Simple-systemd.md

Starting simple with 'systemd'

It has been said that users of modern Linux systems should be using systemd when they want to run a script as a daemon. I've always been a bit edgy when it comes to systemd, but I have to admit there may be some wisdom in this statement. So let's try something simple to start:

1. Here's a script which is appropriately named. Save this file in your home directory as donaught.sh, and then do: chmod 755 donaught.sh.

   #!/usr/bin/env bash
   # donaught.sh is my $0
   # example systemd unit that does nothing
   declare -i i=0
   while true
   do
      ((i++))
      printf '%s\n' "$(basename $0) ain't doin nuthin; $i; $(date +"%F %T.%3N")" >> /home/pi/donaught.log
      sleep 300
      if [ $i -gt 288 ]; then
          > /home/pi/donaught.log
          i=0
      fi
   done

2. Next, create a "unit file" for using donaught.sh with systemd. In your editor, create this, and save it as /etc/systemd/system/donaught.service :

   [Unit]
   Description=donaught service
   After=network-online.target
    
   [Service]
   ExecStart=/home/pi/donaught.sh
   
   [Install]
   WantedBy=multi-user.target
   

3. Finally, use systemctl (p/o systemd) to start and stop the donaught service:

   sudo systemctl start donaught
   # you can watch donaught "in action" using tail -f donaught.log
   # and when you get tired of that, just stop it
   sudo systemctl stop donaught

4. If you want the service to start at boot time, enter this command from the terminal:

   sudo systemctl enable donaught 
   
   # to prevent the service from starting at the next boot:
   sudo systemctl disable donaught

That's it for now; we'll try to find something more interesting soon. Perhaps something with libgpiod.