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RedHat Enterprise Linux 4 AS Distribution 

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PCQ Bureau
New Update

RedHat has upped the ante with this release of its enterprise Linux. Compared to RHEL 3, this one has support for 16 more 32-bit CPUs or 56 more 64-bit CPUs. It can also run on more architectures-x86, Itanium, EM64T, AMD64 and the IBM Power Series. RHEL 4 supports PCI-Express (Gigabit Ethernet). RedHat has chosen the 2.6.9 kernel which is very stable. 

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SELinux is being billed as the best security system around, but its configurability is still a major issue-the 'system-config-securitylevel' interface features far too few options or rules for an enterprise's needs. Much of it still needs to be done over complicated CLI commands and this is not easy. The Linux file system sees an improvement with the addition of features to Ext3 that sees it addressing storage up to 8 TB. Better I/O algorithms in the 2.6.9 kernel, like noop, deadline, anticipatory and complete fair queue (CFQ) scheduling make for better application performance. To enable these schedulers, you need to pass parameters on the boot command-line. The noop scheduler performs no optimization at all and is suitable for memory sticks, USB drives and virtual storage. Deadline reduces wait-periods for processes by monitoring how much time each of them waits for data. Anticipatory scheduling will pre-fetch data from areas surrounding the current data and this works best for sequential information and database retrievals. CFQ reduces I/O bandwidth usage across applications by dividing the available I/O time between all running processes. 

The current release has no method to select this on a per-device basis, however, a patch is available to let a script write a value to a block-device's configuration file and change its scheduler dynamically. You can read more about it at

http://lwn.net/Articles/50685.

Samba can now be configured with WinBind authentication that allows it to connect to Windows Active Directory Servers 

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Like SUSE Linux (we reviewed it in March 2005), RHEL 4 bundles Samba 3.0 and hence includes the WinBind authentication module that lets it integrate with Active Directory servers on your network in one easy step. 'system-config-samba' is the tool you would look for configuring this. LVM (Logical Volume Management) is now version 2 and includes tools in GNOME that helps you perform tasks like volume expansion, shrinkage, mirroring and striping easily. CLI tools (lv* commands) help you do the same too.

RHEL 4 is supposed to see a new service called 'audit' which is to replace the aging LAus daemon for system auditing. This service is slated for debut later this year. 

This should improve single-point management functions in a typical enterprise scenario. Another worthy addition to RHEL 4 is the ExecShield and PIE (Position Independent Execution) prevention system that blocks execution of programs from unauthorized locations-much like the Windows' DEP (Data Execution Prevention) system.

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Compared to other enterprise OSs such as SUSE Linux or the Windows Server 2003, RHEL 4 still has a long way to go in the realm of administrative flexibility and ease. But given its stability, you would only need to configure it and perform minimal maintenance through

Webmin. 

Bottom Line: Much improved release of RHEL, well suited to its role of serving mission-critical environments. 

Sujay V Sarma

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