[lxc-devel] [RFC] Systemd, lxc-console, and ttys!

[Michael H. Warfield]

All,

Over on the -users list (if you haven't been tuned into the thread on
creating a Fedora container) we've been boiling out another systemd
gotcha.

Basically, lxc-console does not work with systemd because systemd does
not start containers on /dev/ttyN.  Their documentation indicates that
it's because it's in a container.  Someone has uncovered the logic
(magic cookie) that contradicts that.  The logic switch is on the
existence of /dev/tty0 (the magic cookie).  If it exists, systemd will
start gettys on /dev/ttyN (only /dev/tty1 by default) and lxc-console
will work.  If it doesn't exist, systemd will not start gettys for the
vtys and lxc-console will not work.

Obvious solution...  Create /dev/tty0 and lxc-console will work.
Looking at the code, it looks like it's rife with side effects guarded
by gremlins there in conf.c.  We would need to modify "lxc_create_tty"
and "setup_tty" in conf.c to make them 0 based, instead of 1 based, and
adjust for an additional tty (lxc.tty + 1).  That SHOULD be straight
forward.  But...  Shifting the base of the lxc_tty_info structure could
have unforeseen (on my part) side effects which could impact LOTS of
things.

Maybe it would be easier to "hack it" and create something entirely
separate to just create the special case of /dev/tty0.  I don't know.

So that's what we have to do (AFAICT) to make lxc-console play nicey
nicey with systemd and that's what it appears (to me) that we need to do
it.  But it appears that "here there be dragons".  I can do some of the
coding but I need to understand some of the implications before I make
things fall down go boom.

Regards,
Mike
-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
 PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!
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