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Linux: 20 Iptables Examples For New SysAdmins

Linux comes with a host based firewall called Netfilter. According to the official project site:

netfilter is a set of hooks inside the Linux kernel that allows kernel modules to register callback functions with the network stack. A registered callback function is then called back for every packet that traverses the respective hook within the network stack.

This Linux based firewall is controlled by the program called iptables to handles filtering for IPv4, and ip6tables handles filtering for IPv6. I strongly recommend that you first read our quick tutorial that explains how to configure a host-based firewall called Netfilter (iptables) under CentOS / RHEL / Fedora / Redhat Enterprise Linux. This post list most common iptables solutions required by a new Linux user to secure his or her Linux operating system from intruders.
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Download CentOS 6 CD / DVD ISO

CentOS Linux version 6 has been released. It is a community-supported operating system based on Red Hat Enterprise Linux (RHEL) version 6. CentOS Linux is considered as the most popular Linux distribution for web servers with almost 30% of all Linux servers using it.
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Server provisioning is nothing but load the Linux or UNIX like operating systems automatically with actual operating systems, device drivers, data, and make a server ready for network operation without any user input. Typically you select a server from a pool of available servers, load the operating systems (such as RHEL, Fedora, FreeBSD, Debian), and finally customize storage, network (IP, gateway, bounding etc), drivers, applications, users etc. Using the following tools you can perform automated unattended operating system installation, configuration, set virtual machines and much more. These software can be used to install a lot (say thousands) of Linux and UNIX systems at the same time.
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CentOS Linux Project In Trouble

CentOS is a community-supported, freely-available operating system based on Red Hat Enterprise Linux. Lance Davis created CentOS and now he goes absent without leave. In an open letter from his fellow CentOS developers:

You have long promised a statement of CentOS project funds; to this date this has not appeared. You hold sole control of the centos.org domain with no deputy; this is not proper. You have, it seems, sole 'Founders' rights in the IRC channels with no deputy ; this is not proper.

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Install Linux On Intel Xeon 7400 Dunnington

Dunnington is Intel's first multi-core CPU - features a single-die six- (or hexa) core design with three unified 3 MB L2 caches (resembling three merged 45 nm dual-core Wolfdale dies), and 96 KB L1 cache (Data) and 16 MB of L3 cache. It features 1066 MHz FSB, fits into the Tigerton's mPGA604 socket, and is compatible with the Caneland chipset. These processors support DDR2-1066 (533 MHz), and have a maximum TDP below 130 W. They are intended for blades and other stacked computer systems.

I've Sun Blade X6450 server for ERP application:

The four-socket Sun Blade X6450 server module features Intel Xeon processor 7000 series and up to 192 GB of memory. With 24 DIMM slots per server module, it gives you 50 percent more memory capacity than competing blade servers making it an ideal fit for virtualization and server consolidation, HPC, database and enterprise applications. Fill a Sun Blade 6048 chassis for a remarkable 11TFLOPS of peak performance and up to 1152 processing cores per rack.

Fig.01: Sun Blade X6450 Server Module showing the internals

Fig.01: Sun Blade X6450 Server Module showing the internals

I tried old RHEL version and it failed to work because of old kernel. So I called to Redhat support and they told me to use at least kernel 2.6.18-92.1.10 and above. The problem is my client do not have RHEL 5.2 media and License (server came with Solaris 10). So I asked my client to get RHEL 5.2. Unfortunately, their local software vendor was out of stock for RHEL software. It took 5 days to get software media kit.

Finally, I've installed it on Sun blade server. It is working fine now. I wish I knew about latest Intel Xeon 7400 support problem earlier. It may have saved some time, effort, traveling and money on my part. I should have gone though server datasheet. This server only works with RHEL version 4.7 or 5.2 (32/64 bit) and above.

Red Hat today released kernel updates to fix at least 15 security flaws in its core called Linux kernel. RHEL users can grab the latest updates from RHN website or by simply running yum update command. This update has been rated as having important security impact.
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Install Linux on Fujitsu Siemens ESPRIMO E5720

I was trying to install Redhat ( RHEL 5) / CentOS 5 server on a Fujitsu Siemens ESPRIMO E5720 and got problem with the installer.

The base resolution for CentOS / RHEL Linux 5 is 800x600x32, which requires 2MB video memory. In order to boot or install Linux on the Fujitsu Siemens ESPRIMO E5720, set the reserved amount of video RAM to 8MB in BIOS.

You also need to add pci=nommconf parameter to grub.conf boot option file. While installing Linux on Fujitsu Siemens ESPRIMO E5720, you need to type the following at a boot prompt (excluding boot: word itself):
boot: linux pci=nommconf
Once server is installed, edit /etc/grub.conf or /boot/grub/grub.conf and append pci=nommconf at the end of kernel line:

title Red Hat Enterprise Linux Server (2.6.18-128.el5)
	root (hd0,0)
	kernel /vmlinuz-2.6.18-128.el5 ro root=LABEL=/ console=tty0 console=ttyS1,19200n8 pci=nommconf
	initrd /initrd-2.6.18-128.el5.img