Describes what extended attributes are, and the POSIX permissions that you need to manage them.
Extended attributes (referred to as xattrs) allow user applications to
associate additional metadata with a regular file or directory. Unlike system-level inode
metadata, such as file permissions or modification time, extended attributes are not
interpreted by the system but are instead used by applications to store additional information
about an inode. Multiple extended attributes can be associated with a single inode. The
maximum size allowed for an extended attribute is 64 KB.
An extended attribute is a name-value pair, with a string name and binary value. The extended
attribute names are prefixed with a namespace. For example, an xattr named
myXattr in the user namespace would be specified as
user.myXattr.
| Namespace | HPE Ezmeral Data Fabric Functionality |
|---|---|
| user | Commonly used by client applications. Access to these extended attributes in the user namespace is controlled by corresponding file/directory permissions. For more information, see Permissions for Extended Attributes. |
| trusted | Available to superusers only. Access is denied for all other users. The extended attribute is not available through userspace methods. |
cp -px and distcp
-px will work on extended attributes only in the following cases: hadoop fs.The following table lists the permissions (POSIX mode bits or Access Control Expression (ACE)s) you will need to set, retrieve, or modify extended attributes.
| To... | For directories, you need... | For files, you need... |
|---|---|---|
| Set extended attributes | Mode bits: write (OR)ACE: addchild |
Mode bits: write (OR)ACE: writefile |
| Remove extended attributes | Mode bits: write (OR)ACE: deletechild |
Mode bits: write (OR)ACE: writefile |
| Retrieve extended attributes | Mode bits: read (OR) ACE: readdir |
Mode bits: read (OR) ACE: readfile |