example, the application would prompt you to save the document. If a save dialog is not attended to, the shutdown or reboot request will time out.

Turn off the computer if it was previously off

If your backup task is scheduled to run on a regular basis, this option will be enabled in the Power Management popup menu. This option is applicable if you would like to have CCC shut down your Mac at the end of the task, but only in cases where the Mac was booted at the task's scheduled run time. If your backup task runs when the system has been on for a while or has been sleeping, CCC will not shut down the Mac when using this option.

Power Management options are ignored in some cases

Power management options will not be applied to backup tasks that are cancelled (e.g. you click the Stop button). Additionally, power management tasks will not be applied if other CCC backup tasks are running or queued to run immediately after the current task finishes running. If your task is running as part of a Task Group, power management options will be deferred to when all tasks within the group have completed.

Power Management options are applied regardless of task success

Power management options will be applied whether the backup task completes successfully or not. If you prefer for a backup task to perform the power management action only when the backup task exits without error, see the pm_on_success.sh postflight script below.

Run another backup task (task chaining)

If you have more than one CCC backup task configured, the other tasks will be listed in this popup menu. To create a task chain (e.g. to run tasks sequentially), simply choose one of these tasks to have that task run automatically after the current task finishes. Tasks run in this manner will start after the current task has finished completely. Chained tasks will run regardless of the exit status of a preceding task in the chain, e.g. if the first task reports errors or fails to run at all, the second task will still run.

Running shell scripts before and after the backup task

If there is functionality that you need that does not exist within CCC, pre and post clone shell scripts may be the solution for you. Pre clone shell scripts run after CCC has performed "sanity" checks (e.g. are the source and destination volumes present, is connectivity to a remote Macintosh established) but before copying files. Post-clone shell scripts run after CCC has finished copying files and performing its own internal cleanup, but before unmounting any volumes.

CCC passes several parameters to pre and post clone shell scripts. For example, the following shell script:

#!/bin/sh echo "Running $0" echo `date` echo "Source: $1" echo "Destination: $2" echo "Third argument: $3" # Exit status for post-clone scripts, underlying volume path for a disk image for pre-clone scripts echo "Fourth argument: $4" # Destination disk image path, if applicable

Would produce the following output (you can redirect this output to a file of your own specification) if implemented as a post clone script:

Running /Library/Application Support/com.bombich.ccc/Scripts/postaction.sh Wed Oct 8 21:55:28 EDT 2014 Source: / Destination: /Volumes/Offsite Backup Third argument: 0 Fourth argument:

First parameter

The path to the source volume or folder.

Second parameter

The path to the destination volume or folder. If the destination is a disk image, this is the path to the mounted disk image.

Third parameter

Pre clone script: The underlying mountpoint for the volume that holds the destination disk image, if applicable.
Post clone script: The exit status of the file copying phase of the backup task.

Fourth parameter

The path to the destination disk image, if applicable.

If your pre clone script exits with a non-zero exit status, it will cause CCC to abort the backup task. This can be used to your advantage if you want to apply preconditions to your backup operation. If you want to be certain that errors in your pre clone shell script never cause the backup task to be aborted, add "exit 0" to the end of your script. If you would like that script to silently cancel the backup task, add "exit 89" to the end of the script. If the script is a global preflight script (specified in the Advanced section of CCC's Preferences window), you can add "exit 104" to the end of the script to cancel the backup task and to avoid recording a Task History event.

The post clone script will run whether the backup task exits successfully or not. If your script should behave differently depending on the result of the task, you can test whether the third parameter is zero (an exit status of "0" means the task ended successfully). For example:

#!/bin/sh source="$1" dest="$2" exitStatus=$3 if [ "$exitStatus" = "0" ]; then # foo else # bar # Note: Do not assume that $source and $dest are populated # These will be empty if source or destination validation fails fi

If your postflight script exits with a non-zero exit status, CCC will not report this as a failure of the backup task. The failure will be noted in the Task History window, however.

AppleScripts are not supported

You cannot specify an AppleScript as a pre or post clone script, CCC currently only supports running shell scripts.

Shell scripts require a shell interpreter line

CCC does not assume a default shell environment when running your pre or postflight script. Not doing so gives users a great deal of flexibility; they can choose to write their scripts in any shell or programming language (e.g. bash, python, perl, ruby, C). For CCC to execute a shell script as an application, though, the system needs to know what shell should be used to interpret the script, and that value needs to be defined in your shell script. This is done simply by placing a shell interpreter line at the top of the file, e.g. #!/bin/sh.

Security implications of pre and post clone shell scripts

CCC's pre and post clone shell scripts are executed as the System Administrator. To prevent non-administrative users from making unauthorized modifications to your shell scripts, you should restrict which users have write access to these scripts and to the folder in which they are contained. The parent folder and scripts should be writable only by the owner (e.g. you). For example, running the following in the Terminal application would secure any shell scripts located in the default location for pre and post clone scripts:

chmod 755 /Library/Application\ Support/com.bombich.ccc/Scripts/*.sh

Example pre and post clone shell scripts

To use any of these example scripts, download the script and place it somewhere on your startup disk. By default, CCC looks in /Library/Application Support/com.bombich.ccc/Scripts.

parallels_pause.sh
This is a pre clone script that you can use to pause all currently-running Parallels VM containers. This script will also retain state information that can be read by the corresponding parallels_start.sh post clone script to resume these VMs after the backup task has completed. Note: This script relies on command-line tools offered only in Parallels Desktop for Mac Pro or Business Edition.

parallels_start.sh
This post clone script will resume any Parallels VM containers that were suspended by the parallels_pause.sh pre clone script. Note: This script relies on command-line tools offered only in Parallels Desktop for Mac Pro or Business Edition.

play_sound.sh
If you want to play a unique sound, use this script. You can plug in the path to any audio file of your liking or try one of the examples included.

eject_destination.sh
CCC's option to automatically unmount the destination volume is a volume-level task, not a device task. If you want to eject the destination device, use this post clone script instead. Note that ejecting the destination device will unmount all volumes on the device. Also note that this example script adds a 60-second delay to accommodate macOS's desire to automatically regenerate various cache files. This delay can be adjusted if necessary by editing the script.

rename_dmg.sh
This post clone script will rename the destination disk image, adding a timestamp to the disk image name. This is useful if you want to create snapshots of the source in disk image files for posterity. Note that this will cause CCC to create a new disk image during every backup task, and recopy everything from the source each time. Additional notes for configuring this post clone script are available in the script header.

pm_on_success.sh
This post clone script will perform the requested power management option (e.g. shutdown, restart, sleep) at the end of the backup task if the backup task completes without errors. Use this in lieu of one of the Power Management postflight options if you prefer the power management action does not occur when a task ends with errors (e.g. if the destination volume is missing).

quit_application.sh and open_application.sh
This pair of scripts can be used to quit and open an application before and after the backup task. Open these scripts in a text editor to define the application that should be quit or opened.

post_to_slack.sh
This postflight script will post the status of your backup task to a Slack channel.

ifttt_maker.sh
This postflight script will post an IFTTT Maker Event of the status of your backup task.

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Frequently Asked Questions (FAQ)

Advanced Topics

Note: The topics in this article are not relevant to APFS-formatted destination volumes that have CCC snapshot support enabled. For those volumes, CCC leverages snapshots to implement the SafetyNet functionality, and the snapshots aren't affected by any of the shortcomings described here.

How do I restore files from the _CCC SafetyNet folder?

CCC's SafetyNet folder ("_CCC SafetyNet") is excluded from CCC's backup tasks by default because it contains older versions of modified files, and files that were deleted from the source volume. Typically when you restore data from your backup volume, you will want to avoid restoring the items in this folder, choosing instead to restore the most recent backup of your files.

If there is something that you would like to restore from the CCC SafetyNet folder, a drag and drop restore in the Finder is usually the easiest way to do so. If you would like to restore many items, or merge them into an existing folder, choose Choose a folder... from CCC's Source selector and choose the folder from which you would like to restore. If you choose the _CCC SafetyNet folder as the source, note that the full path to your archived files will be preserved, e.g. 2017-07-27 (July 27) 14-11-18/Users/fred/Documents/some file.pdf. In most cases, you will want to choose a subfolder within the archives folder as your source. Likewise, choose Choose a folder... from CCC's Destination selector and select the specific folder that you want to restore items into.

Why can't I open some files in the _CCC SafetyNet folder?

When CCC evaluates the items on your destination and determines whether they should be archived or left in place, it does so on a file-by-file basis. This poses a challenge for bundle files — files that are actually a folder of files, but presented by the Finder as a single file. As a result, bundle files (e.g. applications, some types of libraries, some custom file types) may appear in an incomplete form within the CCC SafetyNet folder.

Unless all of the components within a bundle file are modified, only the items that have been updated will be present. Incomplete bundle files are generally not useful on their own, but their contents can be. For example, if you accidentally deleted a photo from your iPhoto library, you would be able to recover that lost photo from the archived iPhoto library bundle. To reveal the content of an incomplete bundle file in a CCC SafetyNet folder, right-click (or Control+click) on the item and choose Show package contents from the contextual menu.

Can I restore a previous version of the OS using one of the archives in the _CCC SafetyNet folder?

While it is possible to recover an older, complete version of a bundle file from the CCC SafetyNet folder and complete backup (e.g. by overlaying the incomplete archived bundle file on top of the current backup of the bundle file), this is generally too tedious of a task to be practical for application and OS restores. CCC's SafetyNet folder is not intended to offer a method for rolling back software updates, OS restores should always be done from the complete backup at the root level of your destination.

I deleted files from my startup disk to make more room, but now it's hard to find some of those files on my backup volume

This generally isn't a concern for ordinary "flat" file types, but it it can be a concern for certain applications that store lots of files in a single, monolithic-appearing container file. Some applications offer highly customized interfaces to access a specific file type. Photos, for example, allows you to manage tens of thousands of photo files. These files are all stored in a proprietary bundle file in your home folder, but because photos are so easy to organize within Photos, many people don't consider how those files are organized on the hard drive. Usually you really don't have to either. That is, of course, until you can no longer use Photos to access your photo files, and that's exactly what happens when you delete files from your Photos library, abandoning them to the SafetyNet folder on your backup volume.

If you have a habit of periodically deleting photos, music, or movies from Photos, iTunes, Aperture, or any other application that uses a proprietary bundle file format so that you can "free up some space on your startup disk", consider how those files will be organized on the destination. Specifically, keep in mind that you use a very elaborate application to access these files on the source volume, but you will only have the Finder to access these files on the backup volume.

CCC can't reorganize your deleted files in a way that's logical to you, it can only place them at the same path in the _CCC SafetyNet folder as they were on the source volume. For files buried in a bundle file on the source (as is the case for Photos, for example), this means that the files will be buried in bundle files in various time-stamped archive folders on the destination. These files will also be subject to deletion if you configure CCC to periodically prune the contents of the SafetyNet. In short, simply archiving deleted files from applications such as these isn't going to be the best way to store these items long-term if your goal is ultimately to keep them.

When you want to free up some space on your startup disk, consider this approach instead, using Photos as an example:

Create a new folder at the root level of your backup volume, named something like "Archived Photos 2016".
In Photos, delete all of the photos that you want to remove from your source volume. When you delete these items, they are placed in the Recently Deleted album.
Click on the Recently Deleted album in the Photos sidebar and select all of the photos in that folder.
Drag all of the selected photos from the Recently Deleted album to the "Archived Photos 2016" folder on the backup volume.
Once the photos are safely copied to and neatly organized on the backup volume (and ideally, after you have made a second backup of these precious files on some other volume), go ahead and click the Delete All button in the Recently Deleted album.

Not all applications have this kind of internal Trash folder, so be sure to see how it works for other applications before applying these exact steps. The general idea, though, is that you should deliberately archive the items that you're removing from your source volume in a way that makes sense to you rather than passively allowing CCC to archive them in a manner that makes sense to the computer.

Why can't I delete some items from the SafetyNet folder? The Finder says that some items are in use.

In OS X El Capitan, Apple introduced a new feature called System Integrity Protection (SIP). SIP works by preventing any user from deleting certain protected system items on the startup disk. If you boot your Mac from a backup volume and restore system files to your startup disk, CCC will place outdated versions of those system files into the SafetyNet folder. These modifications are allowed because CCC is making changes to that volume while it is not the current startup disk. When you restart your computer from that destination volume, however, SIP re-engages and may then prevent you from deleting the protected items that were placed into the SafetyNet folder. If you attempt to delete these items, the Finder will report that they cannot be deleted because they are in use, or because they are protected. If you try to delete these items in the Terminal application, you'll get a more distinct error message, "Operation not permitted".

CCC won't have any trouble pruning the SafetyNet folder on its own during ordinary backup tasks. If you would like to remove an item from the SafetyNet manually, however, or if you would like to remove the entire folder:

Choose Delete a SafetyNet folder from CCC's Utilities menu
Drag the folder you want to delete onto the window that is presented. Alternatively, you can click on the drop zone in the window that is presented to make your selection from a navigation panel.

If the item you're trying to remove is on your current startup disk, CCC will move the item to the root of your startup disk, then instruct you to boot your Mac from some other volume (e.g. your backup disk). Once booted from the backup volume, you can repeat the same steps with CCC to remove the SafetyNet folder.

If you're still having trouble after trying that, don't hesitate to ask us for help.

How can I prevent Migration Assistant from copying the CCC SafetyNet folder during a migration?

If your backup volume has a "_CCC SafetyNet" folder, you can move that folder to the Trash before using Migration Assistant to avoid copying that folder during a migration. This is particularly important if that folder has a lot of data in it and you're migrating to a disk that is smaller than the backup volume. If you would like to retain the SafetyNet folder on the backup volume, don't empty the Trash. After Migration Assistant has completed, then you can move the SafetyNet folder back to the root of the backup volume.

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Advanced Topics

Default Filter Behavior

Include everything by default: Define what is excluded

Exclude everything by default: Define what is included

Calculating disk usage and Protected Size

Source and destination options

By default, CCC won't copy the contents of the Finder Trash because, well, it's Trash. If you want CCC to back up your Trash, uncheck the Don't copy Finder's Trash box to remove the exclusion.

Excluded files are not deleted from the destination

Please carefully consider the scope of effect that this option will have when using the Exclude everything by default filter behavior.

The Protect root level items setting is described in more detail in the Advanced Settings article.

Custom Filters

Anchored path filter

Subpath filter

Wildcard characters

Expert settings

Including folders and their content with the 'Exclude everything by default' filter behavior and custom rules

/Users/johnny/Pictures.Photos Library.photolibrary**

Exporting and Importing filters

Items automatically excluded

Reduce the number of files considered for backup

Hard drive performance and interface bandwidth

Performance will be worse for smaller rotational hard drives (e.g. physically smaller, like those in 2.5" hard drive enclosures), for older hard drives, and for hard drives that are nearly full and thus more likely to be fragmented. You will also get longer copy times when you have lots of small files vs. a volume filled with just a few very large files. Finally, you will see better performance with faster/more efficient interfaces — Thunderbolt is faster than Firewire, Firewire 800 is faster than USB 2.0, etc.

Filesystem performance and hardware type

Spotlight Indexing

Find and replace corrupted files

Other applications and conditions that can lead to performance problems

Other backup software copying simultaneously to the same volume, a different volume on the same disk, or across the same interface as CCC's destination.
Utilities that watch filesystem activity and do things when file changes are detected. Antivirus software is a common culprit, but we have also seen problems caused by other watcher applications, such as memeod and Western Digital's SmartWare.
Slow interfaces — USB hubs (including the ports on a USB keyboard or display) and even some USB cables can reduce the bandwidth to your disk dramatically. If you're using USB, be sure that your device is plugged directly into one of the USB ports on your Mac.
Daisy chaining Firewire devices is usually OK, though some enclosures can stall the entire Firewire bus when given too much bandwidth. If you see this behavior, try switching the order of devices in the chain, or attach your backup disk directly to a Firewire port on your Mac.
Using a wireless network connection to connect to a network volume. If you're seeing poor performance with a wireless connection, compare the performance when using a wired (ethernet) connection.

Use the Console application to view the contents of the system log. If you're still having trouble identifying a performance problem, we're here to help.

Automatically prune archived content before copying files

Prune archives in the SafetyNet when free space is less than [xx] GB

If your destination volume has less free space than the limit that you have specified, CCC will prune the oldest archive. CCC will continue to prune the oldest archive until the requested amount of free space has been achieved. Note that if the archives cumulatively consume less space than the limit requested and the destination volume is full, CCC will prune all of the archives.

Auto Adjustment of the SafetyNet Free Space pruning limit

When the Auto Adjust option is enabled (and it's enabled by default), CCC will automatically increase the free space pruning limit if your destination runs out of free space during the backup task. For example, if your pruning limit is set to the default of 25GB, and you have 25GB of free space at the beginning of the backup task, no pruning will be done at the beginning of the task. If that task proceeds to copy more than 25GB of data, however, the destination will become full. CCC will then increase the pruning limit by the larger of either the amount of data copied in the current task, or by the amount of data that was required by the last file CCC attempted to copy. For example, if CCC copied 25GB of data, then the pruning limit would be increased by 25GB. If CCC wanted to copy a 40GB file, however, CCC would not fruitlessly copy 25GB of that file, rather it would immediately increase the pruning limit by 40GB, revisit pruning, and then restart the task.

Prune archives in the SafetyNet when they are older than [xx] days

CCC will prune archives that were created more than "xx" days ago.

Prune archives in the SafetyNet when they are larger than [xx] GB

Starting with the most recent archive, CCC will determine the amount of disk space that each archive consumes. When the cumulative total exceeds the limit that you have imposed, CCC will prune the remaining, older archives. If the newest archive is larger than the limit that you have specified, that archive will be pruned in entirety.

Never prune archives in the SafetyNet

CCC will not automatically prune the contents of the "_CCC SafetyNet" folder at the root of the destination. Archived files may eventually consume all of the free space on the destination, so you should periodically delete older archive folders to maintain enough free space for future backups. You may delete the contents of the SafetyNet folder without harm to the rest of your backup set.

"CCC is pruning my SafetyNet, but the disk is still pretty full at the end of the backup task"

The purpose of CCC's SafetyNet pruning is to make space for additional backups. CCC also avoids pruning items that were very recently archived — after all, it wouldn't make sense to archive an item on the destination, them immediately delete it. To accommodate both of these goals, CCC prunes archives within the SafetyNet before the backup task runs. Pruning the SafetyNet immediately before copying files gives a greater level of assurance that the requested amount of free space (for example) will be available for the current backup. Be sure to consider this detail when specifying your SafetyNet pruning settings. If you want to retain additional space on your backup volume beyond what is required for your CCC backups, specify more liberal limits (e.g. 100GB of free space rather than 25GB).

"Can I use the _CCC SafetyNet folder for long-term archiving of specific items?"

We don't recommend using the SafetyNet for long-term storage. CCC is configured to automatically prune the SafetyNet, by default, when free space on the destination is less than 25GB at the beginning of the backup task, and that limit may increase automatically. CCC doesn't consider whether items in the _CCC SafetyNet folder were placed there by CCC or another application, everything is considered safe to delete when the time is right. If you would like to maintain a permanent archive of items on your backup volume, outside of your CCC backup, we recommend that you create a specific folder for this purpose at the root level of your backup volume.

We also recommend that you maintain a backup of your archived data on another volume! If you don't have a backup of your long-term archived items, you're going to lose them forever if your backup disk fails.

"I manually moved the _CCC SafetyNet folder to the Trash, but now I get an error when trying to empty the Trash"

When CCC backs up your startup disk, it runs with the privileges required to access system files that are not normally accessible to your account. Naturally, some of these files will be updated on the source, and subsequently archived on the destination. When you place these items in the Trash (by placing the _CCC SafetyNet folder in the Trash), and subsequently try to empty the Trash, the Finder typically requests that you authenticate to remove these files. Sometimes the Finder is having a bad day, though, and it simply reports the enlightening "-8003" error when you try to empty the Trash (or something equally obtuse). This error isn't defined or documented anywhere, but through trial and error, we have figured out that it simply means "I can't cope with your request to empty the Trash".

The solution is to avoid using the Finder to delete a CCC SafetyNet folder. Choose Delete a SafetyNet Folder from CCC's Utilities menu instead and use that interface to manually remove SafetyNet folders.

Additional References

Apple Kbase HT201583: You can‘t empty the Trash or move a file to the Trash

Read/write "sparseimage" disk images

A sparseimage disk image is a type of read/write disk image that grows as you copy files to it. In general, sparse disk images only consume as much space as the files they contain consume on disk, making this an ideal format for storing backups. Use of this older disk image format is only recommended when backing up to non-AFP network volumes on an OS older than macOS Sierra. Please note that sparseimage files are monolithic and potentially very large files. If the underlying filesystem has a 2TB file size limit and the sparseimage file reaches that limit, the sparseimage file cannot be grown. In most of these cases the sparseimage file becomes corrupted when the underlying filesystem limit is reached, so we don't recommend this disk image format for large data sets.

Read/write "sparsebundle" disk images

A sparse bundle disk image is similar to a sparseimage insofar as it grows as you add data to it, but it retains its data in many smaller files inside of a bundle rather than inside a single file. We recommend this disk image format for most scenarios.

Running out of space on a sparseimage or sparsebundle disk image

CCC reported that the destination is full, but the underlying disk has plenty of free space. CCC initially sets the capacity of your disk image to the amount of free space on the underlying disk. If you have freed up some space on that disk since you created the disk image, you can manually expand the capacity of the destination disk image in Disk Utility. Choose Resize... from the Images menu in Disk Utility, select your destination disk image, then expand it as desired. We recommend that you do not expand the disk image such that it is larger than the capacity of the underlying disk.

The disk image file is larger than the amount of data it contains, why? Sparseimage and sparsebundle disk images grow as you add data to them. They do not, however, automatically shrink when files are deleted from them. As a result, the amount of disk space that the disk image file consumes will not necessarily reflect the amount of data that they consume. To reclaim disk space that is occupied by the free space on your sparse disk image, CCC will compact the disk image before attempting to mount it if the free space on the underlying volume is less than 25GB, or is less than 15% of the total disk capacity. In most cases, you do not need to compact the disk image yourself, but this functionality is documented here so you'll understand why you might see CCC spending time "Compacting the destination disk image" at the beginning of a backup task.

If you would like to compact a disk image manually, drop the disk image file onto this application: Compact Sparse disk images. Be sure to unmount the disk image volume if it is already mounted. Also, note that the compacting process can take a while (e.g. an hour for a 100GB disk image on a locally-attached volume). Finally, be sure that your system is running on AC power. The system utility that compacts the disk image will refuse to run while the system (e.g. a laptop) is running on battery power.

Read-only disk images

Read-only disk images cannot be modified without invalidating the built-in checksum, therefore they are a good container for storing archived material. Compression rates vary on the content of your source, but you can typically expect to reduce the size of your disk image by about half when using compression. There is a subtle behavior that you should take note of when considering this option as a space-saving measure: CCC will first create a read/write disk image, copy the selected items to it, then convert the disk image to read-only compressed. In this case, you will actually need twice the space on your destination as the items to be copied consume on the source.

Encrypting disk images

If any of the data that you are backing up is sensitive, and if your backup device may be in an insecure location, encrypted disk images can improve the security of your backup. CCC offers 128 bit and 256 bit AES encryption to encrypt disk images. To create an encrypted disk image, select one of the encryption levels from the Encryption menu. After you click on the OK button, you will be prompted to specify a passphrase for the new disk image, and CCC will give you an opportunity to save the passphrase in your own keychain. CCC will also store the passphrase in a private keychain so the disk image can be mounted automatically during scheduled backup tasks.

Note: If you create a read-only, encrypted disk image, the intermediate disk image that CCC creates is NOT encrypted. This intermediate disk image file is deleted once the final, read-only, encrypted disk image has been created, but it is not shredded. Take this into consideration when choosing your destination media. If the destination may be placed in an insecure location, use Disk Utility to securely erase free space on the underlying destination volume after you have created your encrypted disk image archive.

Running a backup task whose destination is a disk image on the startup disk

If you specify a disk image that resides on your startup disk as the destination to a scheduled task, CCC will impose some more conservative requirements on this task. To proceed with this configuration, one of the following requirements must be met:

The amount of free space on the startup disk is at least 1GB larger than the amount of consumed space on the source volume.
The disk image won't grow, e.g. it is a .dmg file, not a sparseimage or sparsebundle disk image.

These requirements avoid a scenario in which the startup disk runs out of free space, causing instability on macOS. If you cannot accommodate the free space requirement, we recommend that you create a .dmg disk image in Disk Utility (choose File > New... > Blank Disk image, set the image format to read/write disk image). Disk Utility will pre-allocate exactly as much space as you request, and CCC will gladly use this disk image without fear of filling up the startup disk.

Sparsebundle disk images are not supported on some filesystems

If your Mac is running an OS older than macOS Sierra, CCC will refuse to save or mount a sparse bundle disk image if the underlying filesystem that the disk image file resides upon does not support the F_FULLFSYNC file control. Most filesystems support this file control, but the SMB file sharing protocol does not. Most people that encounter issues with creating a sparsebundle disk image on a network volume are encountering issues because the network volume is mounted via SMB.

Starting in Mavericks, Apple's preferred file sharing service is SMB. As a result, if you attempt to connect to a network volume, Finder will use SMB to establish that connection unless you explicitly specify AFP as the protocol to use. In this configuration, a sparse bundle disk image will not work, and CCC will issue an error. To avoid this error, connect to the network volume explicitly using AFP:

Eject the network volume if it is currently mounted
Choose Connect to server from the Finder's Go menu
Type in "afp://yourserver.local" (changing the hostname, of course), then click the Connect button and mount the network volume
Go back to CCC and choose Choose disk image... from the Destination selector, then select the sparsebundle disk image on your network volume

Why can't I use a sparsebundle disk image on a filesystem that does not support the F_FULLFSYNC file control?

When your computer writes a file out to the hard drive, the data usually goes to a "write buffer"— a small portion of RAM that is installed on the circuit board of the hard drive. By accumulating smaller write operations onto this RAM chip, the hard drive can increase overall write performance by writing large blocks of cached data to the physical media all at once. While this write buffer improves performance, it also carries a risk. If the power fails or the disk's connection to the computer is suddenly broken between the time that data was written to the buffer and when the buffer is flushed to the disk, your filesystem will have an inconsistency. Filesystem journaling typically mitigates this risk, however it doesn't offer enough protection for Apple's sparsebundle disk image type.

In Mac OS 10.5, Apple implemented the F_FULLFSYNC file control for network servers and clients. The F_FULLFSYNC file control is a command that is sent to the hard drive after some (or all) write operations that tells the disk to immediately flush its cache to permanent storage. To provide better protection for data on sparsebundle disk images, Apple disabled support on Mac OS 10.6 for using sparsebundle disk images that reside on filesystems that do not support the F_FULLFSYNC file control. Apple relaxed this requirement in macOS 10.12 (Sierra).

You are likely to encounter this error condition if your sparse bundle disk image is hosted on a pre-Mac OS 10.5 Macintosh or various Network Attached Storage (NAS) devices (especially SMB). When you encounter this error, copy the sparsebundle disk image to another network volume, or ask CCC to create a new sparseimage disk image file (sparseimage disk images are not the same as sparsebundle disk images).

A message for new Mac users coming from the Windows world

Backups on a Windows system are very different from those on a Macintosh. If you're coming from a Windows background, the term "imaging" and the concept of making a disk image backup is probably familiar to you. Restoring from disk image backups is made simpler on Windows because the startup environment is built around them. That's not the case for a Macintosh. When you create a disk image backup of your Mac's startup disk, the logistics of restoring that backup are actually fairly complicated. Due to these complications, we don't recommend using a disk image as your primary backup on a Mac. Disk images are useful for storing a backup of your user data on a network volume, but for your Mac's startup disk, we recommend that you back up directly to a disk that is attached to your Mac; not to a disk image.

Support for APFS-formatted disk images is suspended until Apple resolves a serious data loss problem

Recently we discovered a very serious data loss bug in macOS High Sierra involving APFS-formatted sparse disk images residing on a volume with very little free space. Unlike HFS+ formatted disk images, APFS formatted disk images will not adjust their free space to reflect the true amount of free space available on the underlying volume. Additionally, if you attempt to copy more data to the disk image volume than the underlying disk can accommodate, the APFS filesystem on the disk image fails to report an error — the copy task to the disk image appears to succeed without error, despite the data never actually being written to disk. This is an error condition that a file copier (Finder, CCC, any utility that writes files to the disk image) cannot detect, therefore it cannot report the condition to the user (again, because everything looks OK to the file copier). As a result, we are suspending support for APFS-formatted disk images until Apple resolves this problem.

Regretfully, we did not discover Apple's bug prior to offering support for creating APFS-formatted disk images. Starting in CCC 5.0.4 and up to CCC 5.0.8, the "New disk image..." option in CCC's destination selector would create an APFS-formatted disk image automatically if the source volume was APFS-formatted. Starting in 5.0.9, CCC will issue an error for any task that backs up to an APFS-formatted disk image. Especially if the underlying destination is full or nearly full, we strongly recommend that you heed CCC's advice to delete the APFS-formatted destination disk image. Choose "New disk image..." from CCC's Destination selector to create a new disk image. CCC will automatically create the disk image using Apple's legacy (and trusted for sparse images) HFS+ format.

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Frequently Asked Questions (FAQ)

Advanced Topics

Does CCC have to be running for a scheduled task to run?

No. Once you have saved your tasks, you can quit CCC. Even if tasks are running, it's OK to quit CCC -- they will continue to run. A helper application, named "com.bombich.ccchelper" will be running quietly in the background, handling task operations. This helper application also loads automatically when you restart your computer, so you don't have to launch CCC again unless you want to make changes to your task configurations or scheduling.

What happens if no one is logged in when a task is scheduled to run?

The scheduled task will run whether someone is logged in to the machine or not. You can also log in or log out while tasks are running and the tasks will continue to run.

Will CCC run when the computer is turned off?

If your backup task is configured to "Wake or power on the system", CCC will schedule a "Wake or power on" event with the Power Management service and your system will turn on shortly before the task is scheduled to run.

FileVault exception

There is one notable exception to powering on the system for a scheduled task: If you have FileVault enabled on your startup disk, your computer would turn on, but it would not proceed past the FileVault authentication prompt. It is not possible for CCC to subvert this security feature, so the Wake or power on the system option will be disabled if FileVault is enabled on your startup disk. This limitation is applicable only when the system is turned off; CCC can wake a system with FileVault protection enabled and proceed to run a backup task.

Will CCC run when the my laptop's lid is closed?

If your laptop is running on battery power, the system will not wake while the lid is closed and CCC backup tasks will not run. If your laptop is plugged in to AC power, then CCC can wake the system to start your scheduled task if the lid is closed. See the section above for the settings that indicate whether a task can wake the system.

How is system sleep handled?

By default, CCC will wake your computer when your tasks are scheduled to run. You can change this setting in the Runtime Conditions section when scheduling a task. As long as your Mac is running on AC power, CCC will prevent the system from sleeping for the duration of a backup task.

Why does my laptop sometimes go to sleep during a backup task?

If your Mac is a laptop, note that CCC will only be able to wake the system or prevent idle sleep if the system is running on AC power. CCC will attempt to thwart sleep while the system is running on battery power, but macOS may sleep the system anyway if there is no user activity while running on battery power.

Why does my screen turn on shortly before a backup task starts?

By default, CCC schedules a wake event to occur 20 seconds before a scheduled task is configured to run. Whether the system is sleeping or not, macOS turns on the display when a scheduled wake event occurs, and there is nothing that CCC can do to prevent this. If you prefer that your display does not turn on, e.g. in the middle of the night, use the Run this task when the system next wakes setting instead to have CCC tasks run during macOS Dark Wake cycles (aka PowerNap, aka Maintenance Wake).

What if the backup disk is not available when a task is scheduled to run?

If your backup disk is attached to your Mac and unmounted, CCC will attempt to mount the backup volume, then proceed with the backup task if that is successful. If the volume cannot be mounted or is not attached to your Mac, CCC will, by default, report an error, then run the task immediately when the backup disk is reattached to your Mac. You can fine-tune CCC's handling of this scenario using the options at the bottom of the Scheduler panel.

Can I stop a backup task before it finishes?

Yes, you can stop the backup task at any time. The next time you run the backup task, CCC will copy only the files that have changed or were missed since the last backup task.

How can I disable/suspend a task?

If CCC's sidebar is not revealed, reveal it by choosing Show Sidebar from CCC's View menu. To disable a task, right-click on that task in the sidebar and choose Disable from the contextual menu. Use the same procedure to re-enable the task. If you would like to disable all tasks, choose Disable all tasks... from the CCC menubar application, or hold down Command+Option and choose Disable All Tasks & Quit from the Carbon Copy Cloner menu.

Defer if another task is writing to the same destination

If you have more than one scheduled task that writes to the same destination volume, you may want to configure the tasks to wait for one another such that only one task is writing to the volume at a time. When you configure a task with this setting and the scheduled run time elapses, CCC will place the task into a queue for deferred execution if another task is already writing to that same destination. Assuming another run time condition does not prevent it, CCC will run the deferred task as soon as the first task finishes writing to the shared destination volume.

Limit which days of the week this task can run

This option allows you to limit a task to running only during weekdays or only during weekend days. This option is not applicable to the "weekly" and "monthly" scheduling settings.

Limit when this task can run

This option allows you to limit a task to running during specific hours of the day. For example, if you don't want your hourly task to run in the afternoons, you could set a start limit of 6PM and an end limit of 12PM. This limit would allow the task to start any time after 6PM and any time up to 12PM, thus preventing the task from running between 12PM and 6PM. If the task is already running (e.g. if it started at 11:55AM), CCC will stop the task if it is still running when the end limit is reached.

Handling system sleep events

By default, CCC will wake your computer when your tasks are scheduled to run. You can change this setting in the Runtime Conditions section of the Scheduler popover. There are four options:

Wake the system

CCC will configure a wake event to wake the system shortly before the task runs, so the task should run on schedule. If the system is turned off, this wake event will not turn on the system.

Wake or power on the system

CCC will configure a wake or power on event to wake the system or turn it on shortly before the task runs, so the task should run on schedule.

Run this task when the system next wakes

Upon a wake notification, CCC will run the backup task if its scheduled run time has passed. The task will not run exactly when it is scheduled, though CCC can run tasks during macOS Dark Wake events (aka PowerNap, aka Maintenance Wake), which occur every couple hours. If you want your backup tasks to run in the middle of the night without turning on your display, this is the right option for you.

Skip this task

CCC will run the task only at its scheduled run time if the system is awake at that time. Upon a wake event, CCC will not run a backup task if the scheduled run time has passed.

Don't send error notifications

By default, CCC will report an error if the source or destination volume is unavailable when the task is scheduled to run. By enabling this option, CCC will suppress these errors. Additionally, if you have configured your task to send an email when errors occur, this option will suppress that email.

This option is not applicable for the When the source or destination is reconnected scheduling setting, because a task configured in that manner will only attempt to run if both the source and destination are present.

Run this task as soon as the missing volume reappears

If a backup task is missed because the source or destination was missing at the scheduled run time, this option will cause CCC to run the backup task as soon as that missing volume reappears.

Can I back up an encrypted volume to a non-encrypted volume?

Yes.

If I back up an encrypted volume to a non-encrypted volume, will the copied files be encrypted on the destination?

No, encryption occurs at a much lower level than copying files. When an application reads a file from the encrypted source volume, macOS decrypts the file on-the-fly, so the application only ever has access to the decrypted contents of the file. Whether your backed-up files are encrypted on the destination depends on whether encryption is enabled on the destination volume. If you want the contents of your backup volume to be encrypted, follow the procedure documented here to enable encryption.

Will Carbon Copy Cloner enable encryption on my backup volume?

No. You can enable encryption in the Security & Privacy preference pane while booted from your bootable backup, or in the Finder by right-clicking on your backup volume.

Do I have to wait for encryption to complete before rebooting from my production volume?

No. Once you have enabled encryption on the backup volume, you can reboot from your production startup disk and the encryption process will continue in the background.

What happens if I change my account password on the source volume? Does the encryption password on the backup volume get updated automatically?

The encryption password(s) on the backup volume will not be automatically updated when you change the password for an account on the source volume. When you boot from the backup volume, you may notice that your user account icon is a generic icon, and the text indicates "[Update needed]". The update that is required is within the proprietary encryption key bundle that macOS maintains for your encrypted volume. This encryption key is not maintained on the backup volume, and it is Apple-proprietary, so it isn't something that CCC can or should modify. To update the encryption password on the destination volume:

Choose the backup volume as the startup disk in the Startup Disk preference pane and restart your computer. You will be required to provide the old password to unlock the volume on startup.
Open the Users & Groups preference pane in the System preferences application.
Click on the user whose password was reset on the source volume and reset that user's password again. Resetting the password while booted from the backup volume will update the encryption key for that user on the backup volume.
Reset the password for any other user accounts whose password was reset on the original source.

I enabled encryption on my 3TB USB backup disk. Why can't I boot from that volume any more?

Some versions of OS X have difficulty recognizing USB devices that have been encrypted with FileVault. The Western Digital My Passport Ultra 3TB disk, for example, works fine as a bootable device when not encrypted. In our tests, however, this device was no longer recognizable when FileVault encryption was enabled. This problem appears to be limited to OS X 10.11 El Capitan. The same volume was accessible using older and newer OSes, and also functioned fine as an encrypted startup device using older and newer OSes.

I formatted my destination as encrypted, and it's bootable. Why do you recommend cloning to a non-encrypted volume first?

We generally recommend that people establish a bootable backup on a non-encrypted volume, and then enable FileVault while booted from the destination. Some people have discovered, however, that a pre-encrypted volume can (will usually) function as a bootable device. So why do we recommend the former? There are a couple notable differences between pre-encrypting the disk vs. enabling FileVault after booting from the not-encrypted disk. When you enable FileVault via the Security Preference Pane:

You get a sanity check that a recovery volume exists (this avoids spending lots of time copying files only to find out that the volume might not be bootable)
You get the opportunity to store a recovery key with Apple
You can unlock the disk with selected accounts
You get a nicer UI on startup to unlock the disk (e.g. it's similar to the LoginWindow interface), vs. a less-polished looking Unlock Disk interface

One drawback to enabling FileVault via the Security Preference Pane, however, is that changes to account passwords on the source volume aren't immediately reflected on the backup as far as unlocking the disk is concerned. The old account passwords would be required until you boot from the backup and specifically re-enable those accounts in the Security Preference Pane (at which time the disk's EncryptionKey is remastered).

As far as the backups are concerned, there's no difference between these two methods. There is still an order-of-operations concern with pre-encrypting the disk if your disk is formatted using Apple's legacy HFS+ filesystem format (the steps below are not applicable to APFS – with APFS, simply erase the disk as an encrypted APFS volume in Disk Utility). You'd want to approach it in this manner:

Erase the destination device (unencrypted!)
Click on the freshly-erased disk in CCC's sidebar and create a recovery volume on that disk
Go back to Disk Utility and erase the volume now, not the whole disk (as was emphasized in the instructions above). Now you can choose the option to encrypt the volume. By erasing just the volume here, not the whole disk, the hidden recovery partition that CCC created won't be destroyed.
Open CCC and configure your backup task

In general, either procedure is fine, it really is the same as far as the backup is concerned. We generally prefer the Security Preference Pane method, however, because it yields the same UI behavior you are expecting if you have enabled FileVault on your production startup volume. Many people become concerned when the Disk Utility-encrypted volume shows any behavioral difference at all with regard to unlocking the disk on startup, and that concern is best avoided by enabling FileVault in the Security Preference Pane.

I restored my backup to another Mac that had FileVault enabled, and now I can't unlock the cloned volume.

Encryption is a volume-specific endeavor, and when it's enabled via FileVault, it's also tied to the user accounts on that specific installation of macOS. If you clone another installation of macOS onto a volume that has FileVault enabled, the user accounts from the "foreign" (source) OS will not be able to unlock the FileVault-encrypted destination volume. To avoid this scenario, you should erase the destination volume as a non-encrypted volume. When erasing an APFS volume, be careful to erase the whole APFS container, not just the encrypted volume within the container.

Please note that this concern is not applicable to restoring a backup to the original source volume. In that case, the OS on the backup volume is not foreign; the user accounts on the backup volume match the user accounts on the original source. In that scenario, FileVault will continue to function normally.

I haven't enabled FileVault, why does CCC indicate that the SSD in my T2-based Mac is encrypted?

New Macs that have Apple's T2 controller chip (e.g. the iMac Pro and the Mid-2018 MacBook Pro) support new security measures for the internal startup disk. When volumes on that disk are formatted as APFS, those volumes intrinsically benefit from at-rest encryption. A password is not required to unlock these volumes (that password is "baked" into the Mac's hardware), but the volume is encrypted automatically.

The Startup Security Utility may not work correctly after restoring to an encrypted-at-rest volume on T2-based Macs

The at-rest encryption described above involves a volume-specific "secure access token", which each user account must obtain access to if that user requires administrative privileges over startup security settings. Because this token is volume-specific, cloning the token from one volume to another will not produce the correct result. Additionally, user accounts that have access to the token on the source won't automatically have access to the token on a cloned volume.

Apple does not offer a method for creating this token on a volume that is not the current startup disk, so CCC cannot offer a postflight method that automatically creates that token. Apple does, however, offer a utility for creating the token on the current startup disk, and also for granting access to that token for specific users on the current startup disk. If you find that you're unable to modify settings in the Startup Security Utility while booted from the macOS Recovery volume (e.g. "No administrator was found"), reboot from your cloned volume, then paste the following into the Terminal application to create the secure access token and grant access to it to your user account (replace "yourname" with the short name of your user account):

sysadminctl interactive -secureTokenOn yourname -password -

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Advanced Topics

Mounting the source or destination volume before a backup task begins

Little Snitch may prevent the automated mounting of network volumes

If you're using Little Snitch to monitor and filter your inbound and outbound network traffic, you may find that CCC has trouble automatically mounting a network volume. If you run into this problem, configure Little Snitch to allow network access to the NetAuthSysAgent system service. NetAuthSysAgent is the macOS system service that fulfills application requests to mount network volumes.

SafetyNet Pruning

SafetyNet pruning is covered in more detail in this section of CCC's documentation.

Destination volume options

Power management options

Turn off the computer if it was previously off

Power Management options are ignored in some cases

Power Management options are applied regardless of task success

Run another backup task (task chaining)

Running shell scripts before and after the backup task

CCC passes several parameters to pre and post clone shell scripts. For example, the following shell script:

Would produce the following output (you can redirect this output to a file of your own specification) if implemented as a post clone script:

Running /Library/Application Support/com.bombich.ccc/Scripts/postaction.sh Wed Oct 8 21:55:28 EDT 2014 Source: / Destination: /Volumes/Offsite Backup Third argument: 0 Fourth argument:

First parameter

The path to the source volume or folder.

Second parameter

The path to the destination volume or folder. If the destination is a disk image, this is the path to the mounted disk image.

Third parameter

Pre clone script: The underlying mountpoint for the volume that holds the destination disk image, if applicable.
Post clone script: The exit status of the file copying phase of the backup task.

Fourth parameter

The path to the destination disk image, if applicable.

If your postflight script exits with a non-zero exit status, CCC will not report this as a failure of the backup task. The failure will be noted in the Task History window, however.

AppleScripts are not supported

You cannot specify an AppleScript as a pre or post clone script, CCC currently only supports running shell scripts.

Shell scripts require a shell interpreter line

Security implications of pre and post clone shell scripts

chmod 755 /Library/Application\ Support/com.bombich.ccc/Scripts/*.sh

Example pre and post clone shell scripts

To use any of these example scripts, download the script and place it somewhere on your startup disk. By default, CCC looks in /Library/Application Support/com.bombich.ccc/Scripts.

play_sound.sh
If you want to play a unique sound, use this script. You can plug in the path to any audio file of your liking or try one of the examples included.

post_to_slack.sh
This postflight script will post the status of your backup task to a Slack channel.

ifttt_maker.sh
This postflight script will post an IFTTT Maker Event of the status of your backup task.

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Advanced Topics

To back up to a new disk image:

Choose your source volume from the Source selector
Choose New disk image... from the Destination selector
Provide a name and choose a location to save your disk image
If you plan to back up to this disk image again in the future, set the image format to one of the read/write formats. If you want a read-only disk image for archival purposes, set the image format to one of the read-only formats.

To back up to an existing disk image, select Choose disk image... from the Destination selector and locate your disk image.

Read/write "sparseimage" disk images

Read/write "sparsebundle" disk images

Running out of space on a sparseimage or sparsebundle disk image

Read-only disk images

Encrypting disk images

Running a backup task whose destination is a disk image on the startup disk

The amount of free space on the startup disk is at least 1GB larger than the amount of consumed space on the source volume.
The disk image won't grow, e.g. it is a .dmg file, not a sparseimage or sparsebundle disk image.

Sparsebundle disk images are not supported on some filesystems

Eject the network volume if it is currently mounted
Choose Connect to server from the Finder's Go menu
Type in "afp://yourserver.local" (changing the hostname, of course), then click the Connect button and mount the network volume
Go back to CCC and choose Choose disk image... from the Destination selector, then select the sparsebundle disk image on your network volume

Why can't I use a sparsebundle disk image on a filesystem that does not support the F_FULLFSYNC file control?

A message for new Mac users coming from the Windows world

Support for APFS-formatted disk images is suspended until Apple resolves a serious data loss problem

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Advanced Topics

Carbon Copy Cloner maintains a list of certain files and folders that are automatically excluded from a backup task. The contents of this list were determined based on Apple recommendations and years of experience. The following is a list of the items that are excluded along with an explanation of why they are excluded.

Legend:
Items prefixed with a "/" indicate that they will only be ignored if located at the root of the volume.
Items postfixed with a "/*" indicate that only the contents of those folders are ignored, the folders themselves will be copied.
Items postfixed with a "*" indicate that the filename will be matched up to the asterisk.

Filesystem implementation details

.HFS+ Private Directory Data*
/.journal
/.journal_info_block
.afpDeleted*
._*
.AppleDouble
.AppleDB
/lost+found
Network Trash Folder
.TemporaryItems

These items only show up if you're running an older OS than what was used to format the source volume, and on some third-party implementations of AFP and SMB network filesystems. These items should never, ever be manipulated by third-party programs.

Volume-specific preferences

.metadata_never_index
.metadata_never_index_unless_rootfs
/.com.apple.timemachine.donotpresent
.VolumeIcon.icns
/System/Library/CoreServices/.disk_label*
/TheVolumeSettingsFolder

These items record volume-specific preferences, e.g. for Spotlight, Time Machine, and a custom icon for the volume. Feedback on the exclusion of these items is welcome. Because they are volume-specific preferences, the exclusion of these items from a day-to-day backup seems most appropriate.

Apple-proprietary data stores

.DocumentRevisions-V100*
.Spotlight-V100
/.fseventsd
/.hotfiles.btree
/private/var/db/systemstats

These items are Apple-proprietary data stores that get regenerated when absent. Attempting to copy these data stores without unmounting the source and destination is not only futile, it will likely corrupt them (and their respective apps will reject them and recreate them).

The DocumentRevisions data store is used by the Versions feature in macOS. The Versions database stored in this folder contains references to the inode of each file that is under version control. File inodes are volume-specific, so this dataset will have no relevance on a cloned volume.

Volume-specific cache files

/private/var/db/dyld/dyld_*
/System/Library/Caches/com.apple.bootstamps/*
/System/Library/Caches/com.apple.corestorage/*

Copying these caches to a new volume will render that volume unbootable. The caches must be regenerated on the new volume as the on-disk location of system files and applications will have changed. macOS automatically regenerates the contents of these folders when CCC is finished updating the backup volume.

NetBoot local data store

/.com.apple.NetBootX

In the unlikely event that your Macintosh is booted from a Network device, macOS will store local modifications to the filesystem in this folder. These local modifications are not stored in a restorable format, therefore should not be backed up. In general, you should not attempt to back up a NetBooted Mac.

Dynamically-generated devices

/Volumes/*
/dev/*
/automount
/Network
/.vol/*
/net

These items represent special types of folders on macOS. These should not be backed up, they are dynamically created every time you start the machine.

Quota real-time data files

/.quota.user
/.quota.group

When these files are copied to a destination volume using an atomic file copying procedure, the macOS kernel will prevent the destination from being gracefully unmounted. The contents of these files is never accurate for the destination volume, so given the kernel's unruly behavior with copies of these files, CCC excludes them. According to the quotacheck man page, these files should be regenerated every time a quota-enabled volume is mounted (e.g. on startup). We have not found that to be consistently true. If you're using quotas, run sudo quotacheck / after restarting from your backup volume or a restored replacement disk to regenerate these files.

Large datastores that are erased on startup

/private/var/vm/*
/private/tmp/*
/cores

macOS stores virtual memory files and your hibernation image (i.e. the contents of RAM are written to disk prior to sleeping) and temporary items in these folders. Depending on how you use macOS and your hardware configuration, this could be more than 50GB of data, and all of it changes from one hour to the next. Having this data for a full-disk restore does you absolutely no good — it makes the backup and restore processes take longer and the files get deleted the next time you boot macOS.

Trash

.Trash
.Trashes

Moving an item to the trash is typically considered to be an indication that you are no longer interested in retaining that item. If you don't want CCC to exclude the contents of the Trash, you can modify each task's filter:

Choose Copy Some Files from the popup menu underneath the Source selector
Click the Inspector button adjacent to that same popup menu to reveal the Task Filter window
Uncheck the box next to Don't copy the Finder's Trash
Click the Done button

Time Machine backups

These folders store Time Machine backups. Time Machine uses proprietary filesystem devices that Apple explicitly discourages third-party developers from using. Additionally, Apple does not support using a cloned Time Machine volume and recommends instead that you start a new Time Machine backup on the new disk.

/Backups.backupdb
/.MobileBackups
/.MobileBackups.trash
/.MobileBackups.trash

Corrupted iCloud Local Storage

iCloud leverages folders in your home directory for local, offline storage. When corruption occurs within these local data stores, macOS moves/renames the corrupted items into the folders indicated below. macOS doesn't report these corrupted items to you, nor does it attempt to remove them. CCC can't copy the corrupted items, because they're corrupted. To avoid the errors that would occur when trying to copy these corrupted items, CCC excludes the following items from every backup task:

Library/Mobile Documents.*
.webtmp

Special files

Files included in this section are application-specific files that have demonstrated unique behavior. The kacta and kactd files, for example, are created by antivirus software and placed into a special type of sandbox that makes them unreadable by any application other than the antivirus software.

The last item can be found in each user home folder. Excluding this item prevents the applications that were open during the backup task from opening when you boot from the backup volume. This seems appropriate considering that Apple intends the feature to be used to open the applications that were in use when you log out, restart or shutdown, not at an arbitrary point during the backup task.

/private/tmp/kacta.txt
/private/tmp/kactd.txt
/private/var/audit/*.crash_recovery
/private/var/audit/current
/Library/Caches/CrashPlan
/PGPWDE01
/PGPWDE02
/.bzvol
/.cleverfiles
/Library/Application Support/Comodo/AntiVirus/Quarantine
/private/var/spool/qmaster
$Recycle.Bin
Library/Preferences/ByHost/com.apple.loginwindow*

CCC SafetyNet folders

When CCC's SafetyNet feature is enabled, CCC creates a _CCC SafetyNet folder at the root of the selected destination volume or folder. When CCC encounters an item on the destination that does not exist on the source, or an item that will be replaced with an updated item from the source, that item gets placed into the SafetyNet folder rather than being deleted immediately. The SafetyNet folder is literally a safety net for files on your destination. If you accidentally delete a file from the source and you don't realize it until after your backup task runs, you'll find the item in the SafetyNet folder. Likewise, if you accidentally specify the wrong volume as a destination to a CCC backup task, the mistake does not catastrophically delete every file from the selected destination; you simply recover the items from the _CCC SafetyNet folder.

The protection that the SafetyNet folder imparts is specific to the volume upon which the SafetyNet folder resides. As such, CCC never includes the contents of the _CCC SafetyNet folder in a backup task. So, for example, if your hard drive fails and you restore your backup to a replacement disk, the _CCC SafetyNet folder is automatically excluded from that restore task. This exclusion is applicable to any folder with the "_CCC" prefix. If you have several tasks backing up to separate folders on a backup volume, for example, the _CCC SafetyNet folders that are created in those subfolders would not be included in a secondary backup task that copies your backup disk to a third disk.

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Advanced Topics

Carbon Copy Cloner offers the option of securely copying your selected data to another Macintosh on your network (or anywhere on the Internet for that matter) via the Remote Macintosh... options in the Source and Destination selectors. After a brief setup procedure to establish trust between your Mac and the destination Mac, simply choose the source or destination volume/folder on the remote Mac and CCC will take care of the rest.

Before setting up CCC to back up to a remote Macintosh, you must:

Confirm that the remote Macintosh is running a supported OS (OS X 10.7 or later)
Enable Remote Login in the Sharing Preference Pane on the remote Macintosh
Verify that any firewalls between the two Macs are permitting "secure shell" traffic over port 22 (or a custom port that you specify).

Enabling Remote Login on the remote Macintosh

To enable Remote Login on your remote Macintosh:

Log in to that machine as an admin user.
Open the System Preferences application.
Open the Sharing Preference Pane.
Check the box next to Remote Login.
Be sure to allow access to All users, or explicitly add the Administrators group to the list of restricted users and groups.
Make a note of your remote Mac's hostname. The hostname is indicated underneath the Computer Name text field. In the screenshot below, "Apollo.local" is the hostname of the remote Macintosh.

Configuring a Remote Macintosh source or destination

With the Remote Login service enabled on the remote Mac, the next step is to choose Remote Macintosh... from CCC's Source or Destination selector. CCC will present a browser that lists any hosts on your local network that advertise the Remote Login service. Find and select your remote Mac in this list, then click the Connect button. If you do not see your Mac listed here, type in the hostname of your remote Mac, then click the Connect button. If the remote Mac is not on your local network, you may need to specify the IP address of the public-facing router that your Mac resides behind. Be sure to configure the router to forward port 22 traffic to the IP address that is assigned to the remote Mac.

Connect to host

Once CCC has established a connection to the remote Mac, you will be prompted to install a Mac-specific Public Key Authentication (PKA) key pair onto the remote Mac. You must provide the username and password of an admin user on the remote Mac to permit this, and that admin user must have a non-blank password. Those requirements are only for the initial public key installation. For future authentication requests, CCC will use the PKA key pair.

Authenticate to the remote Mac

Install Key

Once you have connected to the remote Mac and installed CCC's key on that system, CCC will present a volume browser. Select the volume or folder to use as the source or destination for your task. Note: avoid selecting a volume or folder that contains an apostrophe (').

Connect to host

Bandwidth management options

CCC offers two options that can help you address bandwidth concerns. The option to Compress data passed over the network can greatly reduce your backup time and total bandwidth used. The time savings depend on just how slow the connection is between the two Macs. If you have a connection that is slower than 10MB/s, compression will make the transfer faster. If your bandwidth is better than that, compression may actually slow down your transfer. CCC will not compress certain file types that are already compressed, such as graphics files, movies, and compressed archives. Specifying the option to compress data passed over the network does not create a proprietary or compressed backup; files are automatically decompressed on the destination volume on the remote Macintosh.

CCC also offers a bandwidth limitation option. If your ISP requires that your transfers stay below a certain rate, you can specify that rate here. Note that CCC errs on the conservative side with this rate, so the average transfer rate may be slightly lower than the limitation that you specify.

De-authenticating a remote Macintosh

If you no longer wish to use a particular remote Macintosh, you can click the Deauthenticate... button to remove CCC's PKA key pair from the remote Mac.

Remote Macintosh prerequisites

At this time, CCC requires the use of the root account (though it does not have to be enabled) on both the source and destination Macs. To successfully back up to a remote Macintosh, you must have administrative privileges on both machines.

CCC also requires that the remote Macintosh be running macOS 10.7 or later. Non-Macintosh systems are not supported with the Remote Macintosh feature.

Note for Yosemite, El Capitan, & Sierra users: If your source contains macOS Yosemite (or later) system files, the Remote Macintosh must be running macOS 10.9.5 or later. If the Remote Macintosh is not running 10.9.5 or later and you attempt to back up macOS Yosemite (or later) system files, the backup task will report numerous "Input/output" ("Media") errors. Filesystem changes introduced on Yosemite cannot be accommodated by older OSes. Apple added support for those filesystem changes in 10.9.5 to offer a modest amount of backwards compatibility.

Additional pointers for advanced users

Carbon Copy Cloner's public key-based authentication is designed to work with no additional configuration of the services required for backing up over a network connection. CCC uses rsync over an ssh tunnel to perform the backup. If you do make modifications to the sshd configuration, you should consider how that may affect your backup. For example, CCC requires use of the root account over ssh. If you set the "PermitRootLogin" key in the sshd_config file to "no", you will not be able to use CCC to or from that machine. It's an important distinction to note that the root account does not have to be enabled, but sshd must permit the use of the root account. The "PubkeyAuthentication" key must also not be set to "no", because Public Key Authentication is required for CCC to authenticate to the remote Mac. CCC will attempt to proactively present these configuration scenarios to you if authentication problems are encountered.

Additionally, the initial Public Key Authentication (PKA) setup requires the use of an admin user on the remote Macintosh. That admin user account must have a non-blank password, and the Remote Login service must permit password-based authentication. These requirements apply only to the initial installation of CCC's PKA credentials. Once CCC has installed these credentials on the remote Mac, CCC will use PKA for authentication to the remote Mac.

Troubleshooting connectivity problems to a remote Macintosh

Problems connecting to a remote Macintosh generally are caused by configuration problems with the Remote Login service on the remote Macintosh. Try the following if you are having trouble making a backup to a remote Mac:

Verify that the Remote Login service is enabled in the Sharing preference pane on the Remote Macintosh.
Verify that access to the Remote Login service is allowed for All users.
Re-select Remote Macintosh from CCC's Source or Destination selector and verify that authenticaiton to the remote Mac is configured.
Verify that your firewall and the remote Mac's firewall permits traffic on port 22. If you have an application firewall in place (e.g. Little Snitch), verify that access is granted to CCC's privileged helper tool, "com.bombich.ccchelper".
If your local Mac and remote Mac are not on the same network (e.g. you're connecting across a VPN or through a router and over the Internet), confirm that a connection can be established between the two Macs. How you do this will vary from one scenario to the next, but you can generally verify connectivity by typing "ssh root@192.168.1.1" into the Terminal application (replace 192.168.1.1 with the hostname or IP address of your remote Mac). If you see a request for a password, then connectivity is established. If not, your network configuration isn't permitting the traffic, or the hostname that you're connecting to is invalid or unavailable. If you are accessing a remote Mac that is behind a router, consult the router's port forwarding documentation and verify that port 22 traffic is directed to the internal IP address of the remote Mac.

VPN and port forwarding configuration is outside of the scope of support for CCC, though our support staff will make every effort to identify whether problems are occurring within that configuration or within the service configuration on your remote Mac. If you have worked through the troubleshooting steps above and are still having trouble backing up to a remote Macintosh, please choose Report a problem from CCC's Help menu and submit a support request.

Meraki router intercepts Secure Shell traffic

Some users that have a Meraki router involved in their configuration have reported that its default configuration will interrupt Secure Shell traffic. The firewall rule that causes interference is in place to protect the network from vulnerabilities that are irrelevant between two modern Macs. Nonetheless, the firewall intercepts traffic after initially allowing a connection, which is presented by CCC as a "lost connection" or a failure to authenticate to the remote Mac. The following steps correct the Meraki configuration concern:

Log into the Meraki as an administrative user and open the "Security report"
Filter the log for SSH events
Click the "SSH_EVENT_REPOVERFLOW" event from the list to open it and review the blocked event
To allow the blocked traffic of this type, click "Yes" to add this event to the whitelist.

Thomson Gateway router intercepts Secure Shell traffic

Similar to the problem described above for Meraki router, the Thomson Gateway router can also cause interference that appears as an authentication failure. Forwarding traffic to a non-standard secure shell port (e.g. 2222, then be sure to specify that port when connecting to the Remote Macintosh in CCC) resolves the problem.

A note about access privileges to backed up data

While logged in to your remote Macintosh, you may not have permission to view the contents of your backup in the Finder. Your access to the files will be based on the unique id that is associated with the user account that you're logged in to on the remote Macintosh and the one associated with the account(s) on the other Mac(s) that you're backing up. The first administrator account always gets a uid of "501", and subsequent accounts are assigned incrementally higher uids — 502, 503, etc. For security and privacy purposes, macOS restricts access to the contents of user home directories to the owners of those home directories, and these restrictions are preserved when your data is backed up to a remote Macintosh.

To learn what user id is associated with your account:

Open System Preferences and click on the User Accounts preference pane.
Click on the lock and authenticate.
Control+click on your account in the accounts table and choose "Advanced options".

You will see your User ID in the panel that appears.

This may be annoying from the perspective of trying to access those files on your remote Macintosh, but it is important for CCC to preserve the ownership and permissions information when backing up your data. If/when you want to do a restore, you could do either of the following:

a) Attach the external drive directly to the machine that you want to restore files to — the accounts on those systems will be able to access their backed up files.

b) Do a restore directly within CCC from the original source Macintosh.

If you must have read access to some of this data (e.g. the original Mac is gone, the user account changed, etc.), you can change the ownership of the home folder and its contents in the Finder:

Choose Get Info from Finder's File menu.
In the Sharing and Permissions section at the bottom, click on the lock icon to make the permissions editable.
Click on the + button.
In the window that appears, select your account, then click the Select button.
Set the access privileges to Read & Write.
Click on the Gear menu and choose to apply the change to enclosed items.

Default Filter Behavior

Include everything by default: Define what is excluded

Exclude everything by default: Define what is included

Calculating disk usage and Protected Size

Source and destination options

By default, CCC won't copy the contents of the Finder Trash because, well, it's Trash. If you want CCC to back up your Trash, uncheck the Don't copy Finder's Trash box to remove the exclusion.

Excluded files are not deleted from the destination

Please carefully consider the scope of effect that this option will have when using the Exclude everything by default filter behavior.

The Protect root level items setting is described in more detail in the Advanced Settings article.

Custom Filters

Anchored path filter

Subpath filter

Wildcard characters

Expert settings

Including folders and their content with the 'Exclude everything by default' filter behavior and custom rules

/Users/johnny/Pictures.Photos Library.photolibrary**

Exporting and Importing filters

Items automatically excluded

Online-only files can't be backed up

Dropbox Professional offers a "Smart Sync" feature that allows the user to store files only in the cloud. What remains on your Mac is a 0-byte placeholder file. If you attempt to open the placeholder file, Dropbox automatically downloads the data of the file to your Mac and the document opens. While this is a convenient feature that allows you to free up some space on your Mac, this feature removes files from your local storage, which means that CCC can't make a backup of these online-only files. Before using the Smart Sync feature, you should consider whether you are comfortable with not having a local backup of the files that you choose to store only in the cloud.

Dropbox placeholder files are backed up as placeholder files

When you ask Dropbox to store a file only in the cloud, Dropbox deletes the local copy of the file and replaces it with a proprietary, 0-byte placeholder file. As noted above, when you open a placeholder file in the Finder, Dropbox downloads the original. Likewise, if you attempt to copy a placeholder file via the Finder from one volume to another, Dropbox downloads the data to the source, then copies the original file (leaving the downloaded source file in place). CCC backups do not behave like Finder copies. And for good reason – if you have 1TB of online-only files on your 500GB SSD, you wouldn't want Dropbox to download all of that data when CCC attempts to make a backup! Rather, CCC copies the placeholder files as they are, retaining all of the placeholder attributes of the source files. CCC makes a non-proprietary backup of your files; our goal is to make the destination files look exactly like the source files.

Dropbox's proprietary placeholder files are not transferrable from APFS to HFS+ formatted volumes

If your Dropbox folder is on an HFS+ formatted volume (the default filesystem up to macOS Sierra), Dropbox will flag an online-only placeholder as a compressed file. The file is not technically compressed, of course, because no data is stored locally. This clever hack works, but this is an unconventional use of the "is compressed" file flag. As far as backing up these files is concerned, though, the hack is fine – CCC will preserve these placeholder files when copying to another HFS+ volume, or even to an APFS volume.

If your Dropbox folder is on an APFS volume (the default filesystem starting in macOS High Sierra), then Dropbox creates a sparse placeholder file. A sparse file has a logical size that is larger than its physical size. In the case of a Dropbox placeholder file, the logical size would be the size of the real file (e.g. 2.4MB), and the physical size would be 0 bytes (because no data is stored locally). A sparse file is a much better device to use for creating a placeholder file insofar as it is non-proprietary, and this is likely why Dropbox chose to use sparse files in favor of the compressed file hack. However, not all filesystems support sparse files. CCC can only preserve these placeholder files when copying to another APFS volume. If you back up your APFS-hosted Dropbox folder to an HFS+ backup volume, the placeholder files will consume all of the space of the real file, but will contain no data (just a bunch of zeroes). While this is functionally consistent with the content of the source file (no data stored locally!), your backup will consume considerably more space than the source. This is not a limitation of CCC, this is simply a limitation of backing up APFS volumes to HFS+ volumes.

If you're using Dropbox's Smart Sync feature, we recommend excluding the Dropbox folder from your backup if your source volume is APFS formatted and the destination is not APFS formatted.

Product:

ccc5

Tags:

Advanced Topics

Filesystem implementation details

.HFS+ Private Directory Data*
/.journal
/.journal_info_block
.afpDeleted*
._*
.AppleDouble
.AppleDB
/lost+found
Network Trash Folder
.TemporaryItems

Volume-specific preferences

.metadata_never_index
.metadata_never_index_unless_rootfs
/.com.apple.timemachine.donotpresent
.VolumeIcon.icns
/System/Library/CoreServices/.disk_label*
/TheVolumeSettingsFolder

Apple-proprietary data stores

.DocumentRevisions-V100*
.Spotlight-V100
/.fseventsd
/.hotfiles.btree
/private/var/db/systemstats

Volume-specific cache files

/private/var/db/dyld/dyld_*
/System/Library/Caches/com.apple.bootstamps/*
/System/Library/Caches/com.apple.corestorage/*

NetBoot local data store

/.com.apple.NetBootX

Dynamically-generated devices

/Volumes/*
/dev/*
/automount
/Network
/.vol/*
/net

These items represent special types of folders on macOS. These should not be backed up, they are dynamically created every time you start the machine.

Quota real-time data files

/.quota.user
/.quota.group

Large datastores that are erased on startup

/private/var/vm/*
/private/tmp/*
/cores

Trash

.Trash
.Trashes

Choose Copy Some Files from the popup menu underneath the Source selector
Click the Inspector button adjacent to that same popup menu to reveal the Task Filter window
Uncheck the box next to Don't copy the Finder's Trash
Click the Done button

Time Machine backups

/Backups.backupdb
/.MobileBackups
/.MobileBackups.trash

Corrupted iCloud Local Storage

Library/Mobile Documents.*
.webtmp

Special files

/private/tmp/kacta.txt
/private/tmp/kactd.txt
/private/var/audit/*.crash_recovery
/private/var/audit/current
/Library/Caches/CrashPlan
/PGPWDE01
/PGPWDE02
/.bzvol
/.cleverfiles
/Library/Application Support/Comodo/AntiVirus/Quarantine
/private/var/spool/qmaster
$Recycle.Bin
Library/Preferences/ByHost/com.apple.loginwindow*

Default Filter Behavior

Include everything by default: Define what is excluded

Exclude everything by default: Define what is included

Calculating disk usage and Protected Size

Source and destination options

Excluded files are not deleted from the destination

Custom Filters

Anchored path filter

Subpath filter

Wildcard characters

Expert settings

Including folders and their content with the 'Exclude everything by default' filter behavior and custom rules

Exporting and Importing filters

Items automatically excluded

Related documentation

When do I need to create a Recovery HD volume?

What is the difference between archiving the Recovery HD and creating a new Recovery HD?

Why were other volumes on my disk unmounted when I created a Recovery HD?

Can I create a Recovery HD on an Apple Fusion (aka "CoreStorage") volume?

Reduce the number of files considered for backup

Related Documentation

Hard drive performance and interface bandwidth

Filesystem performance and hardware type

Spotlight Indexing

Find and replace corrupted files

Other applications and conditions that can lead to performance problems

Related Documentation

CCC will only back up system files to locally-attached macOS-formatted filesystems

Related Documentation

Ownership and permissions concerns

What can I do when there are permissions or ownership issues that prevent CCC from copying items to/from or updating items on a network volume?

Limitations of non-macOS-formatted filesystems

Support for third-party filesystems

Writable NTFS filesystems

Related Documentation

Backing up a Boot Camp installation of Windows

Backing up the contents of an NTFS volume

NAS service failures can lead to unreliable backups

Mounting the source or destination volume before a backup task begins

SafetyNet Pruning

Destination volume options

Power management options

Turn off the computer if it was previously off

Power Management options are ignored in some cases

Power Management options are applied regardless of task success

Run another backup task (task chaining)

Running shell scripts before and after the backup task

First parameter

Second parameter

Third parameter

Fourth parameter

AppleScripts are not supported

Shell scripts require a shell interpreter line

Security implications of pre and post clone shell scripts

Example pre and post clone shell scripts

How do I restore files from the _CCC SafetyNet folder?

Why can't I open some files in the _CCC SafetyNet folder?

Can I restore a previous version of the OS using one of the archives in the _CCC SafetyNet folder?

I deleted files from my startup disk to make more room, but now it's hard to find some of those files on my backup volume

Why can't I delete some items from the SafetyNet folder? The Finder says that some items are in use.

How can I prevent Migration Assistant from copying the CCC SafetyNet folder during a migration?

Default Filter Behavior

Include everything by default: Define what is excluded

Exclude everything by default: Define what is included

Calculating disk usage and Protected Size

Source and destination options

Excluded files are not deleted from the destination

Custom Filters

Anchored path filter

Subpath filter

Wildcard characters

Expert settings

Including folders and their content with the 'Exclude everything by default' filter behavior and custom rules

Exporting and Importing filters

Items automatically excluded

Related documentation

Reduce the number of files considered for backup

Related Documentation

Hard drive performance and interface bandwidth

Filesystem performance and hardware type