Developers Club geek daily blog

Certification of RHCSA: experience of preparation and delivery

2 years, 10 months ago
Recently I completed the course RedHat Rapid Track Course with Exam (RH200) and successfully handed over certification of RedHat Certified System Administrator (RHCSA). It is initial certification in a line of certifications of RedHat, and I decided that the story about preparation and delivery of this examination will be useful Habrasoobshchestva (I did not find detailed stories about it on Habré). At once I will make a reservation that before examination you sign the document which prohibits to disclose information on what was at examination, however it is not forbidden to tell what was on an official rate of preparation for this examination that I also will make.

I will leave beyond the scope a question why to receive this certification, personally I handed over because
  • my employer gave me such opportunity,
  • when monitoring vacancies on the specialty I often meet a mark that official certification will be benefit,
  • well and for own ChSV of course.

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Asterisk + Huawei E1550 or as you should not save on telephony

2 years, 10 months ago
When I one and a half years ago, being a student 4 courses of telecommunications, came to work to the company for the system administrator's position, I understood what works I will have much, and it is necessary to teach all new even more. I pushed study the background, and then began to appear on couples of times at all a month because there is a lot of work, and it was precisely more interesting than what tried to teach in University to.

The company was engaged in sales, and naturally there were many such little men who are called sales managers, and they needed to call much!

In the first day showed me the existing system of telephony. 5 gateways VoIP Audiocodes MP-202B and ten DECT of phones + separate SIP a trunk on each phone. With these phones 30 people also juggled all day. That for..., I thought and decided to deliver to Asterisk.

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PowerShell, AWS CLI and json

2 years, 10 months ago
During the work with Amazon cloud, often it is necessary to execute many routine operations through Web the console. But there is a wish to automate them.
AWS CLI, the command line interface, well for this purpose approaches. Of course, it is possible to write also the application on Scala, but in daily tasks it is better oboytsya without "heavy artillery".
The AWS commands are able to return data in different formats including in json. It is possible to use bash and jq, but there is no last in cygwin repository, and hands to set laziness. Meanwhile in PowerShell there is a fine support of json! The truth it turned out that it is not absolutely simple to use it.

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Story about msdb of 42 GB in size

2 years, 10 months ago
Recently minute was issued to look why the old test server godlessly braked … I had no relation to it, but I was overcome by sports interest to understand that is with it not so.

First of all opened Resource Monitor and looked at a total load. Process of sqlserv.exe loaded the CPU under 100% and created big disk queue which was for 300 … while value above of unit is already considered problem.

In the analysis of disk activity noticed continuous IO operations in msdb:


Looked at the msdb size:

SELECT name, size = size * 8. / 1024, space_used = FILEPROPERTY(name, 'SpaceUsed') * 8. / 1024
FROM sys.database_files

also included the hand person mode:

name         size           space_used
------------ -------------- ---------------
MSDBData     42626.000000   42410.374395
MSDBLog      459.125000     6.859375

The data file occupied 42 GB … Having taken a small break I began to understand what the reason of such unhealthy volume of msdb and how to overcome problems with server performance.

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Proxmox VE 4 installation of the root section on unsupported the soft raid1 installer

2 years, 10 months ago

Starting with version 3.6 in the Proxmox installer there was an installation option on different ZFS Raid options, but did not appear, used by many, a configuration with an arrangement of a root and storage area of disks of virtual computers on program raid an array.
On Habré and in a network there is a set of similar articles, but they are actual for version 3,6, and in version 4.0 several interesting nuances appeared. Besides in this instruction I will approach a solution of this task absolutely some other way.

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We look in looking-glass

2 years, 10 months ago
Remarkable example of network solidarity are the numerous looking-glass services allowing to glance behind the scenes of very many big and small networks around the world. It is so surprising in the modern world hidden behind one hundred security systems just like that to take and execute commands on routers being one of the most critical devices of all infrastructure of data transmission.

looking-glass version6

It is only necessary to enter the IP address or a prefix in the field and to receive in reply the routing table or trace and results of work of the utility of ping. Therefore when you understand that it is possible to enter not only addresses, but also some other characters created in intelligent commands and to receive intelligent results, there comes the stupor. There is a wish to run and shout on all corners: "Yes what is it it is necessary to prohibit immediately what for absurdity?". All this effects of the last years when safety above openness and an udobnost and on it, undoubtedly, is the reasons.

It will be a question of very popular implementation of looking-glass from and that - it is possible to receive from this service.

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As the command of engineers of Airbnb "broke" the main DB of the project for few weeks

2 years, 10 months ago
Note of the translator: On Habré and in ours told about scaling of Apache Storm in Spotify, creation of 20-and 30-gigabit connections on the Ethernet networks command of the project 45 Drives, and today it will be a question of how engineers of Aribnb were engaged in splitting the basis for data of the project.

Every year the traffic of Airbnb grows 3,5 times quicker, and its peak falls on the summer period

This year in anticipation of a summer season of travel the command on service of infrastructure of Airbnb worked over scaling of our databases hard. It was necessary for the company it will be prepared for summer peaks of loading.

Splitting certain tables into sections (partition) according to the functions executed by them and their room in separate databases was the purpose of one especially important project. This project, for certain, would demand large technical attachments, including modification at the level of applications, data transfer and full testing which would guarantee integrity of data and the minimum idle time.

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Critical vulnerability in the Grub2 loader allows to bypass password protection

2 years, 10 months ago

Researchers of safety Hector Marko (Hector Marco) and Ismael Ripoll (Ismael Ripoll) published information on the vulnerability in the popular Grub2 loader found by them 0-day which is used in the majority Linux-systems. Operation of vulnerability allows to get access to the abnormal Grub2 console in circumvention of the password. It, in turn, opens for the malefactor an opportunity carrying out the attack directed to increase of privileges in systems and access to all information.

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The detailed instruction on OpenVPN v2.3.8 on Windows server 2008R2

2 years, 10 months ago
I submit the detailed instruction on OpenVPN v2.3.8 on Windows server 2008R2 with the level of enciphering of TLS. Also all parameters will be in detail described.

Setup of the server

For a start we swing a distribution kit from officially website. We start the openvpn-install-2.3.8-I001-x86_64 installer. In components we include the following:


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Experience of testing of ScaleIO

2 years, 10 months ago

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