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Get to know your linux-system - Step 3

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In this third step of “Get To Know Your Linux-System”, we wanna examine the diskspace a system uses.

And disk space - this is the number one resource if it comes to unplanned outages.

I would say - at least one time a month - a customer of mine has a problem related to a completely filled up disk space somewhere.

… and this then leads to

  • user complains
  • services that stop working
  • and it may even lead to data loss.

Yes - this hasn’t to be a problem if we had a decent monitoring in place - but this is a completely different story.

What you will learn:

Let me show you in this lesson,

  • how to get insights into the used disk-space

… and as much important like this …

  • how to examine where - in which directories and by which files - all the disk space is consumed.
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Get to know your linux-system - Step 2

In this second step of “Get To Know Your Linux-System” you will learn more about the CPU- and memory-load of your system.

What you will get

  • We will have a look at the processes a system is currently busy with
  • You will see, how much memory a system has installed and how it is used
  • You will get the insight, if your system, is slowed down because of a memory-overload.

… and incidentally, I will show you, how you can pause a process and reactivate it later on.

So let’s start with the single command, that prepares for you most of the needed information in one single view …

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Get to know your linux-system - Step 1

In this lesson I wanna show you a command, that gives you with just two keystrokes a load of useful information about a linux system.

What you can expect

In this lessen I will talk about

  • The one command I always type in at first after logging in into a system.
  • The current time and the timezone your system is configured with
  • How to find out, if your system is currently overloaded or not
  • If there are other users active on the system and what they are doing

(Yes - linux is a multi-user environment. And therefore it’s often very useful to see, what other users are doing on the system at the time you are working there.)

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What the heck are they using xargs for?

You know how to connect two tools via stdin and stdout? Great!

  • But how about the commands that don’t read from it’s input-datastream?
  • How to interconnect commands together, that naturally won’t fit?

This is, where xargs comes into play.

And because I know your time is precious - I’ve created this really short video-training … only 7:32 min :-)

In this video you will also discover …

  • the one big philosophy you can expect from most linux-tools

  • which commands can be interconnected directly

  • and the only two parameters you need for controlling the behavior of xargs most of the time.

So sit back, watch and enjoy …

If your shell always get’s you wrong - quote the right way

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Here is another question that often comes up by my students and clients:

” … how can I solve the problem with these special-characters? The shell always gets me wrong …”

The fast and simple answer to this is: You have to quote!

… and you have to to it the right way.

But let’s start from the beginning:

As you know, there are characters at the command line, that simply has special meanings for the shell.

You use them for instance, for referencing the content of a variable (“$”)

robert@demo:~$ echo Hello $NAME

… or for redirecting a datatream to a file (“>”):

robert@demo:~$ ls -l /etc > $TEMPFILE

But everytime you wanna use these special characters without their special meaning for the shell, you have to take special care about it.

(huh - three times “special” in one sentence. this must be really special ;-) )

So instead of writing

robert@demo:~$ echo Buy this book for $9 now
Buy this book for now

you have to write something like

robert@demo:~$ echo 'Buy this book for $9 now'
Buy this book for $9 now

In this way, the shell won’t try to interprete $9 as a variable. Instead it would take the “$”-sign just like what it is: a $-sign.

This mechanism is called “quoting” and technically explained for instance in depth in the Bash-Documentation.

Let me show you, how the quoting works. And your shell never gets you wrong again … ;-)

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SSH port-forwarding from within the Google Cloud Shell

Google provides a very useful tool especially for those I’m calling “cloud workers”: the Cloud Shell. This gives you access to a linux-shell for just whatever you do usually in a linux shell - directly from your browser.

From time to time I use the cloud shell as a starting-point to connect via ssh to other systems. Recently I noticed that tcp-port-forwarding via the outgoing ssh-connections doesn’t work out of the box: When trying to establish a port-forwarding (ssh user@targethost -L 8080:127.0.0.1:8080) the following error occurs:

bind: Cannot assign requested address

… and the port-forwarding doesn’t work.

The reason for this is simple - as always as you know it: The ssh-client tries to bind to the local ipv6-port. This is not supported in the cloud shell and therefore fails.

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