Varda: The Mysterious Fiber Bomb Problem: A Debugging Story

By jake Over at the Sandstorm Blog, project founder Kenton Varda relates a debugging war story. Sandstorm web servers would mysteriously peg the CPU around once a week, slowing request processing to a crawl, seemingly at random.
Obviously, we needed to take a CPU profile while the bug was in progress. Of course, the bug only reproduced in production, therefore we’d have to take our profile in production. This ruled out any profiling technology that would harm performance at other times – so, no instrumented binaries. We’d need a sampling profiler that could run on an existing process on-demand. And it would have to understand both C++ and V8 Javascript. (This last requirement ruled out my personal favorite profiler, pprof from google-perftools.)

Luckily, it turns out there is a correct modern answer: Linux’s “perf” tool. This is a sampling profiler that relies on Linux kernel APIs, thus not requiring loading any code into the target binary at all, at least for C/C++. And for Javascript, it turns out V8 has built-in support for generating a “perf map”, which tells the tool how to map JITed code locations back to Javascript source: just pass the –perf_basic_prof_only_functions flag on the Node command-line. This flag is safe in production – it writes some data to disk over time, but we rebuild all our VMs weekly, so the files never get large enough to be a problem.”

From: LWN


Why Good Linux Sysadmins Use Markdown

By Carla Schroder The life of a Linux system administrator is complex and varied, and you know that documenting your work is a big time-saver. A documentation web server shared by you and your colleagues is a wonderful productivity tool. Most of us know simple HTML, and can whack up a web page as easily as writing plain text. But using Markdown is better.

From: LXer


ownCloud Desktop Client 2.2.4 Released with Updated Dolphin Plugin, Bug Fixes

By Softpedia News (Marius Nestor)

ownCloud is still alive and kicking, and they’ve recently released a new maintenance update of the ownCloud Desktop Client, version 2.2.4, bringing some much-needed improvements and patching various annoying issues.

ownCloud Desktop Client 2.2.4 is now the most advanced stable release of the open-source, free, and cross-platform software that acts as a graphical user interface for users to interact with an ownCloud server. The application is now available for all supported platforms, including GNU/Linux, Mac OS X, and Microsoft Windows.

It’s not a major update or anything, but it’s important enough for you to install it on your computer and update any of the existing versions, because it improves the Dolphin plugin for GNU/Linux users running the KDE Plasma desktop environment to use the Application name for a socket path.

The SyncEngine got some improvements as well, now allowing users to rename folders when f… (read more)

From: Softpedia