CSCI 373 — 27 April

`N` things about homework

Check grades on Differentiation and Integration or the Four tasks and read the data sheets for I²C hardware study.

Periodic client

Most from what we did on Wednesday. Add calls to read the acceleramoter.

Systemd

The checking link

References

systemd Raspberry Pi
Managing services with systemd from RedHat (recommended by David Reynolds)
Running Services After the Network is up from freedesktop.org
Really geeky details and history from Pid Eins
python-systemd

Useful commands

systemctl daemon-reload
systemctl enable service
systemctl start service
systemctl status service

The problem with clients

If the network is unstable, servers just wait for connections. Clents initiate connections. Here is some code I use to make sure the network is available.

    acc_connected = False
    while not acc_connected:
        try:
            acc_conn.connect((remote_host, remote_port))
            acc_connected = True
        except socket.gaierror as msg:
            print("Unable to connect {0}".format(msg))
            time.sleep(10)

The two setups

The [Unit] and [Install] sections are the same and informed by systemd Raspberry Pi and Running Services After the Network is up.

The [Service] sections have an ExecStart statement simlar to that of systemd Raspberry Pi tutorial.

One has definitions for WorkingDirectory User which shouldn’t matter. There is a definion for StandardOuput=syslog which can be useful for getting the status.

Then there are definitions for some pretty obscure options. Here is one set.

Type=oneshot

And here is other.

Type=simple
Restart=no

You can read the man page systemd.service and see if you can figure out what this is all about.

Another approach

Someone suggested the System V approach of modifying /etc/rc.local. However, this is the time for systemd.

One more thing

There were a fair number of systemd talks related to embedded systems at All Systems Go! 2017 meeting.

N things about homework