CoreOS: How to login via ssh (default password?!)

After the installation of a coreos you want to login via ssh (because of wrong localization inside your virtualbox/vmware console and no client tools installed (copy/paste not working, etc...)?
If you ask your preferred search engine, you will get many answers that there is not default password...
(Of course! The idea behind containers and container schedulers is, that everything works automatically and typing passwords does not fit in this mantra).

But no worries, only (more...)

Linux Containers – Container LInux: Core OS – a minimal linux? A quick overview: diskspace, mounts, commands, kernel, …

Virtualization techniques can be grouped into two categories
  1. os virtualization like VMware, Virtualbox, etc.
  2. container virtualization like Docker, etc.

Everybody is familiar with the first category. Creation of virtual machines is well known and most of us have created already tens or hundreds of such machines. (and deleted and lost them after some weeks). One of the benefits is, that it is easy to run additional machines on our laptops / workstations.
The second category (more...)

How to Checksum Downloads

As a DBA, in your time, you will need to download files such as Oracle binaries, patches, etc.  As a rule of thumb, you should always checksum you downloads, to ensure they are free of corruption.  In my example, I needed to download:

This is the Quarterly Full Stack Download Patch for Exadata, which is 10 zip files that (more...)

Chart Your Course With sar

The sar (system activity reporter) is a Linux utility that actually started life long ago in System V Unix.

In spite of its ancient origins, sar is still quite useful, and has even been enhanced in recent versions of Linux.

The use of sar is not limited to root – any user can run sar and its utilities.  Most Linux systems have sar installed and enabled by default to collect sar data at 10 (more...)

Disable SELinux on Oracle Linux 7

Sometimes when I want to test something or write a prototype of some sort SELinux (Security-Enhanced Linux) kicks in and hinders me, given that it is enabled by default on OL 7 UEK 4. STOP! Before I let you continue to read take a mental note of my disclaimer: I am an advocate of having … Continue reading "Disable SELinux on Oracle Linux 7"

First step to micorservices: CoreOS on virtualbox (1)

I read some articles about microservice architecture and about kubernetes / apache mesos.
My conclusion from these articles is, that lightweigt servers are a key point to this microservice architecture. Just to learn how tiny such a OS could be, i will try to install CoreOS inside virtualbox.

There is an easy way to get CoreOS running ("booting CoreOS container linux from ISO"), but there some limitations stated on the CoreOS website:

  1. There (more...)

(bash): The most useless commands (9)

After talking about
  1. rev
  2. yes
  3. sl
  4. cowsay
  5. cmatrix
  6. cal
  7. rig
here another pretty useless command:

$ pi 10
       The  pi  command  prints  100 decimal digits of Archimedes' constant pi or a number of
       digits specified by an integer parameter on the command line.

Installation of Rundeck with the Ansible plugin on Centos 7

This post shows you how to install Rundeck with the Ansible plugin on Centos 7. The installation is done with nginx as the web server and using SSL with a self signed certificate. Please read the Ansible installation script, and modify anything that should be different for your situation. You will be amazed how well readable the installation script is!

Rundeck is a web based user interface that allows you to run commands against a (more...)

How to exit of ed in SQL*Plus

I from time to time get stuck in ‘ed‘ on SQL*Plus because the editor not defined like this:

SQL> select * from duall;
select * from duall
ERROR at line 1:
ORA-00942: table or view does not exist

SQL> ed
Wrote file afiedt.buf

The Ctrl-C and Ctrl-Z, wouldn’t get you out.

The solution is simple, type ‘q‘ and press ‘Enter‘, then set editor using (more...)

Installation overview of node_exporter, prometheus and grafana

Prometheus is an open source systems monitoring and alerting toolkit originally build at Soundcloud. This blogpost shows how to install the needed components to do visualisation of linux system statistics via Grafana.

The setup consists of 3 components:
node_exporter, an exporter of system and hardware metrics.
prometheus, a metric collection and persistence layer.
grafana, the visualisation layer.

1. Preparation
The needed components are installed in the home directory of (more...)

Linux memory usage

One of the principal important configuration settings for running an Oracle database is making appropriate use of memory. Sizing the memory regions too small leads to increased IO, sizing the memory regions too big leads to inefficient use of memory and an increase in memory latency most notably because of swapping.

On Linux, there is a fair amount of memory information available, however it is not obvious how to use that information, which frequently leads (more...)

Get going with Node.js, npm and Vue.js 2 on Red Hat & Oracle Linux

A quick and rough guide on getting going with Node, npm and Vue.js 2 on a Enterprise Linux platform (Oracle Linux based on RedHat Linux)

Install Node.JS on a Oracle Enterprise Linux system:


as root:

curl –silent –location | bash –


yum -y install nodejs

(in order to disable the inaccessible proxy server that was setup for my yum environment I have to remove the line in (more...)

12.2 New Feature: the FLEX ASM disk group part 3

In the previous 2 parts of this mini series I introduced the Flex ASM disk group and two related concepts, the Quota Group and File Group. In what should have become the final part (but isn’t) I am interested in checking whether quotas are enforced.

(Un)fortunately I have uncovered a few more things that are worth investigating and blogging about, which is why a) this isn’t the last post and b) it got a bit (more...)

(bash): The most useless commands (8)

After talking about

  1. rev
  2. yes
  3. sl
  4. cowsay
  5. cmatrix
  6. cal
 i found another funny command:
Its manpage tells the following:
       Rig  is a utility that will piece together a random first name, last name, street num‐
       ber and address, along with a geographically consistant (ie, they all match  the  same
       area) city, state, ZIP code, and area code.

       It is suitable for such applications as feeding the NY times registration (more...)

Bash: enabling Eclipse for Bash Programming | Plugin basheclipse (debugging) part 1

In my last posting i showed how to install the plugin shelled and its configuration options.

Now the next step is to install basheclipse, which enables eclipse in conjunction with shelled to debug bash scripts.

Step 1: Download basheclipse

Step 2: Do not copy the jar file to the plugins directory if you are using Eclipse Neon. Copy them to the dropins directory.

Step 3: Restart eclipse (and wait. I had to wait nearly 5 (more...)

12.2 New Feature: the FLEX ASM disk group part 2

In the first part of this series I explained the basics and some potential motivation behind the use of ASM Flex disk groups. In this part I would like to complete the description of new concepts.

New Concepts related to FLEX ASM Disk Groups

With the Flex disk group mounted, the next steps are to create a few new entities. First, I want to create a Quota Group. The Quota Group – as the name (more...)

Bash: enabling Eclipse for Bash Programming | Plugin Shelled (shell editor)

After writing several posts about useless shell commands i tried to enable Eclipse for working with the bourne again shell.

First step is to get a plugin for syntax highlighting. The plugin shelled
is very easy to find. Just download the zip

and in Eclipse go to "help --> install new software".
There you have to add the archive:
And all other clicks are straight forward:

After the installation of the plugin you (more...)

Postgresql block internals, part 3

This is the third part in a series of blogposts about how postgresql manages data in its blocks (called ‘pages’ in postgres speak). If you found this post and did not read the previous ones, it might be beneficial to read block internals (part 1) and block internals, part 2 first. In these blogposts I’ve shown how heap and index pages look like, and how these can be investigated, including looking at the raw block (more...)

12.2 New Feature: the FLEX ASM disk group part 1

I knew about the 12.2 FLEX ASM disk group type from other presenters but until now – when researching the feature for the upcoming DOAG HA Day – I haven’t been able to appreciate how cool this is. And I really think it is pretty cool and worth sharing! There is a lot to be said about the feature and these tests, which is why I am splitting it into multiple parts.

Please be (more...)

Postgresql block internals, part 2

This is the second part of a blogpost about Postgresql database block internals. If you found this blogpost, and are interested in getting started with it, please read the first part, and then continue with this post.
I am doing the investigations on Oracle Linux 7u3 with postgres 9.6 (both the latest versions when this blogpost was written).

In the first part I talked about the pageinspect extension, and investigated the page header (more...)