[Lxc-users] read only rootfs

[Michael H. Warfield]

On Tue, 2011-07-19 at 15:32 -0500, Serge E. Hallyn wrote: 
> Quoting Michael H. Warfield (mhw at WittsEnd.com):
> > On Tue, 2011-07-19 at 13:34 -0500, Serge E. Hallyn wrote: 
> > > Quoting C Anthony Risinger (anthony at xtfx.me):
> > > > there it would seem.  however, while i could *maybe* see the rootfs
> > > > being an unconditional slave, i would NOT want to see any lxc
> > > > default/enforcement preventing container -> host propagation on a
> > > > globally recursive scale.  im of the opinion that the implementor
> > > > should decide the best tactic ... especially in light of the fact the
> > > > one distro may not even have the same problems as say
> > > > ubutnu/fedora/etc because they keep mount points private by default.
> > 
> > > Good point.  (I don't see it on ubuntu either fwiw)  Perhaps there
> > > should be a toggle in the per-container config file?
> > 
> > Quick question.
> > 
> > Is there any way to test for these flags (SHARED, PRIVATE, SLAVE)?  I
> > don't see them showing up anywhere from mount, in proc mounts or
> > mountstats.  How do you check to see if they are set?

> /proc/self/mountinfo is supposed to tell that.  i.e. if you do
> a --make-shared on /mnt, it'll show 'shared' next to the /mnt entry.
> (I say 'is supposed to' bc --make-rslave just shows nothing, but
> maybe that's bc the way i did it it wasn't a slave to anything,
> so it was actually private)

Ok...  This just gets weirder.

For giggles, I set my /srv partition (where all my VM's are located) to
"shared".  Now. the first machine starts up fine but the second one,
Plover, and all subsequent ones blow up with this:

[root at forest ~]# lxc-start --name Plover
lxc-start: Invalid argument - pivot_root syscall failed
lxc-start: failed to setup pivot root
lxc-start: failed to set rootfs for 'Plover'
lxc-start: failed to setup the container
lxc-start: invalid sequence number 1. expected 2
lxc-start: failed to spawn 'Plover'
lxc-start: Device or resource busy - failed to remove cgroup '/sys/fs/cgroup/systemd/Plover'

And mount -t devpts shows ALL the devpts mounts for all the attempted
VM's.  Ok...  Guess that wasn't a good idea.

But...  I got this for the root system on Alcove.

106 55 8:17 /lxc/private/Alcove / rw,relatime master:1 - ext4 /dev/sdb1 rw,barrier=1,data=ordered

Ok...  That now says "master:1".  Not sure what it signifies...

Shut him down and changed /srv to be slave and all the containers come
up but the remount still propagates back.  Changed ran --make-rslave on
it and no influence.  Seems like we're missing a piece of the puzzle
here.

Regards,
Mike
-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
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