# Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

`XATTR_ROOT` (int)
  Set attribute in root (trusted) namespace. Requires root privileges.
`XATTR_DONTFOLLOW` (int)
  Do not follow the symbolic link but operate on symbolic link itself.
`XATTR_CREATE` (int)
  Function will fail if extended attribute already exists.
`XATTR_REPLACE` (int)
  Function will fail if extended attribute doesn't exist.