[CRIU] CRIU with GNU Screen: dumping and restoring entire process trees under Screen

[Adrian Reber]

Many years ago ;) I also tried to migrate screen, but I gave up used
tmux instead to checkpoint and restart it. I think it was related to the
socket screen uses. But it was a long time ago. At that time it worked with
tmux and I settled for that. But I would recommend just to try it and
see if it works.

		Adrian

On Wed, Apr 29, 2020 at 07:43:14PM +0100, Nikhil Nair wrote:
> Hi Pavel,
> 
> Thanks for getting back to me.  I hadn't realised that the WSL side of this
> would be the major issue, but it makes complete sense in hindsight.  I did
> a quick Google search, and found this:
> 
> https://github.com/Microsoft/WSL/issues/2833
> 
> In short, someone tried CRIU under WSL in Jan 2018, found it didn't work
> (giving an error that /proc/<pid>/map_files wasn't found), and reported it
> to Microsoft.  I've just checked, and my current version of WSL still
> doesn't have /proc/.../map_files, so it looks like that hasn't changed
> since then.  The fact that your test came up with different errors suggests
> that there are multiple issues when trying to run CRIU under WSL, and that
> this probably won't be fixed anytime soon.
> 
> A pity.  Oh well.  So, I suppose if I want persistence across reboots on
> Windows, I'll just have to run a Linux VM, under Hyper-V/VMware/whatever.
> 
> Aside from the WSL question, though, I'm still interested in knowing how to
> checkpoint/restore an interactive screen process tree: there have been a
> number of times when I've wished I could preserve my working setup across
> server reboots.  Do I take it that, given the existence of the (empty)
> article about this, that it is completely doable?
> 
> If anyone could give me some pointers on this - or, better still, direct me
> to some instructions on how to do it - I'd appreciate it.
> 
> Thanks, and best wishes,
> 
> Nikhil.
> 
> 
> On Fri, 24 Apr 2020, Pavel Tikhomirov wrote:
> 
> > Hello Nikhil!
> > 
> > I'm not sure anyone actually checked that criu works on wsl, some
> > kernel interfaces may be not implemented.
> > 
> > I've just tried criu on WSL and got some errors:
> > 
> > 
> > :/home/snorch/devel/criu# criu check
> > Warn  (criu/kerndat.c:659): Can't load /run/criu.kdat
> > Error (criu/util.c:714): exited, status=3
> > Error (criu/util.c:714): exited, status=3
> > Error (criu/kerndat.c:47): Can't open 0/pagemap on procfs: No such
> > file or directory
> > Error (criu/sysctl.c:368): Can't open sysctl vm/mmap_min_addr: No such
> > file or directory
> > Warn  (criu/kerndat.c:137): Can't fetch vm/mmap_min_addr value, use
> > default 0x10000
> > :/home/snorch/devel/criu#
> > 
> > Best Regards, Tikhomirov Pavel.
> > 
> > ??, 17 ???. 2020 ?. ? 13:06, Nikhil Nair <nnair at pobox.com>:
> > > 
> > > Hi,
> > > 
> > > I'm completely new to CRIU, and it sounds very interesting.
> > > 
> > > On the website, I found a page about using CRIU to dump and restore entire
> > > process trees under screen, but it seems the page is empty, and has been so
> > > for 3 years.
> > > 
> > > I'm hopeful, though, that the existence of that page means this is very
> > > doable indeed.  Is that right?  I've searched the archive of this list for
> > > an answer to this, as well as Googling it, but couldn't find anything.
> > > 
> > > Ideally, I'd like to be able to have a script running in the background
> > > which will take a snapshot of my screen session (which typically has one
> > > Emacs session running within it, plus a number of bash shells with
> > > different CWDs and screen contents) every several minutes (and then delete
> > > old snapshots so that it only keeps the last few at any time).  I presume
> > > taking a snapshot will involve both a CRIU dump and taking a copy of my
> > > relevant working directories.
> > > 
> > > The reason I'm looking at this is that I'm shifting to develop on Windows
> > > 10 using their Windows Subsystem for Linux (WSL), running Ubuntu.  It's
> > > pretty much binary compatible with Ubuntu running on a normal AMD64
> > > platform with a text console (I'm not using X).
> > > 
> > > The issue is that, sometimes, the host Windows machine reboots, without
> > > always asking my permission - or, at least, only waiting so long, so if I'm
> > > away from the machine, I could come back to find the machine rebooted, and
> > > my screen session lost.  There are things I can do to make reboots less
> > > likely, but I don't trust Windows not to reboot if it considers it
> > > important, without giving me a chance to save my work.
> > > 
> > > But honestly, even if I did have a chance to save my work, taking a
> > > snapshot would be much easier than setting up the screen session from
> > > scratch, anyway.
> > > 
> > > So... what's the situation?  Is this reasonably straightforward?
> > > 
> > > If the above won't work, I could look into using lxc under WSL, and
> > > snapshot the container; but that seems overkill, for what I'm after.
> > > Docker would have been an option, but I gather (from the CRIU website) that
> > > dumping an interactive container isn't yet enabled in Docker.
> > > 
> > > Cheers,
> > > 
> > > Nikhil.
> > > _______________________________________________
> > > CRIU mailing list
> > > CRIU at openvz.org
> > > https://lists.openvz.org/mailman/listinfo/criu
> > 
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		Adrian

-- 
Adrian Reber <adrian at lisas.de>            http://lisas.de/~adrian/
Behind every great man, there is a woman -- urging him on.
		-- Harry Mudd, "I, Mudd", stardate 4513.3