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= Kernel issues =

== LTS enabled stacks: Updating the kernel in LTS versions of Ubuntu ==

{{{
sudo apt-get install --install-recommends linux-generic-hwe-16.04 xserver-xorg-hwe-16.04 
}}}

See [[https://wiki.ubuntu.com/Kernel/LTSEnablementStack#Ubuntu_16.04_LTS_-_Xenial_Xerus|this page for a description of LTS enabled stacks]]. 

== Modules included in kernel ==
To search for specific modules in the kernel, for example, to look for the wifi drivers that are included, use
{{{
modinfo iwlwifi
}}}

== Removing old kernels ==

Newer and simpler instructions here:
[[ https://help.ubuntu.com/community/RemoveOldKernels ]]

Use:
{{{
   $ sudo apt-get autoremove --purge 
}}}

Older info below:

[[ https://help.ubuntu.com/community/RemoveOldKernels#Safely_Removing_Old_Kernels]]

For users of LVM systems, encrypted systems or limited-storage systems, the most frequent problem is that the /boot partition is simply full. The package manager cannot install a pending upgrade due to lack of space. Addiitionally, apt-get can not remove a package due to broken dependency.

This problem can be fixed from the shell: by manually remvoing one or two old kernels, we can provide the package manager enough space to install the queued upgrade.

First remove any leftover temporary files from previous kernel updates.

{{{
  $ sudo rm -rv ${TMPDIR:-/var/tmp}/mkinitramfs-*
}}}

Determine the version number of the currently running kernel, which you DO NOT want to remove.

{{{
  $ uname -r
  4.2.0-21-generic
}}}

List all the kernels, including the booted one (4.2.0-21-generic in this example), in the package database and their statuses.

{{{
$ dpkg -l | tail -n +6 | grep -E 'linux-image-[0-9]+'

rc  linux-image-4.2.0-14-generic  ## The oldest kernel in the database
                                  ## Status 'rc' means it's already been removed
ii  linux-image-4.2.0-15-generic  ## The oldest installed kernel. Removable.
                                  ## Status 'ii' means Installed.
ii  linux-image-4.2.0-16-generic  ## Another old installed kernel. Removable.
ii  linux-image-4.2.0-18-generic  ## Another old installed kernel. Removalbe.
ii  linux-image-4.2.0-19-generic  ## The previous good kernel. Keep.
ii  linux-image-4.2.0-21-generic  ## Same version as 'uname -r', package for the current kernel. DO NOT REMOVE.
iU  linux-image-4.2.0-22-generic  ## DO NOT REMOVE. Status 'iU' means it's not installed,
                                  ## but queued for install in apt.
                                  ## This is the package we want apt to install.
}}}

To free space in /boot we'll remove an initrd.img file for a suitable old kernel manually, this is necessary due to a kenel packaging bug.

{{{
  $ sudo update-initramfs -d -k 4.2.0-15-generic
}}}

Now we'll use dpkg in order to TRY to purge the kernel package for the same old kernel:

{{{
  $ sudo dpkg --purge linux-image-4.2.0-15-generic
}}}

NOTE: The previous command will probably fail, as there probably is a depending linux-image-extra package installed together with a 'generic' kernel package. In general, the output of the previous command will tell which package you need to remove first. In this example case you would run

{{{
  $ sudo dpkg --purge linux-image-4.2.0-15-generic linux-image-extra-4.2.0-15-generic
}}}

Finally, we will fix the package installation process that previously failed.

{{{
  $ sudo apt-get -f install         ## Try to fix the broken dependency.
}}}

If the last command fails due to insufficient disk space in /boot, you have to purge another kernel (e.g. linux-image-4.2.0-16-generic) same way. Otherwise you could continue to chapter Manual Maintenance to remove more kernels. Make sure the linux-headers packages respective to the kernels purged above will also be purged.