Look deeply into your Linux code with these Berkeley Packet Filter (BPF) Compiler Collection (bcc) tools.

The BIRD project aims to develop a fully functional dynamic IP routing daemon primarily targeted on (but not limited to) Linux, FreeBSD and other UNIX-like systems and distributed under the GNU General Public License.

I was in Prague last month for the 2017 edition of the KVM Forum. There I gave a talk about some of the work that I’ve been doing this year to improve the qcow2 file format used by QEMU for storing disk images. The focus of my work is to make qcow2 faster and to reduce its memory requirements.

I was in Prague last month for the 2017 edition of the KVM Forum. There I gave a talk about some of the work that I’ve been doing this year to improve the qcow2 file format used by QEMU for storing disk images. The focus of my work is to make qcow2 faster and to reduce its memory requirements.

Collecting benchmark results is the first step to solving disk I/O performance problems. Unfortunately, many bug reports and performance investigations fall down at the first step because bogus benchmark data is collected. This post explains common mistakes when running disk I/O benchmarks.

Introduction

One core functionality of Bash is to manage parameters. A parameter is an entity that stores values and is referenced by a name, a number or a special symbol.

parameters referenced by a name are called variables (this also applies to arrays)
parameters referenced by a number are called positional parameters and reflect the arguments given to a shell
parameters referenced by a special symbol are auto-set parameters that have different special meanings and uses

Parameter expansion is the procedure to get the value from the referenced entity, like expanding a variable to print its value. On expansion time you can do very nasty things with the parameter or its value. These things are described here.

If you saw some parameter expansion syntax somewhere, and need to check what it can be, try the overview section below!

Arrays can be special cases for parameter expansion, every applicable description mentions arrays below. Please also see the article about arrays.

For a more technical view what a parameter is and which types exist, see the dictionary entry for "parameter".

Snabb (formerly "Snabb Switch") is a simple and fast packet networking toolkit.

We are also a grassroots community of programmers and network engineers who help each other to build and deploy new network elements. We care about practical applications and finding simpler ways to do things.

About a week ago many users may have noticed instability on our hosted ZeroTier Central. Network controllers would flicker on and off, and eventually the whole service needed to be restarted across our cluster. 500 errors and timeouts were a thing.

VXLAN is an overlay network to carry Ethernet traffic over an existing (highly available and scalable) IP network while accommodating a very large number of tenants. It is defined in RFC 7348.

Starting from Linux 3.12, the VXLAN implementation is quite complete as both multicast and unicast are supported as well as IPv6 and IPv4. Let’s explore the various methods to configure it.

The installation of the Openvswitch on Ubuntu brings an automatic integration into the boot sequence. When Ubuntu is booted, the Openvswitch is also started. Any bridge or port, which has been defined in previous sessions, is restored.
BUT: No L3 interfaces are set up, junk interfaces, which have been defined in previous sessions, are restored.

These instructions will walk you through booting Container Linux via iPXE on real or virtual hardware. By default, this will run Container Linux completely out of RAM. Container Linux can also be installed to disk.

A mininum of 1024M of RAM is required to boot Container Linux via PXE.

EnhanceIO driver is based on EnhanceIO SSD caching software product
developed by STEC Inc. EnhanceIO was derived from Facebook's open source
Flashcache project. EnhanceIO uses SSDs as cache devices for
traditional rotating hard disk drives (referred to as source volumes
throughout this document).

EnhanceIO can work with any block device, be it an entire physical
disk, an individual disk partition,  a RAIDed DAS device, a SAN volume,
a device mapper volume or a software RAID (md) device.

The source volume to SSD mapping is a set-associative mapping based on
the source volume sector number with a default set size
(aka associativity) of 512 blocks and a default block size of 4 KB.
Partial cache blocks are not used. The default value of 4 KB is chosen
because it is the common I/O block size of most storage systems.  With
these default values, each cache set is 2 MB (512 * 4 KB).  Therefore,
a 400 GB SSD will have a little less than 200,000 cache sets because a
little space is used for storing the meta data on the SSD.

EnhanceIO supports three caching modes: read-only, write-through, and
write-back and three cache replacement policies: random, FIFO, and LRU.

Read-only caching mode causes EnhanceIO to direct write IO requests only
to HDD. Read IO requests are issued to HDD and the data read from HDD is
stored on SSD. Subsequent Read requests for the same blocks are carried
out from SSD, thus reducing their latency by a substantial amount. 

In Write-through mode - reads are handled similar to Read-only mode.
Write-through mode causes EnhanceIO to write application data to both
HDD and SSD. Subsequent reads of the same data benefit because they can
be served from SSD.

Write-back improves write latency by writing application requested data
only to SSD. This data, referred to as dirty data, is copied later to
HDD asynchronously. Reads are handled similar to Read-only and
Write-through modes.

Dashcam-Testberichte, Neuigkeiten und der Testsieger:

There is now a complete Open Source tool chain for some FPGAs from Lattice Semiconductor. For a convincing video that these devices and the Open Source development tools are useful, see:

Introduction to the Open Source FPGA toolchain short or long@32c3 by Clifford Wolf

Forth on icestick by James Bowman