Linux

Warning: CentOS/RedHat 7.4 installs FreeRADIUS 3 with breaking changes

When you run yum upgrade on a CentOS/RedHat 7 instance, you will be upgraded to 7.4. If you have a FreeRADIUS server, you will be upgraded from version 2 to 3, and your server will likely stop authenticating! Good times! Fortunately, the solution was not complicated for us, because we had good documentation. Symptoms Your …

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Managing persistent disks on Google Compute Engine

It can confusing when you have multiple persistent disks on an instance running on Google Compute Engine. For example, a server may have separate disks for the filesystem root, MySQL data, logs, and /tmp. Once you’ve created the Compute Engine disks and attached each one to the instance, how do you know which Compute Engine …

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Monitoring with SNMP, Part 3: Automate active monitoring with Nagios

My last post showed how to monitor networked devices with SNMP. You could try to remember to manually check the status of things periodically, but that would be missing the point of computers. Instead, automate your monitoring with Nagios, a web-based monitoring tool for Linux that automates the process of actively querying devices and doing …

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Monitoring with SNMP, Part 2: Command-line tools for active SNMP

In Part 1, I summarized the basic concepts of SNMP and defined the terms and acronyms used in this post. Now, I will show how to use SNMP to monitor actual devices. As an example, I will monitor an enterprise-grade uninterruptible power supply (UPS) and power distribution unit (PDUs) from Tripp-Lite. These devices have an …

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