RHCSA Objective: Operate running systems

This lab exercise uses the Alpha Lab we have setup. The point of this lab exercise is to cover the requirements of the RHCSA objective Operate running systems.

Useful documentation

List of objectives

Boot, reboot, and shut down a system normally

  • systemctl poweroff
  • systemctl reboot

Extra information: https://askubuntu.com/questions/64995/what-is-the-difference-between-shutdown-and-poweroff-commands

Boot systems into different targets manually
Interrupt the boot process in order to gain access to a system
Identify CPU/memory intensive processes, adjust process priority with renice, and kill processes
Locate and interpret system log files and journals

  • journalctl

Access a virtual machine’s console
Start and stop virtual machines
Start, stop, and check the status of network services

  • systemctl -at service
    Show all configured services
  • systemctl start name.service
    Start a service
  • systemctl stop name.service
    Stop a service
  • systemctl restart name.service
    Restart a service
  • systemctl enable name.service
  • systemctl disable name.service
    Enable / disable a service

Securely transfer files between systems

Linux Lab Setup: ‘Alpha Lab’

This post documents the setup of our Linux lab ‘Alpha Lab’. This lab is a basic setup that focusses on basic Linux system administration.

I have used CentOs version 7 (CentOS-7-x86_64-Minimal-1611.iso) for this lab and the lab exercises but use the term RHEL7 to indicate the Linux version.

VM: E7-Router

  • Standard RHEL7 virtual machine
  • Two NICS
    • enp0s3: NAT connection ‘to the internet’
    • enp0s8: Internal network
  • During installation:
    • Configure enp0s3 for DHCP
    • Configure enp0s8 with a static IP
    • Don’t select other packages
    • Default filesystem / partition layout
    • Set timezone and configure NTP
  • After installation, update all packages, install vim and tmux (my personal preference, substitute as desired)
    • yum update -y
    • yum install -y vim-enhanced tmux
  • Create a snapshot called ‘Clean slate’ for easy rollback

VM: E7-Server1

  • Standard RHEL7 virtual machine
  • One NIC
    • enp0s3: Internal network

S3Uploader: Simple S3 upload script

For a project of mine I needed a simple script or application to upload files to an Amazon S3 bucket. I couldn’t quickly find something that scratched my itch so I wrote  a simple application called S3Uploader.

Using S3Uploader is very simple, once you have your S3 bucket and credentials configured, simply install the application using

and you can start uploading files to your bucket, for example

The code is quite simple and is actually very suitable or a beginner to learn from. You can check it out the code from the source repository on BitBucket and the PyPi package page.

Diving into the code

The most interesting bit, the actual uploading of a file happens in the s3uploader.uploader module:

It’s a very simple class that takes a path to a file and uploads it to the S3 bucket. The interesting bit here is at the beginning of the store_file method where we extract the filename from the path using the os.path.basename function.

Another interesting piece of code can be found in the s3uploader.main module where we use the argparse module to process arguments.

Creating an ArgumentParser is quite easy using the following code (bits have een removed from the original source for clarity)

The  action='store_true' flag changes our argument parsing so the parameter acts as a flag instead of variable. The bucket parameter requires a variable and the –verbose parameter gives a true or false value.

The  nargs='+'  on the file parameter enables the user to pass multiple values for our file parameter.

We can process the parameters from argparse like so

Interesting parts here is the change from the parameter name store-paths to store_paths and the fact that the file parameter is an iterable due to the nargs='+'  option.

This little application was a quick and dirty job and can be improved. I’ll save that for a later time and try and write more about it if it’s interesting.

The learning revolution

It’s been some time since the media reported about MOOCs or other online / new studying platforms. In case you haven’t been following, MOOC stands for Massive Open Online Course. With the rise of the internet and the democratization of knowledge a new frontier was breached: specialised courses are no longer restricted to universities, schools or commercial training centers. Now it is possible to learn new skills from experienced instructors in an online course, in real time, with fellow students from around the world!

But as things go on the internet, yesterdays hype is todays old news. And the same applies for MOOCs. New technology has enabled anyone to create and share video courses that have been made available at an extremely low cost and sometimes even free.

The MOOC courses of yesterday would cost you anywhere from € 10,00 to a couple of hundred euros. But platforms such as PluralSight, Lynda or TutsPlus are available at a monthly subscription cost. This cost lies somewhere around € 20,00 a month and offers you access to a course library that offers you thousands (yes, 1000’s) of courses.

I have been using PluralSight for some time now and have been really happy with the quality of the courses and the content that is available.