UNIX IPC Datagram Reliability under - (nf)

[Robert Elz]

There's nothing remarkable about datagrams not being reliable under
unix.  No output is reliable.  You're not guaranteed to get an error
if the disk that you happen to be writing on developes a coughing fit
just at the time you do your write, you're not guaranteed to get
an error if the process at the other end of a pipe dies before reading
your data (though you will if its already dead when you send it),
nor will you get an error if your output to a terminal is mangled
by noise on the phone, or simply by some super-user type doing a "wall"
at the relevant time.

Why should unix datagrams do something different?
(As has been mentioned before, they would also cease to be
datagrams by the traditional definition.)

You will often get an error indication if something is wrong, but
you may not.

I do agree though that for most programs, datagrams are not an intelligent
service to use.

As to X.25, that can certainly not be considered to be reliable.
DCE's are permitted to RESET a virtual circuit as often as they
deem fit, and each RESET may cause data to be lost.  Higher level
protocols are necessary to guarantee data integrity.

Robert Elz,		decvax!mulga!kre