lxc and consoles and unix98 ptys (and c/r)

Serge E. Hallyn serue at us.ibm.com
Tue Apr 27 15:48:55 PDT 2010

Hi Daniel,

I know you've thought the whole console situation through
a great deal - and I haven't - so plz set me straight as

liblxc supports 'lxc.pts', which tells it to mount a fresh
/dev/pts.  However, it does this very late in the container
startup, and does not appear to support either lxc.tty consoles
or the 'main' console being in that ptsns.

When I want to checkpoint and restart something which writes
to a container in a hand-built container, what I generally do
is start sshd and screen -dm in the container, ssh in,
screen -r, start my job, detach and logout, then do my
freeze/checkpoint/restart, and then i can ssh back in and
screen -r.

That's obviously less than ideal :)  I'd like to be able to
checkpoint lightweight containers by doing

	lxc-execute -n serge -- myscript
or maybe
	lxc-start -d -n serge -- myscript

and have the container init's fd 0-2 be /dev/pts/0 in the
container's devpts mount.

For that to work, lxc-execute would have to mount its new
devpts instance, then open /dev/pts/0, and start up a proxy
to ferry the console info back and forth.  I thought in the
past you'd talked about that, but I can't recall whether you
said you wanted to do it, or that you thought it was too
heavyweight :)

Have you had any such thing in mind?

The related feature of course woudl be for lxc-start with
lxc.tty=4 to first mount a new devpts instance, then run
getty on /dev/pts/[0-4] and let lxc-console attach to


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