what is the 'l' permission?

[Guy Harris]

>Can someone explain "mandatory locking" as used here.  I find that Sys V.3
>allows two processes to open and write to a file with 'l' permisssions.

As it is supposed to.  "Mandatory locking" merely means that if you use
"fcntl" or "lockf" to lock a region of the file, attempts to write the
locked region of the file will block until the lock is released, and
if the lock is also supposed to block attempts to read that region, it
will do that as well.