[Attribute] User append-only [chflags flag] uappnd, uappend [Owner-settable] Yes [OS support] All [Semantics and rationale] Existing data in the file can't be overwritten and the file cannot be truncated [ls flag] 
uappnd
a r c h
o p a q u e
n o d u m p
s a p p n d
s c h g
u a p p n d
u c h g
h i d d e n