######
Kernel
######

Disable bios network names
==========================

* Edit /etc/default/grub and add the following to GRUB_CMDLINE_LINUX

.. code-block:: bash

  net.ifnames=0 biosdevname=0

* Run the command update-grub
  
  
USB shuts itself down
=====================

* Append ``usbcore.autosuspend=-1``  to kernel parameters


What is load?
=============

* With a quad core system a load average of 5 means that all 4 cpus are busy for 100% and processes to fill another cpu are waiting
* http://blog.scoutapp.com/articles/2009/07/31/understanding-load-averages

.. code-block:: bash

  cat /proc/loadavg

* field 1-3 = load average of jobs in the run queue (state R) or waiting for disk I/O (state D) averaged over 1, 5, and 15 minutes
* field 4 = number of currently runnable kernel scheduling entities (processes, threads) / number of kernel scheduling entities that currently exist on the system
* field 5 PID of the process that was most recently created on the system

Hide other users processes
==========================

* Add hidepid=2 to fstab mount options

.. code-block:: bash

  proc                    /proc                   proc    nosuid,noexec,nodev,hidepid=2 0 0
  

Find out which driver is in use
===============================

* network card

.. code-block:: bash

  ls -al /sys/class/net/eth5/device/driver/module

* generic

.. code-block:: bash

  lspci | grep VGA
  02:00.0 VGA compatible controller: Matrox Electronics Systems Ltd. MGA G200e [Pilot] ServerEngines (SEP1) (rev 02)

  find /sys | grep driver.*02:00

* or more easy

.. code-block:: bash

  lspci -vv


Use old network device names
============================

* Start kernel with the parameters ``net.ifnames=0 biosdevname=0``
* Or disable automatic renaming in udev

.. code-block:: bash

  ln -s /dev/null /etc/udev/rules.d/80-net-setup-link.rules

* Or rename devices with udev

.. code-block:: bash

  cat > /etc/udev/rules.d/99-rename-to-eth0.rules << EOF
  SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="$(cat /sys/class/net/ens33/address)", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"
  EOF


Availale parameters for kernel module
======================================

.. code-block:: bash

  modinfo <module_name>


Show current kernel boot parameters
===================================

.. code-block:: bash

  cat /proc/cmdline


Hotplug CPUs
============

* Enable

.. code-block:: bash

  echo 1 > /sys/devices/system/cpu/cpu<No>/online

* Disable

.. code-block:: bash

  echo 1 > /sys/devices/system/cpu/cpu<No>/online


Reload CPU microcode without reboot
===================================

.. code-block:: bash

  echo 1 > /sys/devices/system/cpu/microcode/reload


Check if virtualization is enabled
==================================

.. code-block:: bash

  grep vmx /proc/cpuinfo


Check if TPM is available
=========================

.. code-block:: bash

  grep smx /proc/cpuinfo


Hide kernel symbols
===================

* Create /etc/sysctl.d/50-kptr-restrict.conf

.. code-block:: bash

  kernel.kptr_restrict = 1