Retaining Zero-Length Files
The ZFS file retention feature treats zero-length files differently than other regular files.
When you retain a zero-length file, the file sets the appendonly
attribute. If you retain a file that has the appendonly
attribute set,
the file remains append-only.
You can add or remove write permissions from a retained
zero-length file or from a retained file that has the appendonly
attribute set.
If you remove all write permissions, the file becomes a
typical retained file, which sets the readonly
attribute and unsets the
appendonly
attribute. You can achieve the same result by setting
the readonly
attribute or by unsetting the appendonly
attribute.