A major feature of the way objects are protected in Coda is the use of Access Control Lists on directories.
An Access Control List, or ACL, is attached to each directory in Coda, and determines to a considerable extent who can do what in that directory. You cannot attach a Coda ACL to a file, unlike DFS ACLs. Each item in an ACL gives or takes away some permission to or from a Coda user or group. As we shall see, the effect of a directory ACL is modified slightly by the mode bits on files in that directory.
Because the ACL on a directory has much more influence on its contents than Unix directory modes have ordinarily, Coda does not allow you to make a hard link in one directory to a file in another directory. This occasionally may cause problems when you extract tar files inside Coda, or when some Makefile assumes you can create hard links between files in different directories.
Coda ACLs are not the same as Posix ACLs. Also, some Unix programs may have problems on a Coda client if they make 'illegitimate' use of mode bits instead of calling access() to determine what they are able to do.