Shell Script

• A shell script is a file containing one or more commands
• You could type those commands individually on the command line
• Here's the content of my first shell script:

1echo Hello World!

• We have already encountered the [echo] command in

  Command Types

• Now I have to give my file a name:
  • do not choose …

UNIX philosophy

Every operating system needs to interract with users.
The original UNIX philosophy said (among other things):
Write programs that do one thing and do it well. Write programs to work together.
This philosophy applis also to the interraction with the user, and the kernel.
In other words, the UNIX system …

About vi

• vi is a screen-oriented text editor originally created for the Unix operating system
• vi was a visual mode of the ex line editor, hence the name
• Being screen-oriented means that vi would work in a terminal you would use to connect textually to UNIX like systems (so telnet and ssh would be enough to use it) …

Let's create our own systemd service.

Our service program

• We'll use a simple bash script that endlessly outputs text into a log file:

1for (( ; ; ))
2do
3	echo "still running:" $(date)  >> /tmp/myprog.log
4	sleep 1
5done

• Save this in a file, make it executable by anyone (777) and copy to /usr/bin: …

About systemd Units

• Units are the objects that systemd knows how to manage.
• These are basically a standardized representation of system resources that can be managed by systemd
• Each unit is configured by a unit file
• Here's are some of systemd units:
  • .service: A service unit describes how to manage a service or …

About systemd

• systemd is a software suite that provides an array of system components for linux
• The primary component is a "system and service manager" – an init system used to bootstrap user space and manage user processes.
• It also provides replacements for various daemons and utilities, including: …

About System Calls

• Some operations that are executed by a process involve just the CPU and the memory.
• Mathematical computations and logical decisiones are good examples of these.
• But sometimes, the process needs to do other things, that it cannot do alone.
  For example:
  • interract with the computer hardware (e.g …