New in Red Hat Enterprise Linux, Version 4.0

Introduced in February 2005, Red Hat Enterprise Linux v.4 provides significant technology enhancements, including the following new features:

Linux 2.6 kernel infrastructure

Red Hat Enterprise Linux v.4 provides the most stable and robust commercial product based on the Linux community's 2.6.9 kernel. Open source projects such as Fedora provided an environment for the Linux 2.6 kernel to mature significantly during 2004. As a result, the Red Hat Enterprise Linux v.4 kernel offers numerous improvements over earlier kernels, including many enhanced algorithms and features:

Generic logical CPU scheduler:
Handles multi-core and hyperthreaded CPUs.
Object-based Reverse Mapping VM:
Improved performance in memory constrained systems.
Read Copy Update:
SMP algorithm optimization for operating system data structures.
Multiple I/O schedulers:
Selectable based on the application environment.
Enhanced SMP & NUMA support:
Improved performance and scalability for large servers.
Network interrupt mitigation (NAPI):
Improved performance for heavy network loads.

Improved storage and file system capabilities

Numerous enhancements have been incorporated into Red Hat Enterprise Linux v.4 that improve the scalability and performance of the data storage subsystems, including:

Ext3 performance:
Block Reservations and Hash Tree Directories improve the performance of read/write I/O and directory scanning operations.
Ext3 scalability:
Dynamic file system expansion and file system sizes up to 8TB are now supported.
Logical Volume Management:
A comprehensive update to the LVM provides new features such as read/write snapshots and transactional metadata updates, along with a flexible new management GUI.
Scalability:
Enhanced storage LUN management makes it possible to configure much larger storage subsystems.
Automounting:
The inclusion of AutoFSv4 provides sophisticated device access control, supporting features such as browsable mounts and replicated servers.
Cost reduction:
Support for Serial ATA disk storage provides increased performance, higher densities, and reduced cost per megabyte over traditional IDE devices.

New security capabilities

Provision of sophisticated security capabilities has been a specific development focus of the Red Hat Enterprise Linux v.4 release. New features include:

Mandatory Access Control:
Security Enhanced Linux (SELinux) provides a MAC infrastructure that complements the existing Discretionary Access Control security features provided by the standard Linux environment. In a MAC-based environment, application capabilities and privileges are set by predefined policies and enforced by the kernel. This prevents errant applications from compromising system security.
Memory management enhancements:
Several features, including Exec Shield and Position Independent Executables, combine to prevent applications from being exploited by attacks such as buffer overflows.
Compile and runtime consistency checking: New buffer validation techniques in the GCC compiler and Glibc library greatly reduce the risk of faulty applications being compromised.

Miscellaneous features

As a major new release, almost every aspect of Red Hat Enterprise Linux has been enhanced. Some of the more important improvements:

Compatibility with prior releases:
Red Hat Enterprise Linux v.4 includes compatibility libraries that enable most v.3 and v.2.1 applications to continue to run without modification.
Languages:
Focused on international standards, such as OpenI18N and GB18030, Red Hat Enterprise Linux has documentation and software available in 15 languages: English, Japanese, German, Brazilian Portuguese, Korean, Italian, French, Simplified Chinese, Traditional Chinese, Spanish, Devnagari, Bangla, Punjabi, Tamil, Gujarati.
File serving:
Provision of NFSv4 provides features such improved security, operation coalescing and integrated file locking, while Samba provides easy access to Microsoft Windows printers and file shares.
Software development:
The latest GCC 3.4 compiler toolchain, and a technology preview of the forthcoming GCC 4.0 toolchain, are provided. These offer standards-compliant C/C++ and Fortran 95 development environments.
Advanced configuration and power interface:
Support for the ACPI standard enables a wide range of power management capabilities (battery monitoring, automated power down, suspend), and provides a foundation for increasingly sophisticated features in the future.