Linux

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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Collaborative Git workflow: Shared Repository on a File Server

GitHub is a great tool for collaborating on projects. However, sometimes it is necessary to mimic the “GitHub workflow” using a shared repository on a local Linux server. The following example shows how I shared an example repository with multiple users.  We are also using the Git flow model for branching, aided by the handy …

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Configuring GRUB2 on Ubuntu to boot from another Linux partition

My recent Ubuntu installation was my first experience with the new GRUB 2.x series of bootloaders. Unforunately, the process of manually configuring GRUB2 on Ubuntu is not well documented in the case that everything doesn’t work “automagically.” I had to solve two problems: the blank screen at boot, and getting GRUB to boot to an …

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Preventing “soft” failures due to memory fragmentation in Linux

A previous post documented that a Linux server running a pre-2.6.24 kernel can fail to allocate large chunks of memory after its memory has been fragmented by a “thrashing” incident. In this post, I will point out some ways to prevent this problem. Use a Newer Kernel We have some servers running RHEL 5.9 with …

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Memory fragmentation degrades performance in Linux kernels < 2.6.24 (RHEL 5.4)

I have data from the STOKES High Performance Compute Cluster which definitively shows that kernel versions prior to 2.6.24 can suffer significant performance degradation due to memory fragmentation. I noticed the problem on servers running Red Hat Enterprise Linux (RHEL) 5.4 with kernel version 2.6.18-164.el5. This post will document my findings. The graphs were taken …

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