Three Methods of Executing Commands on Many Nodes in Parallel via SSH on Linux

It is common to execute commands on many nodes/hosts via SSH for managing a cluster of Linux servers. On Linux, there are many choices for this task. Generally, to run commands on many nodes, there are two modes: serial mode and parallel mode. In serial mode, the command is executed on the node one by […]

Tutorial Video for “PHP Function for Fetching RSS Feed and Outputting Feed Items as HTML”

After the post A PHP Function for Fetching RSS Feed and Outputing Feed Items as HTML was originally published, there are some updates such as adding a simple RSS feed caching mechanism and supporting scanning content parts of the feed items for images. Recently, Webucator makes a great tutorial video on introducing the RSS to […]

Running a Command Upon Files or Directories Changes on Linux

Doing actions upon changes of files and directories is very useful. Examples like compiling a project after the source code files are changed, sending emails after important configuration files are modified, building the PDF after a TeX file is modified. On Linux, the inotify-tools provide good support for trigger actions after changes. In this post, […]

A posix_spawn Example in C to Create Child Process on Linux

The posix_spawn() and posix_spawnp() functions create a new child process from the specified process image constructed from a regular executable file. It can be used to replace the relative complex “fork-exec-wait” methods with fork() and exec(). However, compared to fork() and exec(), posix_spawn() is less introduced if you search on the Web. The posix_spawn() manual […]

Keyboard Key Mapping for Emacs: Evil Mode and Rearranging Alt, Ctrl and Win Keys

Ctrl keys are important and possibly most frequently used in Emacs. However, it is painful on today’s common PC keyboards since Ctrl keys are usually in the corner of the keyboard main area. Why the key mappings in Emacs are designed like this? After it was designed, Emacs was commonly on the Lisp Machine keyboards […]

Git Merging FAQs

git merge is frequently used during development of projects managed by git. There are many common questions about git merge and I find most are solved and discussed on StackOverflow. Here, I summarize useful ones so that others who want to learn git merge need to do the search again. Merge, rebase, fast forward and […]

Speeding Up WordPress with APC Object Cache and WP Super Cache

WordPress can be very fast after some (small) effort on performance optimization with the help from its plenty of plugins. Two of the directions are using cache to cut down the number of database queries and optimizing PHP’s performance with opcode cache. In this post, we introduce how to speed up WordPress with APC object […]