SysAdmin

The namei command walks a full path and prints ownership, permissions, and symbolic link resolution for every component. It is a quick way to spot where a permission chain breaks or a symlink redirects unexpectedly.

How to set the HDFS Namenode StateChange log level to DEBUG via the web UI or the command line, and when that helps with troubleshooting.

A host health test flags NTP clock drift when the system clock falls out of sync with its NTP servers. This guide walks through diagnosing and resolving common NTP synchronization failures.

Mod_rewrite is a rule-based rewriting engine (based on a regular-expression parser) to rewrite requested URLs on the fly.

Have you ever replaced a network interface (NIC) or performed a chassis swap? If you are an administrator or IT professional the chances are good that at some point or another you have had to deal with sticky udev rules.

Postfix is a free and open-source mail transfer agent (MTA) that routes and delivers electronic mail. This post covers core system concepts.