[Lxc-users] How to make a container init DIE after finishing runlevel 0

[Tony Risinger]

hello,

over the past several weeks i have been working intensively on setting
up my personal servers with LXC based containers.  at this point, i am
extremely pleased with my setup, and will soon be sharing all that i
have accomplished in the form of several scripts and implemented
configuration ideas.  i am using LXC in conjunction with BTRFS; all of
my containers are populated inside BTRFS subvolumes/snapshots, and i
have to say this is _very_ slick.  i can create several containers in
a matter of seconds, all sharing the base install (COW of course).
this allows me to create a "nano" template, fork it at the filesystem
level, update it to a "base" template via a package manager, and
repeat this as many times as i wish (LAMP/etc).  i then fork an
appropriate template into a usable domain, again at the FS level, and
run an LXC container inside it.

anyways, that is all working extremely well, all my build/run/manage
scripts are complete.  i am however experiencing one nuisance that
works against the elegance of it all... how to convince init to die
once it enters runlevel 0 and all other processes are dead.

i swear i have tried/considered about everything... playing with
/etc/powersave, /etc/initscript, powerfail/SIGPWR, replacing
/sbin/init with /bin/true and calling init U, named pipes from host to
container/read only bind mounts of a folder with a named pipe to
trigger something in the host, kill -9 1 in inittab itself, writing a
custom init in bash, maybe using something other than init like
upstart (?), and probably several other things that i've forgotten....
 but they all feel kludgey and complicated.

init simply refuses to die unless its issued a SIGKILL from the host.
and thats super inconvenient :-(.  i know pid 1 has special properties
but i hoped there would be a nice way to address the fact that its not
_really_ pid one... it just thinks it is.

this is what i have for an /etc/inittab right now in the containers,
mostly pretty good i think:

id:3:initdefault:
rc::sysinit:/etc/rc.sysinit
rs:S1:wait:/etc/rc.single
rm:2345:wait:/etc/rc.multi
rh:06:wait:/etc/rc.shutdown
su:S:wait:/sbin/sulogin -p
c1:2345:respawn:/sbin/agetty -n -l /bin/autologin -8 38400 tty1 linux
rb:6:once:/sbin/init 3
kl:0:once:/bin/touch /dev/hostctl
p6::ctrlaltdel:/sbin/init 6
p0::powerfail:/sbin/init 0

this lets me reboot the container from the inside correctly, or from
the host with a SIGPWR, or "shutdown" with a SIGINT from the host.
the autologin binary lets the host login as root no matter what.  this
next line is my latest/final attempt at managing these "zombie"
containers once they enter runlevel 0:

kl:0:once:/bin/touch /dev/hostctl

on the host i basically run a "timeout 5m cat
/vps/dom/<DOM>/rootfs/dev/hostctl" for each dom, and monitor the
return code from that process.  the cat command will block until
"touched" by init at the end of its life.  at that point i mercilessly
SIGKILL the container init.  the other option i'm considering is a
cronjob that loops thru "running" containers, does an lxc-ps on them,
and if only one process is running assume its init and SIGKILL the
pesky bugger, this is probably the easier way.

apologies for the length, but how is everyone else handling this?
this is the last thing i need to solve before i actually start running
all my services on this setup.

thanks