NFS is an important exception, and files copied to NFS will have all their xattrs stripped. Most file systems to which macOS can write either handle xattrs natively (HFS+, APFS), or macOS uses a scheme to preserve them. These should be pathological problems, but could also result from malicious activity. It’s possible to fill a volume with extended attributes and run it out of free space, and that space may also be ignored by services which manage storage use, for example space allocations for clients in a server system. Each file and folder can have an effectively unlimited number of xattrs, each of which can be more than 100 KB.īecause they’re part of the volume metadata, some versions of macOS may not include the space occupied by them when calculating free and used disk space. As such they’re out of reach of normal file tools, and can only be accessed using those specifically intended to work with xattrs. In Mac native file systems such as APFS, extended attributes aren’t stored with the main data for files, but in the Attributes area of the volume metadata. They’re not normally used to store content-specific metadata such as EXIF for images, or those associated with other media files, which are normally incorporated within the file data to ensure their preservation on all file systems. Other xattrs might attach details of the website from which a file was downloaded, copyright information, and more. One of the most prominent is implementing the quarantine flag which indicates that a file has been downloaded from the internet and requires full security checks. MacOS and applications use xattrs for various purposes. Although sometimes claimed to be a quirk of Macs, extended attributes are now quite widely used in other file systems, in Linux and BSD, for example. In macOS 10 and 11, files and folders can also have other named forks, which are implemented as extended attributes a resource fork becomes resource metadata in a xattr of type. In Classic Mac OS, many files have resource forks to contain structured metadata: a classic app, for example, stores definitions of windows, menus, dialogs, etc., in its resource fork. Extended attributes, or xattrs, are metadata which apply only to specific files, and aren’t used by the great majority: they’re options used for particular purposes. When processing very large numbers of files, however, this can become quite time-intensive and you may wish to switch this feature off during such operations.The attributes of a file include metadata which is common to many or all files, such as their name and date of creation. We suggest that you keep this feature switched on in normal use. This is why by default A Better Finder Attributes sends a “please update your information on this file that I have changed” request to the Finder. This can happen quite a lot when using A Better Finder Attributes because you explicitly change file information that is susceptible to this problem. It can be very confusing when the Finder information and the actual file system are out of sync. Over time the Finder has become much more robust in detecting and displaying changes quickly, but it’s still far from perfect. The type of information that is cached by the Finder includes file names, modification and creation dates, icons, etc. In other words, the files have changed but the Finder still displays the old information. ![]() Unfortunately the Finder is not always very good at picking up changes on the file system and consequently can on occasion show “old” or “stale” information. ![]() The Mac OS X Finder keeps much of its information about the files that it displays in a fast-access cache thus allowing it to “feel quicker” because it no longer needs to access the hard disk each time it displays a file.
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