System Sleep States

When you put your computer to suspend, it will turn some of its devices to power saving mode to preserve energy consumption. But computers have many sleep states from deeper to shallow just like humans. The most shallow one is the freeze (or S0-idle) which only puts CPU to idle and if possible turn other … Continue reading System Sleep States →

Physical Host Metrics in Ceilometer – An Openstack Liberty Tale

This post is about the errors while getting physical machine metrics with ceilometer specifically Openstack Liberty. Simply errors can be: - No metrics shown in: ceilometer meter-list specifically metrics listed below: compute.node.cpu.frequency compute.node.cpu.idle.percent compute.node.cpu.idle.time compute.node.cpu.iowait.percent compute.node.cpu.iowait.time compute.node.cpu.kernel.percent compute.node.cpu.kernel.time compute.node.cpu.percent compute.node.cpu.user.time - No samples in: ceilometer sample-list --meter compute.node.cpu.* where * is the metrics mentioned above. - … Continue reading Physical Host Metrics in Ceilometer – An Openstack Liberty Tale →

SysReq, Raising Elephants Is So Utterly Boring

SysRq keyboard key is very magical. You can perform a safe reboot a locked up computer with this key. To achieve this remember mnemonics: "Raising Elephants Is So Utterly Boring" To use SysRq: Press Alt and SysRq (Print Screen) keys at the same time (but do NOT release them) While holding Alt and SysRq keys … Continue reading SysReq, Raising Elephants Is So Utterly Boring →

Reclaim empty space from, Shrink disk of qcow2 disk file

To reclaim disk space (in other words to shrink disk space) of qcow2 disk file you need to run following steps. 1. Fill guest disk with empty file This is required since disk does not really hold its configured size, instead it has a sparse file format in creation time. After a while disk gets … Continue reading Reclaim empty space from, Shrink disk of qcow2 disk file →

Singleton Design Pattern

Singleton design pattern is well known design pattern which uses a single object to access its methods at all time. Assume that you have a configuration file to read settings from. You are expecting to access various settings from different source files. With singleton you'll hold a single object in memory and use this object … Continue reading Singleton Design Pattern →

Agile Manifesto

Scrum has been used by Google since 2005. Scrum is widely used agile framework. In short Agile can be described with the following manifesto: Individuals and interactions,over,processes and tools Working software,over,comprehensive documentation Customer collaboration,over,contract negotiation Responding to change,over,following a plan Hats off for this manifesto. look at: agilemanifesto.org for details.

Search packages in debian based distros

You are probably familiar with: apt-get install <package-name> command to install new packages to your debian based distro. You can easily search for a package from command line with the following command: apt-cache search <package-name> if you are not completely know package name get little help from grep and pipe (|) combinations. For example if … Continue reading Search packages in debian based distros →

KVM Offline Backups

I use KVM in my production servers. But there are some critical questions with KVM usage. Backup process of running virtual machines may be top most question of KVM users. Although, there are many other solutions in the literature, I will discuss more defensive method in this article. Before I move on to details of … Continue reading KVM Offline Backups →

Soket Programlama – 1

İstemci Sunucu Kavramı ve Örnek Tasarımlar Soket programlama IPC (interprocess communication) mimarisinde sıklıkla tercih edilen metotlardandır. Pek çok uygulama bu kavramı kullanmaktadır. En basitinden internet üzerinden oynanan bir tavla uygulaması soket programlama kullanılarak yapılabilir. Soket programlama için temel iki kavram olan istemci ve sunucuyu açıklayalım. İstemciden çok sayıda olabilir. Sunucudan bir tane olacaktır. Aslında bu … Continue reading Soket Programlama – 1 →

Soket Programlama – 2

Basit bir Sunucu Yapalım Bu yazımızda basit bir sunucu yazılımı yapacağız. Bunu temel bazı kavramları yeri geldikçe açıklayarak yapalım. Beklentilerinizin aksine malesef bu sunucu multi-threaded değil single threaded olacaktır. Bu yöntemin seçilmesinin sebebi, asıl amaç olan istemci-sunucu kavramına odaklanılması içindir. Multi-threading kavramını başka bir yazımız için planlayıp konumuza dönelim. Soket (socket) nedir? Soket aslında iki … Continue reading Soket Programlama – 2 →