On Fri, Oct 07, 2016 at 02:19:53PM +0000, Jäkel, Guido wrote: > >-----Original Message----- > >From: lxc-users [mailto:lxc-users-boun...@lists.linuxcontainers.org] On > >Behalf Of Stéphane Graber > >Sent: Friday, October 07, 2016 3:38 PM > >To: LXC users mailing-list > >Subject: Re: [lxc-users] Establish a bind mount to a running container > > > >On Fri, Oct 07, 2016 at 01:26:26PM +0000, Jäkel, Guido wrote: > >> >-----Original Message----- > >> >From: lxc-users [mailto:lxc-users-boun...@lists.linuxcontainers.org] On > >> >Behalf Of Stéphane Graber > >> >Sent: Friday, October 07, 2016 11:46 AM > >> >To: LXC users mailing-list > >> >Subject: Re: [lxc-users] Establish a bind mount to a running container > >> > > >> >On Fri, Oct 07, 2016 at 07:03:21AM +0000, Jäkel, Guido wrote: > >> >> Dear experts, > >> >> > >> >> I wonder if it's possible to establish a bind mount filesystem resource > >> >> from the LXC host to an already running > >container in > >> >an manual way, but analogous as it is done at startup time. > >> >> > >> >> I already figured out that the releasing an existing link is no thing; > >> >> just umount it from inside the container. But is > >there a > >> >way to establish one while shifting the destination of a bind mount into > >> >the right namespace? > >> >> > >> >> I ask about, because in a couple of days I have to change a (NFS) > >> >> filesystem source (because of an hardware migration) > >> >that is common to a large number of running containers but not frequently > >> >used and I want to avoid to restart all the > >> >containers with it services. > >> >> > >> >> thank you for advice > >> >> > >> >> Guido > >> > > >> >It's very difficult due to a number of restrictions in place in the > >> >kernel. > >> > > >> >The only way of doing this that I'm aware of is what we do in LXD. We > >> >create a path on the host before the container starts, put that on a > >> >rshared mountpoint, then bind-mount that directory into the container > >> >under some arbitrary path. > >> > > >> >Then when you want to inject a new mount in the container, you can mount > >> >it in a sub-directory of that path you create on the host, which will > >> >then have the container inherit the mount entry thanks to the host > >> >mountpoint being rshared and the container's mountpoint being rslave. > >> > > >> >Once the mountpoint shows up in the container, you can then move it to > >> >whatever path you actually want it on. > >> > >> > >> Dear Stéphane, > >> > >> I sorry, but I don't get it yet; some of your terms and where to do it are > >> dubious to me. Maybe an example may light it up > >to me: > >> > >> Let say, I want to inject the path > >> host:/mnt/some_host_mountpoint/some_directory as a bind mount to a running > >container; it should end up on container:/import/some_container_moutpoint > >. On the host, the mountpoint > >host:/mnt/some_host_mountpoint is mouted to a NFS source, let say > >nfshost:/some_export > >> > >> Now please, where to issue which commands? > > > >You'll have to do some research yourself or hope that someone can give > >you step by step instructions :) > > > > > >A guestimate (completely untested) would be: > > > >Setup steps, before you first start the container: > > > > 1) mkdir /tmp/shared-c1 > > 2) mount --bind /tmp/shared-c1 /tmp/shared-c1 > > 3) mount --make-rshared /tmp/shared-c1 > > 4) Add to /var/lib/lxc/c1/config => lxc.mount.entry=/tmp/shared-c1 /.shared > > none bind,create=dir 0 0 > > 5) lxc-start -n c1 > > > >At which point, you could inject a new mount with: > > > > 1) mkdir /tmp/share-c1/some_directory > > 2) mount -- bind /mnt/some_host_mountpoint/some_directory > > /tmp/share-c1/some_directory > > 3) lxc-attach -n c1 -- mkdir -p /import/some_container_mountpoint > > 4) lxc-attach -n c1 -- mount --move /.shared/some_directory > > /import/some_container_mountpoint > > > > > >Again, that's a very rough approximation from what I remember the LXD > >code is doing (though we're doing it in a mix of Go and C). > > > Thanks again. I don't read through it but the first thing I read: "Steps to > to before first start of the container". Does that mean, that there's no > chance in my case, because all the containers are already running? > > Or may I (miss)use an established bind mount (or even the rootfs mount) to > create the path /tmp/shared "here" at it's source path on the host , then > "over-bind-mount-and-rshared" it on the host and then continue the injection?
If you're lucky enough that one of your established bind-mounts is rshared, then you could. But given that it's not the default, your chances are pretty slim. It's easy enough to try though, just create a directory on the host side of your existing bind-mount, bind-mount the filesystem you want over that and see if you can see it in the container. -- Stéphane Graber Ubuntu developer http://www.ubuntu.com
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