[Lxc-users] [Dmtcp-forum] Running DMTCP inside a LXC container

[Kapil Arya]

Hi Alexandre,

Thanks for contacting us about this issue.

We haven't tried DMTCP with LXC earlier so we can't be sure about the
situation. However, I guess you are seeing these warnings because
/proc/self/maps is listing those files with absolute paths. Can you verify
this by looking at /proc/self/maps of a process running inside the
container?

In any case, was DMTCP able to generate checkpoint images? Also, what is a
good way to figure out whether a process is running inside a container?
Also, is there a way to translate between absolute and _fake_ paths?

We might need to write a small DMTCP plugin for LXC to takes care of this.

Kapil


On Sat, Oct 5, 2013 at 4:31 PM, Alexandre Gravier <al.gravier at gmail.com>wrote:

> Hello,
>
> I'm trying to use DMTCP to save my user sessions on an online service
> that offers LXC virtual machines. The service shutdowns the container
> after 15 minutes of inactivity on my side, and I would like to be able
> to save my tmux session and all related processes to disk before that
> happens.
>
> So, I've compiled DMTCP 2.0, and 40 out of 45 tests pass*. I figured
> that I may try to do something simple first, so I launch the
> coordinator in a terminal, and `bin/dmtcp_launch cat` in another. The
> coordinator notes that "NOTE at dmtcp_coordinator.cpp:1039 in
> onConnect; REASON='worker connected'". It all seems fine, and the
> clients list contains my cat.
>
> The problem comes when I actually make a checkpoint using 'c' in the
> coordinator. The coordinator goes through what seems to be a
> reasonable list of stages, from "starting checkpoint, suspending all
> nodes" to "restarting all nodes", but in the terminal where the
> dmtcp-monitored "cat" is running, there is an avalanche of errors that
> all look like:
>
> [11795] mtcp_writeckpt.c:718 write_ckpt_to_file:
>   ERROR: error statting
>
> /var/lib/lxc/vm-524f2a6f88716f1d3800785a/overlay/home/agravier/dmtcp-2.0/plugin/ipc/libdmtcp_ipc.so
> : No such file or directory
> [11795] mtcp_writeckpt.c:718 write_ckpt_to_file:
>   ERROR: error statting
> /var/lib/lxc/rootfs/lib/x86_64-linux-gnu/ld-2.17.so : No such file or
> directory
>
> And there are dozens of those.
>
> Visibly, mtcp is looking for files using their absolute path *outside*
> of the LXC container, which, of course, does not correspond to their
> paths inside of it.
>
> I would like to understand how LXC chroots in a way that still allows
> MTCP to get hold of the original filepaths. Why does MTCP get confused
> when other applications don't? Or rather, why it doesn't get confused
> by LXC :) ?
>
> Is there is anything that I might do about all that?
>
> Thanks and regards,
> Alexandre
>
>
> * Failing tests: shared-memory (rstr), pty2, bash (rstr), script, screen.
>
>
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