Raspberry Pi Notes

3 minute read

These are my notes on the Raspberry Pi, model 3b.

Why hook up a screen, keyboard and mouse, if all you need is a network connection? ;-)

Use Raspberry Pi Imager

Download Raspberry Pi Imager from https://www.raspberrypi.org/software/ ↗ and run it, follow the instructions to download and transfer it onto an SD card.

Raspberry Pi Imager

Before First Boot

Mount the newly created SD card and …

$ touch /Volumes/boot/ssh

to enable SSH on boot and …

$ cat - >> /Volumes/boot/wpa_supplicant.conf
country=BE
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
	ssid="Your wireless network's SSID"
	psk="Your wireless network's password"
}

and terminate with Ctl-D.

Now you’re ready to boot and log in to your new Raspberry Pi using…

$ ssh pi@raspberrypi.local

Things to do after First Boot

Change Hostname

Edit /etc/hostname and /etc/hosts, replacing raspberrypi with the new name. Reboot or execute sudo hostname <new name>.

Add SSH public key

Add your public key to ~/.ssh/authorized_keys.

Disable Password-based Access

Edit /etc/ssh/sshd_config and look for Password-related settings and turn them off ;-)

Update

$ sudo apt-get update

Load .bashrc when .bash_profile exists

$ cat - » .bash_profile if [ -f $HOME/.bashrc ]; then . $HOME/.bashrc fi ^D

Install and make Python 3 default

$ sudo apt-get install python3-pip
$ cat - >> .bash_aliases
alias python='/usr/bin/python3'
alias pip=pip3
^D
$ . .bashrc

Freeing UART/console for applications

By default, the Pi uses its UART for its console. This means that you can’t connect external devices. To free it up do the following:

Go into the configuration tool and disable serial support: sudo raspi-config, go into 5 Interfacing Options, then select P6 Serial and acknowledge you want to disable serial.
Now, one more step is needed, because else you won’t find any serial ports: edit /boot/config.txt and add enable_uart=1.
ALSO add core_freq=250 to the same /boot/config.txt, or else the handling of the data with base its baudrate on a variable clock speed ()?!) (See http://raspberrypi.stackexchange.com/questions/45570/ ↗ for some background information).
reboot

Now, after installing e.g. screen, you can access UART using e.g. screen /dev/ttyS0.

Use it…

… to host a mobile uplink, with a Huawei E3372 LTE dongle

Start by disabling the PIN using a “normal” computer.

Currently you need to edit /lib/udev/rules.d/40-usb_modeswitch.rules and change

ATTRS{idVendor}=="12d1", ATTR{bInterfaceNumber}=="00", ATTR{bInterfaceClass}=="08", RUN+="usb_modeswitch '%b/%k'

to read

'%k'

at the end.

Reboot and afterwards, the dongle will have created eth1 with IP address 192.168.8.100 and will act as a NAT router.

… as a WiFi Access Point

$ sudo apt-get install dnsmasq hostapd

Edit /etc/dhcpcd.conf and add

denyinterfaces wlan0

Edit /etc/network/interfaces, edit wlan0 section:

allow-hotplug wlan0  
iface wlan0 inet static  
    address 172.24.1.1
    netmask 255.255.255.0
    network 172.24.1.0
    broadcast 172.24.1.255

$ sudo service dhcpcd restart
$ sudo ifdown wlan0
$ sudo ifup wlan0

Edit /etc/hostapd/hostapd.conf

interface=wlan0
driver=nl80211
ssid=<YourNetworkName>

hw_mode=g
channel=6
ieee80211n=1
wmm_enabled=1
ht_capab=[HT40][SHORT-GI-20][DSSS_CCK-40]
macaddr_acl=0

auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_key_mgmt=WPA-PSK
wpa_passphrase=<YourNetworkPassword>
rsn_pairwise=CCMP

Edit /etc/default/hostapd

DAEMON_CONF="/etc/hostapd/hostapd.conf"

Edit /etc/dnsmasq.d/dnsmasq.wlan0.conf:

interface=wlan0
listen-address=172.24.1.1
bind-interfaces
server=8.8.8.8 
domain-needed
bogus-priv
dhcp-range=172.24.1.50,172.24.1.150,12h

Edit /etc/sysctl.conf:

net.ipv4.ip_forward=1

Setup NAT rules for eth0 and wlan0 to use eth1 uplink:

sudo iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE  
sudo iptables -A FORWARD -i wlan0 -o eth1 -m state --state RELATED,ESTABLISHED -j ACCEPT  
sudo iptables -A FORWARD -i eth1 -o wlan0 -j ACCEPT 
sudo iptables -A FORWARD -i eth00 -o eth1 -m state --state RELATED,ESTABLISHED -j ACCEPT  
sudo iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT 

$ sudo sh -c "iptables-save > /etc/iptables.ipv4.nat"

Edit /etc/rc.local and add (before exit 0):

iptables-restore < /etc/iptables.ipv4.nat

$ sudo service hostapd start  
$ sudo service dnsmasq start

… as a DHCP Server (for eth0)

Edit /etc/network/interfaces

auto eth0
iface eth0 inet static
    address 192.168.0.1
    netmask 255.255.255.0

Edit /etc/dnsmasq.d/dnsmasq.eth0.conf:

interface=eth0
listen-address=192.168.0.1
bind-interfaces
server=8.8.8.8 
domain-needed
bogus-priv
dhcp-range=192.168.0.50,192.168.0.150,12h

Optionally, add to /etc/dnsmasq.d/dnsmasq.eth0.conf

dhcp-option=3
dhcp-option=6

to not have it set default router and DNS resolvement, if e.g. the host has another internet connection.

… as an audio recording + playback device using Sound Blaster Play 2

use alsamixer to set audio parameters
use sudo alsactl store to save paramters
aplay -D hwplug:1 recoding.wav

To make the Sound Blaster the only and default device:

Edit /etc/asound.conf:

pcm.!default {
    type hw
    card 1
}

ctl.!default {
    type hw           
    card 1
}

card should be the card number in aplay -l and arecord -l

To record use arecord -f cd -vv test.wav To play use aplay test.wav

Christophe VG