BSD & Sys5 Job Control

[Guy Harris]

> In BSD, processes must be coded to properly handle job control.

In job control, programs that *want to know* about job control, or that have
sections where they don't want to be stoppable, must be changed to know
about job control.  Most UNIX utilities don't know about it.

In shell layers, programs that want to know that the terminal has been taken
away from them have no way of finding this out.  Thus, if they have to reset
some mode in the terminal (not in the terminal driver, but in the terminal
itself - e.g., turning off Tektronix mode on a VT100 with a Tektronix
emulation board) can't be told when to do so.

> Sys5's sh & korn-sh (at least ours) doesn't know about job control

That's because vanilla System V doesn't *have* job control.  "ksh" will
support job control on systems which have it.  In fact, I've seen code in
"ksh" that looks like it tries to use the shell layers kernel support to
implement something sort of like job control, if you have shell layers
kernel support but not job control.