Thanks Cal. I will look into this. However, for now, I have found a quick fix. I just added "lxc.pivotdir = /mnt" to my config file. The pivotdir is used when pivoting the original root file system. It seems that in older versions of lxc, the default value was /mnt but this was changed since (in my case it was /usr/lib/x86_64-linux-gnu/ lxc/lxc_putold by default). Nothing is actually written in this directory, so it can work even in read-only mode. However, if this location does not exist lxc will try to create it, which will fail. mnt/ exists so no problem. I hope I did not break anything by changing it to /mnt. So far it seems to be working. Note that I still have the following error:
lxc-execute: Read-only file system - error unlinking /usr/lib/x86_64-linux-gnu/lxc/ dev/kmsg but it does not provide the container from spawning. Antonin 2013/12/18 Cal Leeming [Simplicity Media Ltd] <[email protected]>: > It looks like something being executed is expecting your rootfs to be > writeable, this could be something in lxc-execute or it could be /bin/bash > itself (I wouldn't know without strace'ing both or looking at the source). > > You could try adding the necessary /dev, /proc and /sys mounts, which may be > enough to get it to run without error (add the following into your lxc > config); > http://pastebin.com/ZAcXn926 > > However any applications expecting a write-able FS are going to fail hard - > for example, anything relying on /tmp, or /var/log, and numerous other > places. You could in theory bind mount a ramfs to those locations, but it > would be easier, in my opinion, to use a stacked file system. > > Here is an example of using overlayfs; > http://askubuntu.com/questions/109413/how-do-i-use-overlayfs > > In short, you'd build your container rootfs and make whatever changes you > wanted to make, once you're happy with it you then do; > > $ mount -t overlayfs -o > lowerdir=/your.rootfs.here,upperdir=/your.discarded.changes.here overlayfs > /your.new.mount.here > lxc.rootfs = /your.new.mount.here > > There is also a previous discussion on this; > http://osdir.com/ml/lxc-chroot-linux-containers/2011-07/msg00019.html > https://www.redhat.com/archives/libvirt-users/2011-December/msg00024.html > http://s3hh.wordpress.com/2011/09/22/sharing-mounts-with-a-container/ > https://www.mail-archive.com/[email protected]/msg02190.html > > Hope this helps > > Cal > > > On Thu, Dec 19, 2013 at 1:51 AM, Antonin Bas <[email protected]> wrote: >> >> Hi, >> >> I guess that could do it. But I don't understand while it would not be >> possible to have a read-only rootfs (i.e. is what I am seeing the >> expected behaviour?). >> What would the configuration look like if I decided to use overlayfs? >> Is it easy to use with lxc-execute? Because I just want to run an >> application, and I don't want to pay the overhead of >> lxc-start-ephemeral. >> >> Thanks, >> >> Antonin >> >> 2013/12/18 Cal Leeming [Simplicity Media Ltd] >> <[email protected]>: >> > Would it not be better to use a stacked file system, such as overlayfs >> > or >> > aufs, then discard the changes? >> > >> > Cal >> > >> > >> > On Thu, Dec 19, 2013 at 12:49 AM, Antonin Bas <[email protected]> >> > wrote: >> >> >> >> Hi, >> >> >> >> I am trying to run an application container with lxc-execute. I am >> >> going to run "untrusted" student codes in this container and I want >> >> the root file system to be shared with the host but read-only. I >> >> thought this would be as easy as using the following configuration >> >> file: >> >> >> >> # Container with new network withtout network devices >> >> lxc.utsname = omega >> >> lxc.network.type = empty >> >> lxc.network.flags = up >> >> >> >> lxc.rootfs = /tmp/guest/rootfs >> >> lxc.mount.entry=/ /tmp/guest/rootfs/ none ro,bind 0 0 >> >> >> >> However, when I run `sudo lxc-execute -n test -f grader.conf >> >> --logpriority=DEBUG -- /bin/bash`, I get the following message: >> >> >> >> lxc-execute: Read-only file system - error unlinking >> >> /usr/lib/x86_64-linux-gnu/lxc/dev/kmsg >> >> >> >> lxc-execute: failed to setup kmsg for 'test' >> >> lxc-execute: Read-only file system - failed to create directory >> >> '/usr/lib/x86_64-linux-gnu/lxc/lxc_putold' >> >> >> >> lxc-execute: Read-only file system - failed to create pivotdir >> >> '/usr/lib/x86_64-linux-gnu/lxc/lxc_putold' >> >> lxc-execute: failed to setup pivot root >> >> lxc-execute: failed to set rootfs for 'test' >> >> lxc-execute: failed to setup the container >> >> lxc-execute: invalid sequence number 1. expected 2 >> >> lxc-execute: failed to spawn 'test' >> >> >> >> >> >> Is it possible to have some insight on what the problem is here? >> >> I am using Ubuntu 13.10, and my lxc is the one from the official repo >> >> (1.0.0.alpha1). >> >> >> >> Thanks you in advance for your help, >> >> >> >> Antonin >> >> _______________________________________________ >> >> lxc-users mailing list >> >> [email protected] >> >> http://lists.linuxcontainers.org/listinfo/lxc-users >> > >> > >> > >> > _______________________________________________ >> > lxc-users mailing list >> > [email protected] >> > http://lists.linuxcontainers.org/listinfo/lxc-users >> _______________________________________________ >> lxc-users mailing list >> [email protected] >> http://lists.linuxcontainers.org/listinfo/lxc-users > > > > _______________________________________________ > lxc-users mailing list > [email protected] > http://lists.linuxcontainers.org/listinfo/lxc-users _______________________________________________ lxc-users mailing list [email protected] http://lists.linuxcontainers.org/listinfo/lxc-users
