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@@ -7,20 +7,25 @@
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Kernel Requirements
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===================
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+In short, Docker has the following kernel requirements:
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+
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+- Linux version 3.8 or above.
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+
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+- Compiled with `AUFS support <http://aufs.sourceforge.net/>`_.
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+
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+- Cgroups and namespaces must be enabled.
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+
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+
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The officially supported kernel is the one recommended by the
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:ref:`ubuntu_linux` installation path. It is the one that most developers
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will use, and the one that receives the most attention from the core
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contributors. If you decide to go with a different kernel and hit a bug,
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please try to reproduce it with the official kernels first.
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-If for some reason you cannot or do not want to use the "official" kernels,
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+If you cannot or do not want to use the "official" kernels,
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here is some technical background about the features (both optional and
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mandatory) that docker needs to run successfully.
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-In short, you need kernel version 3.8 (or above), compiled to include
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-`AUFS support <http://aufs.sourceforge.net/>`_. Of course, you need to
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-enable cgroups and namespaces.
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-
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Namespaces and Cgroups
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----------------------
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@@ -38,30 +43,11 @@ Kernels 2.6.38, and every version since 3.2, have been deployed successfully
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to run containerized production workloads. Feature-wise, there is no huge
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improvement between 2.6.38 and up to 3.6 (as far as docker is concerned!).
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-Starting with version 3.7, the kernel has basic support for
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-`Checkpoint/Restore In Userspace <http://criu.org/>`_, which is not used by
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-docker at this point, but allows to suspend the state of a container to
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-disk and resume it later.
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-
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-Version 3.8 provides improvements in stability, which are deemed necessary
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-for the operation of docker. Versions 3.2 to 3.5 have been shown to
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-exhibit a reproducible bug (for more details, see issue
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-`#407 <https://github.com/dotcloud/docker/issues/407>`_).
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-
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-Version 3.8 also brings better support for the
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-`setns() syscall <http://lwn.net/Articles/531381/>`_ -- but this should not
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-be a concern since docker does not leverage on this feature for now.
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-
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-If you want a technical overview about those concepts, you might
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-want to check those articles on dotCloud's blog:
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-`about namespaces <http://blog.dotcloud.com/under-the-hood-linux-kernels-on-dotcloud-part>`_
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-and `about cgroups <http://blog.dotcloud.com/kernel-secrets-from-the-paas-garage-part-24-c>`_.
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-
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Important Note About Pre-3.8 Kernels
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------------------------------------
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-As mentioned above, kernels before 3.8 are not stable when used with docker.
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+Kernel versions 3.2 to 3.5 are not stable when used with docker.
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In some circumstances, you will experience kernel "oopses", or even crashes.
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The symptoms include:
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@@ -126,28 +112,3 @@ distributions, is not part of the standard kernel. This means that if
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you decide to roll your own kernel, you will have to patch your
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kernel tree to add AUFS. The process is documented on
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`AUFS webpage <http://aufs.sourceforge.net/>`_.
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-
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-Note: the AUFS patch is fairly intrusive, but for the record, people have
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-successfully applied GRSEC and AUFS together, to obtain hardened production
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-kernels.
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-
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-If you want more information about that topic, there is an
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-`article about AUFS on dotCloud's blog
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-<http://blog.dotcloud.com/kernel-secrets-from-the-paas-garage-part-34-a>`_.
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-
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-
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-BTRFS, ZFS, OverlayFS...
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-------------------------
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-
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-There is ongoing development on docker, to implement support for
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-`BTRFS <http://en.wikipedia.org/wiki/Btrfs>`_
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-(see github issue `#443 <https://github.com/dotcloud/docker/issues/443>`_).
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-
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-People have also showed interest for `ZFS <http://en.wikipedia.org/wiki/ZFS>`_
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-(using e.g. `ZFS-on-Linux <http://zfsonlinux.org/>`_) and OverlayFS.
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-The latter is functionally close to AUFS, and it might end up being included
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-in the stock kernel; so it's a strong candidate!
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-
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-Would you like to `contribute
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-<https://github.com/dotcloud/docker/blob/master/CONTRIBUTING.md>`_
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-support for your favorite filesystem?
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Solomon Hykes