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Courier IMAP SSL Server Certificate Installtion and Configuration

The Courier mail server is a mail transfer agent (MTA) server that provides ESMTP, IMAP, POP3, webmail, and mailing list services with individual components. But, it is best known for its IMAP / IMAPs and POP3 / POP3s (secure version) server component.

Courier can provides support for both regular UNIX operating system account (stored in /etc/passwd) and virtual mail account managed by third party backends such as OpenLDAP, MySQL and so on.

In this quick tutorial, you will learn about installing Courier IMAP SSL digital certificate.
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VMWare ESX4 and ESX3.5: SCSI timeout For Linux Guest

Recently, I noticed that the timeout values differ on CentOS v5.x and RHEL Linux 5.x guests on VMWare ESX4 and ESX3.5. I've notices that older ESX 3.5 set a 60 secs timeout and ESX4.x set to 180 secs. Luckly you can fix it easily:
Edit /etc/udev/rules.d/99-vmware-scsi-udev.rules,
# vi /etc/udev/rules.d/99-vmware-scsi-udev.rules
Sample config:

RUN+="/bin/sh -c 'echo 180 >/sys$DEVPATH/device/timeout'"

Find timeout value (180) and change it as per your requirements. Make sure you install the vmware-tools RPM.

XEN Virtualization Set The MTU For xenbr0 Interface

I've already written about setting the MTU (Maximum Transmission Unit) under Linux including Jumbo frames (FreeBSD specific MTU information is here).

With this quick tip you can increase MTU size to get a better networking performance.
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Top 10 Linux Virtualization Software

Virtualization is the latest buzz word. You may wonder computers are getting cheaper every day, why should I care and why should I use virtualization? Virtualization is a broad term that refers to the abstraction of computer resources such as:

  1. Platform Virtualization
  2. Resource Virtualization
  3. Storage Virtualization
  4. Network Virtualization
  5. Desktop Virtualization

This article describes why you need virtualization and list commonly used FOSS and proprietary Linux virtualization software.
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Apache2 mod_fastcgi: Connect to External PHP via UNIX Socket or TCP/IP Port

Now, mod_fastcgi is configured and running. FastCGI supports connection via UNIX sockets or TCP/IP networking. This is useful to spread load among various backends. For example, php will be severed from and python / ruby on rails will be severed from This is only possible with mod_fastcgi.
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Red Hat / CentOS Apache 2 FastCGI PHP Configuration

FastCGI is a protocol for interfacing interactive programs with a web server. FastCGI's main aim is to reduce the overhead associated with interfacing the web server and CGI programs, allowing a server to handle more web page requests at once.

Also, PHP is not recommended with multithreaded Apache2 (worker MPM) because of performance and some 3rd party PHP extensions are not not guaranteed thread-safe.

nginx and lighttpd has inbuilt support for FastCGI. For Apache web server you need to use either mod_fastcgi or mod_fcgid.

Why use mod_fastcgi instead of mod_perl / mod_php?

From the wikipedia article:

Instead of creating a new process for every request, FastCGI can use a single persistent process which handles many requests over its lifetime. Processing of multiple requests simultaneously is achieved either by using a single connection with internal multiplexing (ie. multiple requests over a single connection) and/or by using multiple connections. Many such processes can exist, something that can increase stability and scalability. FastCGI also allows programs to get the web server to do certain simple operations, like reading in a file, before the request is handed over. Environment information and page requests are sent from the web server to the process over a TCP connection (for remote processes) or Unix domain sockets (for local processes). Responses are returned from the process to the web server over the same connection. The connection may be closed at the end of a response, but the web server and the process are left standing.

Many web site administrators and programmers are finding that the separation of web applications from the web server in FastCGI (and the simpler SCGI) has many desirable advantages over embedded interpreters (mod_perl, mod_php, etc.). This separation allows server and application processes to be restarted independently -- an important consideration for busy web sites. It also facilitates per-application security policies -- important for ISPs and web hosting companies.

In this quick tutorial, you will learn about Apache 2 + mod_fastcgi + PHP installation and configuration under Red Hat Enterprise Linux / CentOS Linux version 5.x+.
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Free Software Foundation Filed GPL Violations Suit Against Cisco

The Free Software Foundation (FSF) - a non-profit corporation founded by Richard Stallman; today announced that it has filed a copyright infringement lawsuit against Cisco. The FSF's complaint alleges that in the course of distributing various products under the Linksys brand Cisco has violated the licenses of many programs on which the FSF holds copyright, including GCC, binutils, and the GNU C Library. In doing so, Cisco has denied its users their right to share and modify the software.
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