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 …

Traditional creation of programs

• This is also called static linking
• The old way of creating programs was by writing multiple source files (text files with program code), then translating each one (called compile), thus creating object files.
  The, link these files to create an executable file, that can be run: …

What is a process

• A process is an instance of an executing program.
• A program is a file containing a range of information that describes how to construct a process at run time:
  • Machine-language instructions: These encode the algorithm of the program.
  • Data: The program file contains values used to initialize …