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The "OutOfMemoryError: PermGen space" message is normally encountered during development activites where a long-running JVM is asked to load/unload builds. However it can also be encountered in a recently spawned JVM under the "right" set of conditions. The message is a symptom of an incomplete garbage collection sweep where resources are not properly released upon unload/restart...

Intrusions can take place from both authorized (insiders) and unauthorized (outsiders) users. My personal experience shows that unhappy user can damage the system, especially when they have a shell access. Some users are little smart and removes history file (such as ~/.bash_history) but you can monitor all user executed commands...

Many people hack together shell scripts quickly to do simple tasks, but these soon take on a life of their own. Unfortunately shell scripts are full of subtle effects which result in scripts failing in unusual ways. It's possible to write scripts which minimise these problems. In this article, I explain several techniques for writing robust bash scripts...

Have you ever wanted to change the names of many files at once? Or, have you ever needed to use a default value for a variable that has no value? These and many other options are available to you when you use string operators in bash and other Bourne-derived shells...

mod_cache has been around for a while, but there are some new features in it that can help you make better use of your server's resources. Although people have traditionally used the caching capabilities of mod_cache with proxied content, that isn't its only feature. You can also cache your dynamic content and serve it as rapidly as on-disk files...

PostgreSQL has a powerful user authentication and access control system, but for a newcomer, it can seem confusing and overwhelming. In this article I hope to explain how to manage user and permissions with ease...

If you have expensive computer systems running in your data center, you want to make sure they keep running smoothly. Server vendors have addressed this by adding system monitoring devices to motherboards to report on temperatures, fan speeds, and voltages.

The standard way to monitor these parameters has traditionally been with tools such as lm_sensors on systems running Linux. However, this mechanism is far from perfect. For starters, it can be incredibly difficult to configure lm_sensors correctly because of poor documentation...

To test your website before DNS propagation has completed you can edit the HOSTS file on your local computer. Your computer will use the entries in your HOSTS file before it looks up the current information in DNS. This walkthrough will explain how to edit the HOSTS file on Windows 98/Me/2000/XP/2003/Vista computers as well as on Apple Mac OS 9 and OS X machines.

Typical Unix users cringe at the thought of putting spaces in file names. Mac users, on the other hand, frequently put spaces in file names because it's natural and may read better. This means that Mac OS X Unix geeks need to make sure their shell commands (and shell scripts) work correctly when faced with spaces in file names. Below is outlined a few simple ways to properly deal with this...

SQL*Plus is a command line SQL and PL/SQL language interface and reporting tool that ships with the Oracle Database Client and Server software. It can be used interactively or driven from scripts. SQL*Plus is frequently used by DBAs and Developers to interact with the Oracle database.