Today Red Hat released the fourth update of Red Hat Enterprise Linux 6. After 8 months there's also another update that brings a lot of fixes and new features.

The Release Notes für RHEL 6.4 are, as usual, very considerably - I personally think, that the following updates are specially mentionable:

Kickstart

Using th fcoe, vlanid, bondslaves and bondopts options, it is now possible to use Fibre-Channel-over-Ethernet devices, VLANs and network bonds for kickstart installations.

Technology Previews

In RHEL 6.4, two applications found their way as "technology previews" into the operating systems. These applications aren't released for productive usage yet - they should be used for testing purposes.

One of these applications is Samba 4, which had been released a few months ago. The new version of Samba ist the first Linux/Unix directory service which is fully compatible to Microsoft Active Directory Services. The development time of Samba 4  was 6 years - the application is more or less a complete re-programming of Samba.

With HAProxy, a network load-balancer for TCP and HTTP applications was introduced.

Security

The PAM module pam_cracklib was updated and supports now also reading the optional GECOS field of the user database. Additional information like first/last/company name of a user is noticed. While creating passwords, pam_cracklib is able to make sure that parts of this field are excluded to enhance the password security. Using the option enforce_for_root this security enhancement can also be forced for the local administrator account.

IPTables now supports fallback configurations. If the main firewall configuration (/etc/sysconfig/iptables) can't be loaded for some reason, it is possible to load a additional fallback configuration (/etc/sysconfig/iptables.fallback).

Virtualization

Red Hat Enterprise Linux 6 now comes with full Hyper-V support (including Balooning). Virtual installations on Hyper-V environments are integrating better and work with better performance.

The paravirtual driver family for VMware vSphere Hypervisor (ESXi) had been updated. As an addition it is now possible to use shared VMDK hard drive for cluster purposes. Using this, it is possible to use OCF2 volumes on appropriate configured VMDK volumes.

CPU configuration using chcpu

There is also a new tool named chcpu which can be used for configuring, enabling and disabling procsesors.

Using this, it is possible to define the way how processes are allocated (polarized) - they can be allocated "horizontally" on all available CPUs or "vertically" on some defined ones.

CPUs can be enabled or disabled as easy as pie:

1# grep processor /proc/cpuinfo
2processor       : 0
3processor       : 1
4# chcpu -d 1
5# grep processor /proc/cpuinfo
6processor       : 0

Additional changes

The Linux kernel had been updated from version 2.6.32-279 to 2.6.32-358.

Samba now supports Kerberos AES for more security on Windows 2008/2008R2/7/8 clients.