xattr: com.apple.metadata:com_apple_backup_excludeItem, exclude from backups

Type: com.apple.metadata
Subtypes: com_apple_backup_excludeItem
Serialisation: none
Data type: binary property list usually containing com.apple.backupd as a single NSString.
Example: <62706c69 73743030 5f101163 6f6d2e61 70706c65 2e626163 6b757064 08000000 00000001 01000000 00000000 01000000 00000000 00000000 00000000 1c> «bplist00_ com.apple.backupd »
macOS: Sierra, High Sierra
System use: only for /private/var/db/CoreDuet and com.apple.AssetCacheLocatorService/diskCache.plist in /private/var/folders/
App use: none
Document use: some items within iMovie Library, iTunes docs, iPhoto Library, Aperture Library, and Photos Library
Other usage: extensively in ~/Library, especially for session docs and caches

Purpose: effectively adds the item (folder and contents, or file) to Time Machine’s exclude list
Information:
Used in specific locations to ensure that files and the contents of designated folders are not backed up by Time Machine.

I don’t know whether this is respected or used by other backup software.

Could possibly be used by user to prevent backup, but the binary flags would need to be deciphered before this became reliable. The first section appears identical in each use:
<62706c69 73743030 5f101163 6f6d2e61 70706c65 2e626163 6b757064>
and the remaining content is almost always
<08000000 00000001 01000000 00000000 01000000 00000000 00000000 00000000 1c>

Rarely, may just be
<636f6d2e 6170706c 652e4d6f 62696c65 4261636b 7570> «com.apple.MobileBackup»
which may exclude from Mobile Time Machine rather than regular backups.

In High Sierra, Apple has warned users not to use Time Machine to back up Photos Libraries on external drives. Could this be related?

Tools: xattred, xattr

Links:

Original page: 2017-12-12
Last modified: 2017-12-30

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1

jaydisc on December 13, 2017 at 9:31 am

> In High Sierra, Apple has warned users not to use Time Machine to back uo Photos Libraries on external drives.

Any more information on that? Any idea why?

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- 2
  
  hoakley on December 13, 2017 at 9:43 am
  
  This is a chance observation from the Help book for Photos in High Sierra, shown here.
  Apple has introduced this advice with High Sierra, and it appears mystifying to me. Given that backups run as root and regularly back up files and folders with all sorts of permissions, it makes no sense.
  I’m wondering if Apple is using ‘permissions’ as a euphemism for xattrs, and the problem is with the xattrs which block some parts of a library from being backed up. But that’s speculation.
  Howard.
  
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  - 3
    
    jaydisc on December 13, 2017 at 9:48 am
    
    Wow. Fascinating. I wonder if it’s related to hard links? When users upgraded from Aperture/iPhoto to Photos, it used hard links to preserve the old library and have the new library without doubling the user’s storage needs. Time Machine similarly depends on hard links. Maybe there’s some connection there. Mystifying indeed.
    
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    - 4
      
      hoakley on December 13, 2017 at 9:54 am
      
      Well, if they were directory links that could cause a problem with APFS. But that would also apply to internal storage. As an external drive is more likely to be a hard disk, it is less likely to be using APFS than the internal drive.
      And this is not mentioned in the Help files for Photos in Sierra, suggesting that the problem is somehow new, i.e. something that High Sierra’s Photos does, but earlier versions didn’t.
      If only Apple could be bothered to document properly.
      Howard.
      
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Week 50 – 2017 – This Week In 4n6 on December 17, 2017 at 1:26 am

[…] xattr: com.apple.metadata:com_apple_backup_excludeItem, exclude from backups […]

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