Date: Wed, 19 Mar 1997 05:57:58 -0800 (PST) From: Mike Pritchard <mpp> To: jkh@time.cdrom.com (Jordan K. Hubbard) Cc: hackers@freebsd.org Subject: Re: dup3() - I've thought it over and decided... Message-ID: <199703191357.FAA22301@freefall.freebsd.org> In-Reply-To: <20682.858762363@time.cdrom.com> from "Jordan K. Hubbard" at Mar 19, 97 01:06:03 am
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Jordan K. Hubbard wrote: > > > How about going more along the checkpoint/restart route? Suspend > > the process, checkpoint it, and on restart you can reconnect stdin/out/err > > to either the current tty, or to another file. Reconnecting to > > a pipeline should also be possible. I can dig up the USENIX paper > > the Cray guys wrote on this if you like :-). > > Does the checkpoint feature allow you to complete snapshot process > state? That's another item on my wishlist. :-) > > I wouldn't mind reading that paper, if you can dig it up. The best I could do for now was come up with was the information available from www.usenix.org: Authors: Brent A. Kingsbury, John T. Kline, Cray Research Title: Job and process recovery in a UNIX-based operating system Winter 1989 USENIX However, while searching around, it looks like there is a POSIX draft floating around that has something to say on the matter of checkpoint/restart. As for Cray's implementation, yes, it allows you to create a complete snapshot of the process, process group, or session. At this point you could either kill the the proc/pgrp/session for later restart, or allow it to keep running and only use the snapshot in case of a system crash. I was involved in some work on this that allowed you to checkpoint the process on one machine and then restart it on another for load leveling purposes. It was used mainly for checkpoint/restart of long running batch jobs submitted via NQS, but it was usable with interactive jobs to a degree. There was on-going work for better interactive support when I left Cray (see below). > Anyone remember a timesharing system called ITS (from MIT)? If you > got disconnected from the modem (not uncommon in those days of > Pennywhistle, 300 baud acoustically-coupled modems :-) you wouldn't > lose your session, like you do under UNIX, rather the next time you > logged in it would ask you: > > [Attach your detached tree?] > > And if you said 'y' you'd get your old process tree back, everything > right where you left it. I used to use CDC's NOS that had this feature. Very useful. I think that Cray's current implementation also has this feature. -- Mike Pritchard mpp@FreeBSD.org "Go that way. Really fast. If something gets in your way, turn"
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