mullen@NRL-CSS.ARPA@sri-unix.UUCP (06/13/84)
From: Preston Mullen <mullen@NRL-CSS.ARPA> I keep seeing hints that System V (perhaps only release 2?) has some form of job control. Could someone elaborate on this and compare it with 4.2bsd job control? I am especially interested in job control at the user command (shell) level, not capabilities that are only implemented in system calls. (end of message)
gwyn@BRL-VLD.ARPA (06/17/84)
From: Doug Gwyn (VLD/VMB) <gwyn@BRL-VLD.ARPA> UNIX System V Release 2 provides a form of job control, but it differs significantly from Berkeley's: - Uses "sxt" pseudo-devices (like pty's but better) - Obtained by running "shl" (shell layers) program - Layers are transparent to applications - No signals are involved - Apparently applications cannot determine the "shl" activity (so that for example a screen editor will not be able to automatically refresh the display when the editor job is reactivated) Not available on the PDP-11/70, according to the SRD.
jab@uokvax.UUCP (06/19/84)
#R:sri-arpa:-82700:uokvax:6100034:004:1637 uokvax!jab Jun 18 19:43:00 1984 /***** uokvax:net.unix / sri-arpa!ARPA / 10:11 pm Jun 14, 1984 */ From: Preston Mullen <mullen@NRL-CSS.ARPA> I keep seeing hints that System V (perhaps only release 2?) has some form of job control. Could someone elaborate on this and compare it with 4.2bsd job control? I am especially interested in job control at the user command (shell) level, not capabilities that are only implemented in system calls. /* ---------- */ I'll tell you about it, with a quick disclaimer: I'll provide you with facts (not a rave about how good it is, or a flame about how bad it is) and let you for your own opinions. System V Release 2.0 has a utility called "shell layers", named after the "layers" program that runs on the Teletype 5620 terminal and implements windows on the dot-mapped-display screen. "shell layers" is best thought of as a "virtual terminal" facility, although it isn't as complete as the Purdue "pseudo-tty" driver. You are given the ability to run up to seven virtual terminals (each with its own /dev entry), and switch between them via a magic character, which is usually ^Z. For example, % shl >>> create layer1 layer1 (PS1 is set to the layer name) layer1 ls (output from ls) layer1 ^Z >>> create layer2 layer2 cd / layer2 ^Z >>> resume layer1 (resuming layer1) layer1 You get the gist. The magic differences from the "job control" you see now is that ^Z takes you to a "manager", not to a shell, and that the programs in each "virtual terminal" don't know that they're running in a layer. Let's not get into a discussion on whether this is a good or bad implementation. Jeff Bowles Lisle, IL