find wifi device

$ /sbin/iw dev
phy#0
    Interface wls3
        ifindex 3
        wdev 0x1
        addr xx:xx:xx:xx:xx:xx
        ssid xxxxxxx
        type managed
        channel 36 (5180 MHz), width: 20 MHz (no HT), center1: 5180 MHz
        txpower 15.00 dBm

scan for available N/W

$ /sbin/iwlist scan

for WPA2

install related packages

$ sudo apt install wpasupplicant

generate psk for a ssid

$ wpa_passphrase myssid
# reading passphrase from stdin
mypassphrase < input from stdin
network={
    ssid="myssid"
    #psk="mypassphrase"
    psk=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
}

add these lines to /etc/network/interface

auto wls3
iface wls3 inet dhcp
  wpa-ap-scan 1
  wpa-scan-ssid 1
  wpa-ssid myssid
  wpa-psk xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

change permission /etc/network/interface

$ chmod 600 /etc/network/interface

configure cpu governor

cpu情報の確認

cat /proc/cpuinfo

cpuクロック関連ツール導入

apt-get install cpufrequtils

現在のクロックやガバナの表示

cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq
cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq
cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_min_freq
cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

状態確認

cpufreq-info
cpufreq-info -p

ガバナの変更

cpufreq-set -g ondemand

os起動時のガバナの指定

cp -pi /usr/share/doc/cpufrequtils/examples/cpufrequtils.sample /etc/default/cpufrequtils
vi /etc/default/cpufrequtils

service cpufrequtils restart

Disable swap on raspbian buster

systemctl status dphys-swapfile

systemctl stop dphys-swapfile
systemctl is-active dphys-swapfile

systemctl disable dphys-swapfile
systemctl is-enabled dphys-swapfile

rm /var/swap

Use tmpfs

mount -t tmpfs tmpfs <mount point>

or

cat << END >> /etc/fstab
tmpfs           /tmp            tmpfs   defaults,size=256m,noatime,mode=1777  0       0
END
mount /tmp