![]() ![]() Currently, four namespaces exist: user, trusted, security and system. The name must be a null-terminated string prefixed by a namespace identifier and a dot character. Any regular file or directory may have extended attributes consisting of a name and associated data. In Linux, the ext2, ext3, ext4, JFS, Squashfs, UBIFS, Yaffs2, ReiserFS, Reiser4, XFS, Btrfs, OrangeFS, Lustre, OCFS2 1.6, ZFS, and F2FS filesystems support extended attributes (abbreviated xattr) when enabled in the kernel configuration. The system namespace is primarily used by the kernel for access control lists and mandatory access control. The user namespace has no restrictions with regard to naming or contents. Currently, two namespaces exist: user and system. The name must be a null-terminated string, and exists in a namespace identified by a small-integer namespace identifier. Each attribute consists of a name and the associated data. Any regular file may have a list of extended attributes. In FreeBSD 5.0 and later, the UFS1, UFS2, and ZFS filesystems support extended attributes, using the extattr_ family of system calls. Extended file attributes can be viewed and edited in Be-like systems' GUI through the file-manager, often Tracker or derivatives thereof. The uses of extended attributes in Be-like systems are varied: For example, Tracker and OpenTracker, the file-managers of BeOS and Haiku respectively, both store the locations of file icons in attributes, Haiku's "Mail" service stores all message content and metadata in extended file attributes, and the MIME types of files are stored in their attributes. The Be File System allows the indexing and querying of attributes, essentially giving the filesystem database-like characteristics. In the now-defunct BeOS and successors like Haiku, extended file attributes are widely used in base and third-party programs. ![]() ![]() The getea, setea, listea, statea, and removeea APIs support fetching, setting, listing, getting information about, and removing extended attributes. In AIX, the JFS2 v2 filesystem supports extended attributes, which are accessible using the getea command. In Unix-like systems, extended attributes are usually abbreviated as xattr. Typical uses include storing the author of a document, the character encoding of a plain-text document, or a checksum, cryptographic hash or digital certificate, and discretionary access control information. Unlike forks, which can usually be as large as the maximum file size, extended attributes are usually limited in size to a value significantly smaller than the maximum file size. Extended file attributes are file system features that enable users to associate computer files with metadata not interpreted by the filesystem, whereas regular attributes have a purpose strictly defined by the filesystem (such as permissions or records of creation and modification times). ![]()
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