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.. _hardware-enablement-kernels:
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=================================
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Using hardware-enablement kernels
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=================================
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As of MAAS 1.9 this feature is configured by setting the hwe_kernel variable
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instead of the architecture variable.
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MAAS allows you to use hardware enablement kernels when booting nodes
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with Ubuntu that require them.
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What are hardware-enablement kernels?
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-------------------------------------
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Brand new hardware gets released all the time. We want that hardware to
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work well with Ubuntu and MAAS, even if it was released after the latest
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release of MAAS or Ubuntu. Hardware Enablement (HWE) is all about keeping
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pace with the new hardware.
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Ubuntu's solution to this is to offer newer kernels for older releases.
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There are at least two kernels on offer for Ubuntu releases: the
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"generic" kernel -- i.e. the kernel released with the current series --
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and the Hardware Enablement kernel, which is the most recent kernel
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There are separate HWE kernels for each release of Ubuntu, referred to
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as ``hwe-<release letter>``. So, the 14.04 / Trusty Tahr HWE kernel is
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called ``hwe-t``, the 12.10 / Quantal Quetzal HWE kernel is called
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``hwe-q`` and so on. This allows you to use newer kernels with older
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releases, for example running Precise with a Saucy (hwe-s) kernel.
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For more information see the `LTS Enablement Stack`_ page on the Ubuntu
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.. _LTS Enablement Stack:
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https://wiki.ubuntu.com/Kernel/LTSEnablementStack
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Booting hardware-enablement kernels
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-----------------------------------
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MAAS imports hardware-enablement kernels along with its generic boot
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images. These hardware-enablement kernels are specified by using min_hwe_kernel
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or hwe_kernel variables.
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The min_hwe_kernel variable is used to instruct MAAS to ensure the release to
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be deployed uses a kernel version at or above the value of min_hwe_kernel. For
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example if min_hwe_kernel is set to hwe-t when deploying any release before
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Trusty the hwe-t kernel will be used. For any release after Trusty the default
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kernel for that release will be used. If hwe-t or newer is not availible for
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the specified release MAAS will not allow that release to be deployed and throw
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min_hwe_kernel can be set by running the command::
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$ maas <profile-name> node update <system-id>
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min_hwe_kernel=hwe-<release letter>
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It's also possible to set the min_hwe_kernel from the MAAS web UI, by visiting
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the Node's page and clicking ``Edit node``. Under the Minimum Kernel field, you
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will be able to select any HWE kernels that have been imported onto that node's
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.. image:: media/min_hwe_kernel.png
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You can also set the hwe_kernel during deployment. MAAS checks that the
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specified kernel is avalible for the release specified before deploying the
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node. You can set the hwe_kernel when deploying by using the command::
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$ maas <profile-name> node start <system-id> distro_series=<distro>
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hwe_kernel=hwe-<release letter>
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Or through the web interface as seen below.
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.. image:: media/hwe_kernel.png