SNMP is a protocol for conveying information and controlling devices over a network. SNMP can be used in two ways: Active: a device sends a command to set a parameter or request information for another device Passive: a device sends an alert (called a trap) to another device, which is configured to receive traps and […]
Monitoring with SNMP, Part 1: Fundamentals of SNMP Read More »
What do you do when you want to distribute or release source code that is stored in a Git repository? Obviously, if your target audience is using Git, you can just compress the directory that contains the repository and distribute the copies, or give the users a way to clone your repository (such as GitHub).
“Exporting” a project from a Git repository Read More »
The GENI Project is a networking testbed that is used by researchers studying novel networking technologies. While the technology is fascinating, the web site is, unfortunately, a confusing mess. Here are some pointers to get you started (or refresh your memory). This post will be updated as I learn more. Key GENI Links GENI Portal
Running network experiments on the GENI project Read More »
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
Collaborative Git workflow: Shared Repository on a File Server Read More »
Our high performance compute cluster (HPCC) has fairly primitive tools for managing the deployment of the operating system on the compute nodes. Our current tools are “aspencopy,” which takes an “image” of a the filesystem of a running server and saves it as a .tar.gz file (NOT a disk image). “aspenrestore” is its counterpart, which
Linux configuration management roundup Read More »
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
Configuring GRUB2 on Ubuntu to boot from another Linux partition Read More »
I recently installed Ubuntu on an older PC with 1GB of RAM and 80GB of hard drive space, so I wanted a lightweight desktop interface. I chose XFCE, since it is both lightweight and usable, and I have used it extensively. You can get Ubuntu pre-made with XFCE (xubuntu), but there are some disadvantages. The
Configuring XFCE4 and LightDM on a minimal Ubuntu installation Read More »
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
Preventing “soft” failures due to memory fragmentation in Linux Read More »
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
Memory fragmentation degrades performance in Linux kernels < 2.6.24 (RHEL 5.4) Read More »
It’s surprisingly difficult to find out whether it is possible to include an image from an Encapsulated PostScript (EPS) file into an Asymptote vector graphics document. It turns out that it is easy, but difficult to find in the Asymptote docs (I finally found the answer, via Google, in the FAQ). It turns out that
Insert an EPS file into an Asymptote Vector Graphics document Read More »