Xen 4.2 Release Notes

= Overview =
* Xen 4.2.0 was released on 17 September 2012. Announcement on xen.org blog: http://blog.xen.org/index.php/2012/09/17/xen-4-2-0-released/ and on xen-devel mailinglist: http://lists.xen.org/archives/html/xen-devel/2012-09/msg01271.html .
* Xen 4.2.1 was released on 18 December 2012. Announcement on xen.org blog: http://blog.xen.org/index.php/2012/12/18/xen-4-2-1-and-4-1-4-released/ and on xen-devel mailinglist: http://lists.xen.org/archives/html/xen-devel/2012-12/msg01288.html .
* Xen 4.2.2 was released on 25 April 2013. Announcement on xen.org blog: http://blog.xen.org/index.php/2013/04/25/xen-4-1-5-4-2-2-xen-document-and-xen-4-3-test-days/ and on xen-devel mailinglist: http://lists.xen.org/archives/html/xen-devel/2013-04/msg02560.html .
= New Features =
Xen 4.2 contains many new features and improvements to existing functionality. Changes include improvements to Security, Scalability, Performance, RAS, Documentation and to the toolstack.
For a list of new features and changes see Xen 4.2 Feature List and comparison of features in Xen 4.x versions.
== Default Toolstack ==
XL is now the default toolstack supplied with Xen. Please see the XL page for guidance on migrating from XEND.
See the XL_vs_Xend_Feature_Comparison wiki page for more information about features supported in XL vs. XM/XEND.
The XEND toolstack is now deprecated and should be expected to be removed in the 4.3 timescale. Therefore it is strongly recommended that users evaluate Xen 4.2 with XL for their use cases and report any omissions or blockers such that they can be addressed for 4.3. Fixes for serious functionality gaps will also be considered for backport to the 4.2.x releases.
= Build Requirements =
The requirements for building Xen are documented in the README file in the Xen source tree.
Some additional build dependencies have been added since Xen 4.1 and Xen 4.0:
* libyajl
* glib
* pkg-config
* markdown (optional)
In addition Xen will now prefer to use the system wide libaio if it is available. If libaio is not installed then an in tree version will be used. Users are strongly encouraged to install their distribution's version of libaio.
An additional step has also been added to the build process. It is now necessary to run:
 $ ./configure
before building the tools (e.g. make tools, make world, make dist etc).
As a consequence of this change Xen now defaults to installing libraries into /usr/lib by default. Users on systems which use /usr/lib64 for 64-bit libraries should use the --libdir option. e.g:
 $ ./configure --libdir=/usr/lib64
= Build instructions / tutorials = 
* Information about build dependencies, required packages for common Linux distributions and building Xen from sources please see the Compiling_Xen_From_Source wiki page. 
* Also a separate wiki page is available for RHEL, CentOS or Fedora users for information specific to these distributions Xen_4.2_Build_From_Source_On_RHEL_CentOS_Fedora.
* Also see the Xen 4.1 and especially Xen 4.0 release notes wiki pages for a list of build dependencies and required packages for rpm/deb based distros.
= Known issues =
* XL's default configuration is not compatible with driver domains. To use driver domains with XL you should set run_hotplug_scripts=0 in /etc/xen/xl.conf.
* On systems running a 32-bit hypervisor xl info will report incorrectly report large values for sharing_used_memory and sharing_freed_memory. Memory sharing is not supported on the 32-bit hypervisor and these should read zero.
* When using XL toolstack and "dom0_mem=" option for Xen hypervisor in grub you need to disable xl autoballoon in xl.conf, otherwise launching VMs will fail with errors about not being able to balloon down dom0. So add "autoballoon=0" to xl.conf if you have dom0_mem= option specified for Xen. Also see http://wiki.xen.org/wiki/Xen_Best_Practices#Xen_dom0_dedicated_memory_and_preventing_dom0_memory_ballooning .
Category:Xen Category:Xen 4.2 Category:Release Notes Category:Users Category:Beginners