Extended attributes

From ArchWiki

From xattr(7): "Extended attributes are name:value pairs associated permanently with files and directories". There are four extended attribute classes: security, system, trusted and user.

Warning: By default, extended attributes are not preserved by cp, rsync, and other similar programs, see #Preserving extended attributes.

Extended attributes are also used to set Capabilities.

User extended attributes

User extended attributes can be used to store arbitrary information about a file. To create one:

$ setfattr -n user.checksum -v "3baf9ebce4c664ca8d9e5f6314fb47fb" file.txt

Use getfattr to display extended attributes:

$ getfattr -e text -d file.txt
# file: file.txt

To remove an extended attribute:

$ setfattr -x user.checksum file.txt

To find files with certain extended attributes use rawhideAUR:

$ rh /path/to/dir '"XATTR_REGEX".reea'

Some other user extended attributes include:

  • user.mime_type: helps programs know mimetype and set it with less guesswork.
  • user.charset: used by the Apache httpd module mod_mime_xattr.
  • user.creator: The name of the application that created the file.

XDG also proposes a set of standardized extended attributes to be used by programs:

  • user.xdg.comment: supported by Dolphin and other file managers.
  • user.xdg.origin.url: for files downloaded from a url.
  • user.xdg.robots.index: "true" if a file is included in indexing, "false" otherwise
  • user.xdg.robots.backup: "true" if a file is included in backup, "false" otherwise
  • user.xdg.language
  • user.xdg.creator
  • user.xdg.publisher
  • user.xdg.origin.email.subject
  • user.xdg.origin.email.from
  • user.xdg.origin.email.message-id

Preserving extended attributes

Command Preserves by default?/Required flag
cp --archive/--preserve=all/--preserve=xattr
mv Yes1
tar --xattrs for creation and --xattrs-include='*' for extraction
bsdtar -p for extraction
rsync -X, --xattrs
cpio No
gzip No
pax No
syncthing by enabling syncXattrs
  1. mv silently discards extended attributes when the target file system does not support them.

To preserve extended attributes with text editors you need to configure them to truncate files on saving instead of using rename(2). [1]


File systems

All major Linux file systems including Ext4, Btrfs, ZFS, and XFS support extended attributes. The kernel allows to have extended attribute names of up to 255 bytes and values of up to 64 KiB, but Ext4 and Btrfs might impose smaller limits, requiring extended attributes to be within a "filesystem block".

NTFS uses Alternative Data Streams to store user. The mount option user_xattr or streams_interface=xattr should be used by default. However, it might not be supported if mount option streams_interface=windows is used. ntfs-3g supports mapping Alternative Data Streams to extended attributes in FUSE.

NFS does not currently support extended attributes.


Application Supported extended attributes Notes
caja Yes Supported by caja-xattr-tags and caja.eiciel extensions.
Chromium No Used to support referrer and url, but was disabled due to privacy and security concerns. See also CVE-2018-20483.
braveAUR No
Enabled with --xattrs flag.
Dropbox user.com.dropbox.attributes
emacs-vm No Resets mbox xattrs.
Epiphany No
Exiftool No
fd No
findutils No
Firefox No
gallery-dlAUR No
Gwenview user.xdg.tags
kfind No
konqueror No
kio [3]
Nautilus No
recoll user.xdg.tags
tagspacesAUR No
tmsuAUR No
Thunar No
youtube-dlAUR, yt-dlp
Enabled with --xattrs flag.
Enabled with --xattrs flag.
Webkit No

Other tagging systems

It might not be possible to use extended attributes due to lack of support of either the file system or software. For this reason, many media formats store metadata included in the file format that can be viewed using programs like Exiftool or more specified ones like id3AUR for audio.


Another filesystem-independent workaround is Gnome virtual filesystem: gvfs which is used to store metadata (gvfsd-metadata). For example, Firefox stores metadata this way and can be viewed with:

$ gio info --attributes=metadata:: downloaded.html

Other programs that use this approach include:

  • Thunar: to save file color highlights.

See also