[lxc-users] How to apply commands in howtos - macvlan and disk passthrough

Pavol Cupka pavol.cupka at gmail.com
Wed Dec 21 16:09:43 UTC 2016

these subuid mappings are there for the case that someone compromises your
container and gains root, should he break out of the container he would
have access to all the files that are root owned on the host machine, when
you use these mappings then the uses get uid + 100000 or whatever is set in
the subuid map file and if they gain root they have uid 1 in container but
uid 1000001 on the host that means it can't access any files. that is the
whole purpose of this unprivileged container thing.
yes you have to create users with corresponding uid on diff containers to
be able to access the files.

why do you have to export the same path to both containers? you can export
one path for one container and other for the second one. but your setup
will work for media/backup and for other things

On Wed, Dec 21, 2016 at 3:41 PM, John Gubert <john.gubert at web.de> wrote:

> Hi Pavol,
> thanks for the link, I did some testing with the out of the box setup
> (removed root:1000:1) of ubuntu, created two containers and passed the same
> host directory through to both of them, then I created the same users in
> the same order on both containers:
> root(1000)
> neuer(1001)
> zweiter(1002)
> this seems to work, when I create files inside this folder on one
> container as neuer, I can only read them as neuer on the other container
> and vice versa.
> I would assume, that as soon as I create the users in a different order,
> zweiter might become 1001 and neuer 1002 and therefore files created by
> neuer in one container would be seen as files created bei zweiter in the
> other, right? On the host, all files are seens as 101001 or 101001 anyway.
> I would go ahead and use this setup for my homeserver to store
> media/backups and run a fileserver in one container and other tasks in
> another, is this setup stable enough if I set it up as described above?
> this is my lxc config, is there anything I should change?
>   disktest:
>     path: /testdisk
>     source: /home/me/testdisk
>     type: disk
> kind regards,
> John
> Am 21.12.2016 um 15:04 schrieb Pavol Cupka:
> some of your questions are answered here
> https://wiki.gentoo.org/wiki/LXD#Configure_subuid.2Fsubgid
> answering to the list is fine
> On Wed, Dec 21, 2016 at 1:34 PM, John Gubert <john.gubert at web.de> wrote:
>> Hi Tycho,
>> thank you for your fast response.
>> My id on the host is indeed 1000. I read your blog article and then had
>> a look at /etc/subuid:
>> before:
>> "me at host:~$ cat /etc/subuid
>> lxd:100000:65536
>> root:100000:65536
>> me:165536:65536"
>> after:
>> "me at host:~$ cat /etc/subuid
>> lxd:100000:65536
>> root:100000:65536
>> me:165536:65536
>> root:1000:1"
>> root seems to be already set up, maybe this is due to lxd being
>> installed on ubuntu 16.04? It would be really helpful if you could
>> explain to me what the mapping defined in this file really does. Does it
>> make a difference if I add your line, or use the one already there? How
>> does this file use the numbers (100000 and 65536)? Does 1000:1 tell
>> ubuntu to map the id 1 to 1, if so, what does 100000:65536 mean? Add
>> 65536 to the 100000? If there is a user called "me" in the conatainer,
>> does a line "me:1000:1" work as well?
>> I appreciate any help.
>> with kind regards,
>> John
>> P.S.:
>> I answered to the mailing list, is this the right way to do it, or
>> should I answer to you directly?
>> Am 20.12.2016 um 22:52 schrieb Tycho Andersen:
>>> Hi John,
>>> On Tue, Dec 20, 2016 at 10:39:07PM +0100, <john.gubert at web.de>
>>> john.gubert at web.de wrote:
>>>>     Hello,
>>>>          I have a directory on my host system and want to create
>>>> several containers
>>>>     with the same users inside. I would like to pass the directory
>>>> through to
>>>>     each container and allow the users to write and read on it. The
>>>> network
>>>>     connection should be done using macvlan.
>>>>     The howtos I have read so far show how to set up lxd, which works
>>>> very
>>>>     well on my 16.04 host. Starting a container works out of the box as
>>>>     unpriviliged user as well.
>>>>          My questions:
>>>>     Is it even possible to share one directory on the host with several
>>>>     container?
>>>>     All the howtos I could find mention some commands, that need to be
>>>>     applied, but they do not tell me about the commands I need to type
>>>> in to
>>>>     make it work:
>>>>     "That means you can create a container with the following
>>>> configuration:
>>>>     lxc.id_map = u 0 100000 65536
>>>>   lxc.id_map = g 0 100000 65536"
>>>>     There is a big list of possible options on github, but where does
>>>> it tell
>>>>     how to apply them?
>>>>          Does someone know a detailed howto, that describes a similiar
>>>> setup like
>>>>     mine?
>>> http://tycho.ws/blog/2016/12/uidmap.html is a blog post I wrote a
>>> while ago talking about how to set this up with your home directory.
>>> You can mimic the settings for whatever user map you want, though.
>>> Cheers,
>>> Tycho
>>>     Every time I read something, I feel like missing something important,
>>>>     because I could not find a coherent compendium of possible options
>>>> on how
>>>>     to do something.
>>>>          kind regards,
>>>>     John
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