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3.2. Technology Previews

Technology Preview features are currently not supported under Red Hat Enterprise Linux 5 subscription services, may not be functionally complete, and are generally not suitable for production use. However, these features are included as a customer convenience and to provide the feature with wider exposure.
Customers may find these features useful in a non-production environment. Customers are also free to provide feedback and functionality suggestions for a technology preview feature before it becomes fully supported. Erratas will be provided for high-severity security issues.
During the development of a technology preview feature, additional components may become available to the public for testing. It is the intention of Red Hat to fully support technology preview features in a future release.
Stateless Linux
Included in this release of Red Hat Enterprise Linux 5 are enabling infrastructure pieces for Stateless Linux. Stateless Linux is a new way of thinking about how a system is to be run and managed, designed to simplify provisioning and management of large numbers of systems by making them easily replaceable. This is accomplished primarily by establishing prepared system images which get replicated and managed across a large number of stateless systems, running the operating system in a read-only manner (please refer to /etc/sysconfig/readonly-root for more details).
In its current state of development, the Stateless features are subsets of the intended goals. As such, the capability is being labeled as a technology preview.
The following is a list of the initial capabilities included in Red Hat Enterprise Linux 5:
  • running a stateless image over NFS
  • running a stateless image via loopback over NFS
  • running on iSCSI
It is highly recommended that those interested in testing stateless code read the HOWTO at and join
GFS2 is an evolutionary advancement based on the GFS file system. While fully functional, GFS2 is not yet considered production-ready. GFS2 is targeted to become fully supported in a subsequent Red Hat Enterprise Linux 5 update. There is also an in-place conversion utility, gfs2_convert, which can update the metadata of the older GFS file system format, converting it to a GFS2 file system.
FS-Cache is a local caching facility for remote file systems that allows users to cache NFS data on a locally mounted disk. To set up the FS-Cache facility, install the cachefilesd RPM and refer to the instructions in /usr/share/doc/cachefilesd-<version>/README.
Replace <version> with the corresponding version of the cachefilesd package installed.
Red Hat Enterprise Linux 5 features a technology preview of Xen-based virtualization capabilities for IA64, as well as the software infrastructure needed to manage a virtualized environment.
The implementation of Virtualization in Red Hat Enterprise Linux 5 is based on the hypervisor, which facilitates extremely low overhead virtualization through paravirtualization. With Intel VT-I capable processors, virtualization in Red Hat Enterprise Linux 5 also allows operating systems to run unmodified in fully virtualized mode.
Virtualization on Red Hat Enterprise Linux 5 also features the following:
  • Libvirt, a library that provides a consistent, portable API for managing virtual machines.
  • Virtual Machine Manager, a graphical utility for monitoring and managing virtual machines.
  • Virtual machine setup through the installer, as well as the ability to kickstart virtual machines.
To install the Virtualization feature, you need to use the linux debug parameter when initializing Anaconda.
Virtual machines can also be managed through Red Hat Network.
At present, the Virtualization feature has the following limitations:
  • When Virtualization is enabled, neither suspend to RAM nor suspend to disk are supported, and CPU frequency scaling cannot be performed.
  • Fully virtualized guests cannot be saved, restored or migrated.
  • The xm create command does not have a graphical equivalent in Virtual Machine Manager.
  • Virtualization only supports the bridged networking component. All corresponding tools used by guests automatically choose this as the default.
  • The default Red Hat SELinux policy for Virtualization only allows configuration files to be written to /etc/xen, log files to be written to /var/log/xen/, and disk files (including core dumps) to be written to /var/lib/xen. These defaults can be changed using the semanage tool.
  • The hypervisor included in this release of Virtualization is not NUMA-aware; as such, its performance on NUMA machines may be sub-optimal. This will be addressed in a future update of Red Hat Enterprise Linux 5.
    To work around this, enable memory node interleaving in the NUMA machine's BIOS. This ensures a more consistent performance.
  • Paravirtualized domains currently do not support keymaps other than en-US. As such, other keyboards may not be able to type certain keystrokes. This will be addressed in a future update of Red Hat Enterprise Linux 5.
  • The virtualized kernel cannot use the kdump function.
  • qcow and vmdk images are not supported. When manually configuring guests, images backed by a physical or logical device should use the phy: type. For file-backed images, set the image type to tap:aio: for paravirtualized guests and file: for fully virtualized guests.
  • Installing the kernel-xen package may lead to incorrect or incomplete elilo.conf entries. As such, you may need to manually edit elilo.conf before booting the installed kernel-xen package.
    For example, after installing the kernel-xen package, elilo.conf may read as follows:
            append="rhgb quiet"
    In this instance, the following line is missing, and will need to be added prior to boot:
  • Paravirtualized domains can only auto-detect relative mouse movement, and pointer movement is rather erratic. This will be addressed in a future update of Red Hat Enterprise Linux 5.
  • In order to have a working console for a paravirtualized guest, you need to specify console=xvc0 in the kernel command line.
  • When guest operating systems are configured to use sparse files, dom0 can run out of disk space. Such occurences prevent guest disk writes from completing, and can cause data loss in guests. Further, guests that use sparse files do not synchronize I/O safely.
    As such, it is recommended that you use non-sparse files instead. To configure guests to use non-sparse files, use the option --nonsparse when conducting a virt-install.
Compiz is an OpenGL-based compositing window manager. In addition to regular window management, compiz also acts as a compositing manager, coordinating and synchronizing the overall desktop redrawing to provide a smoother desktop experience with less flicker.
Compiz uses 3D hardware acceleration to render effects such as live thumbnail windows, window drop shadows, animated window minimizing and transitions between virtual desktops.
Due to limitations in the current rendering architecture, compiz cannot work correctly with direct rendering OpenGL applications or applications using the Xv extension. Such applications will exhibit harmless rendering artifacts; because of this, compiz is currently a technology preview.
Enhancement for Ext3
In Red Hat Enterprise Linux 5, the EXT3 file system capacity has been extended beyond 8TB to a maximum of 16TB. This capability is being included as a technology preview, and is targeted for full support in a future release of Red Hat Enterprise Linux 5.
AIGLX is a technology preview feature of the otherwise fully supported X server. It aims to enable GL-accelerated effects on a standard desktop. The project consists of the following:
  • a lightly modified X server
  • an updated Mesa package that adds new protocol support
By installing these components, you can have GL-accelerated effects on your desktop with very few changes, as well as the ability to enable and disable them at will without replacing your X server. AIGLX also enables remote GLX applications to take advantage of hardware GLX acceleration.
Frysk GUI
The goal of the frysk project is to create an intelligent, distributed, always-on system monitoring and debugging tool that allows developers and system administrators to:
  • monitor running processes and threads (including creation and destruction events)
  • monitor the use of locking primitives
  • expose deadlocks
  • gather data
  • debug any given process by choosing it from a list or allowing frysk to open a source code (or other) window on a process that is crashing or misbehaving
In Red Hat Enterprise Linux 5 the frysk graphical user interface is a technology preview, whereas the frysk command line interface is fully supported.
Systemtap provides free software (GPL) infrastructure to simplify the gathering of information about the running Linux system. This assists diagnosis of a performance or functional problem. With the help of systemtap, developers no longer need to go through the tedious and disruptive instrument, recompile, install, and reboot sequence that may be otherwise required to collect data.
Dogtail is a GUI test tool and automation framework written in Python that uses Accessibility technologies to communicate with desktop applications.
Support for Indic Languages and Sinhalese
Red Hat Enterprise Linux 5 also features support for the following languages as technology preview:
  • Assamese
  • Kannada
  • Sinhalese
  • Telugu
For more information about how to install and enable support for these languages, refer to the Internationalization section of this document.
Installing to dm-multipath Devices
Anaconda now has the capability to detect, create, and install to dm-multipath devices. To enable this feature, add the parameter mpath to the kernel boot line.
Note that the parameter mpath may cause a boot failure if a device's major:minor number changes. This issue will be addressed in a future update of Red Hat Enterprise Linux 5.
Installation / Boot for iSCSI software initiator (open-iscsi)
Anaconda now provides the ability to install to an iSCSI device. Booting and installing is fully supported with the QLogic qla4xxx hardware initiator. However, the capability to install to an iSCSI device for the open-iscsi software initiator is currently considered a Technology Preview, due to the following issues:
  • Text mode installation does not complete. You must do a graphical install, or an automated kickstart install.
  • Media-based installations do not complete. You must do a network-based install.
  • Depending on the timing of events, Anaconda may be unable to detect all the iSCSI targets or LUNs. When this occurs, use the installer shell to configure the storage through iSCSI commands.
  • The iscsid daemon may not properly start. Such an occurence will prevent the system from handling all iSCSI errors, such as network problems, SCSI/iSCSI timeouts, and target errors. To confirm that the iscsid daemon is running, run the command iscsiadm -m session -i and check that the line, Internal iscsid Session State: reports a value (it can be any value).
  • On certain iSCSI target implementations, the system may hang during shutdown.
  • On certain iSCSI target implementations, the system may hang during reboot. To avoid this, shutdown the system and boot it up again (instead of rebooting directly from a session).
  • Booting from iSCSI devices on the IBM System p does not work reliably. While installation on an iSCSI device may appear to succeed, the resulting installation will not boot properly.
  • On the first boot after install, you may receive SELinux errors such as the following:
    kernel: audit(1169664832.270:4): avc:  denied  { read
    } for  pid=1964 comm="iscsid"
    To work around this, boot the system with the kernel parameter enforcing=0. Once the system has properly booted, use the command setenforce 1 to restore enforcing mode.
These limitations will be addressed in a future Red Hat Enterprise Linux 5 update.