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Raspberry Pi

Login prompt when connecting USB null modem cable

File: /etc/udev/rules.d/99-ttyusb.rules

KERNEL=="ttyUSB0", ACTION=="add",\
  PROGRAM="/bin/systemctl start usb-serial-ttyUSB0.service"

File: /etc/systemd/system/usb-serial-ttyUSB0.service

[Unit]
BindTo=/dev/ttyUSB0
After=/dev/ttyUSB0.device

[Service]
Type=oneshot
TimeoutStartSec=300
ExecStart=/sbin/getty -L ttyUSB0 115200 vt100
Note
journalctl reports an error when unplugging the USB device. But it doesn’t seem to be a problem.

Disable WIFI and Bluetooth

to disable onboard WiFi and BT on Pi3 add the following to file: /boot/config.txt

dtoverlay=pi3-disable-wifi
dtoverlay=pi3-disable-bt

For pi4 you can use

dtoverlay=disable-wifi
dtoverlay=disable-bt

Disable IPv6

to disable IPv6 add the following to file: /boot/config.txt

ipv6.disable=1

Reduce write IO to SD card

Albeit there are different approaches to this I typically start by disabling logging to disk.

First disable rsyslogd

systemctl disable rsyslog

Then instruct journalctl to store it’s log in volatile memory (ram)

Edit file: /etc/systemd/journald.conf and change the line

#Storage=auto

to

Storage=volatile

Reboot for changes to take effect.

Check CPU temperature

vcgencmd measure_temp

Static IP address

Edit the file: /etc/dhcpcd/dhcpcd.conf

# Example static IP configuration:
interface eth0
static ip_address=192.168.0.10/24
static ip6_address=fd51:42f8:caae:d92e::ff/64
static routers=192.168.0.1
static domain_name_servers=192.168.0.1 8.8.8.8 fd51:42f8:caae:d92e::1

ipv6 stuff is not necessary and can be omitted.

Static IP can also be setup in /etc/network/inerfaces.d/eth0 as described in Network and IPtables Ubuntu section. Then /etc/dhcpcd.conf needs the line

denyinterfaces eth0

Enable Power Button

to enable a power button connected between GND and GPIO3 add the following to file: /boot/config.txt

dtoverlay=gpio.shutdown