# Install helper to speed up getting random numbers for encryption
rpi ~$ sudo -Es
rpi ~# apt install rng-tools

# disable classic networking
rpi ~# systemctl mask networking.service
rpi ~# systemctl mask dhcpcd.service
rpi ~# mv /etc/network/interfaces /etc/network/interfaces~
rpi ~# sed -i '1i resolvconf=NO' /etc/resolvconf.conf

# enable systemd-networkd
rpi ~# systemctl enable systemd-networkd.service
rpi ~# systemctl enable systemd-resolved.service
rpi ~# ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf

rpi ~# cat > /etc/systemd/network/08-wlan0.network <<EOF
[Match]
Name=wlan0
[Network]
Address=192.168.50.60/24
EOF

iw wlan0 set type ibss
iw wlan0 ibss join RPiNet 2412 # frequency 2412 is channel 1

rpi ~# systemctl --force --full edit ad-hoc-interface@wlan0.service

[Unit]
Description=Unprotected ad-hoc (IBSS) interface
Requires=sys-subsystem-net-devices-%i.device
After=sys-subsystem-net-devices-%i.device
Wants=network.target
Before=network.target

[Service]
Environment="SSID=IBSS-RPiNet" "FREQUENCY=2412"
Type=oneshot
RemainAfterExit=yes
ExecStartPre=/sbin/iw %I set type ibss
ExecStart=/sbin/iw %I ibss join $SSID $FREQUENCY
ExecStopPost=-/sbin/iw dev %I ibss leave
ExecStopPost=-/sbin/iw %I set type managed

[Install]
WantedBy=network.target

rpi ~# systemctl enable ad-hoc-interface@wlan0.service

rpi ~$ iw dev
rpi ~$ iw dev wlan0 link
rpi ~$ ip addr
rpi ~$ sudo iw dev wlan0 scan | grep -B8 -A3 "SSID: IBSS-RPiNet"

rpi ~$ sudo systemctl stop ad-hoc-interface@wlan0.service
rpi ~$ sudo systemctl start ad-hoc-interface@wlan0.service

rpi ~$ sudo systemctl --full edit ad-hoc-interface@wlan0.service

rpi ~$ sudo -Es
rpi ~# cat > /etc/wpa_supplicant/wpa_supplicant-wlan0.conf <<EOF
country=DE
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

ap_scan=2
network={
    ssid="IBSS-RPiNet"
    frequency=2412
    mode=1
    key_mgmt=NONE
}
EOF

1pi ~# chmod 600 /etc/wpa_supplicant/wpa_supplicant-wlan0.conf
rpi ~# systemctl enable wpa_supplicant@wlan0.service

rpi ~# systemctl edit wpa_supplicant@wlan0.service

[Service]
ExecStart=
ExecStart=/sbin/wpa_supplicant -c/etc/wpa_supplicant/wpa_supplicant-%I.conf -Dwext -i%I

rpi ~$ iw dev
rpi ~$ iw dev wlan0 link
rpi ~$ ip addr
rpi ~$ sudo iw dev wlan0 scan | grep -B8 -A3 "IBSS-RPiNet"

rpi ~$ sudo -Es
rpi ~# iw wlan0 set type ibss
rpi ~# ip link set wlan0 up
rpi ~# iw wlan0 ibss join RPiNet 2432
rpi ~# ip addr add 192.168.1.2 dev wlan0
rpi ~# ip route add 192.168.1.0/24 dev wlan0 proto kernel scope link src 192.168.1.2
rpi ~# exit

rpi ~$ # check with:
rpi ~$ iw dev
rpi ~$ iw dev wlan0 link
rpi ~$ ip addr
rpi ~$ sudo iw dev wlan1 scan | grep -B8 -A3 "SSID: RPiNet"

rpi ~$ iw dev
phy#0
        Unnamed/non-netdev interface
                wdev 0x2
                addr 86:50:89:38:f2:93
                type P2P-device
                txpower 31.00 dBm
        Interface wlan0
                ifindex 3
                wdev 0x1
                addr b8:27:eb:06:e8:8b
                type managed
                channel 34 (5170 MHz), width: 20 MHz, center1: 5170 MHz
                txpower 31.00 dBm

Jul 07 22:06:17 wpa_supplicant[262]: nl80211: Failed to set interface into IBSS mode
Jul 07 22:06:17 wpa_supplicant[262]: wlan0: Association request to the driver failed

rpi ~$ systemctl cat wpa_supplicant@wlan0.service | grep '^ExecStart='
ExecStart=/sbin/wpa_supplicant -c/etc/wpa_supplicant/wpa_supplicant-%I.conf -Dnl80211,wext -i%I

rpi ~$ zcat /usr/share/doc/wpa_supplicant/examples/wpa_supplicant.conf.gz | grep -A10 '^# IBSS/ad-hoc network with RSN'

rpi ~$ sudo -Es
rpi ~# cat > /etc/wpa_supplicant/wpa_supplicant-wlan0.conf <<EOF
country=DE
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

# use 'ap_scan=2' on all devices connected to the network
# this is unnecessary if you only want the network to be created when no other networks are available
ap_scan=2

network={
    ssid="RPiNet"
    key_mgmt=WPA-PSK
    proto=RSN
    psk="verySecretPassword"
    mode=1
    frequency=2432
    pairwise=CCMP
    group=CCMP
}
EOF

1pi ~# chmod 600 /etc/wpa_supplicant/wpa_supplicant-wlan0.conf
rpi ~# systemctl disable wpa_supplicant.service
rpi ~# systemctl enable wpa_supplicant@wlan0.service

wpa_supplicant[262]: random: Cannot read from /dev/random: Resource temporarily unavailable
wpa_supplicant[262]: random: Only 18/20 bytes of strong random data available from /dev/random
wpa_supplicant[262]: random: Not enough entropy pool available for secure operations
wpa_supplicant[262]: WPA: Not enough entropy in random pool to proceed - reject first 4-way handshake

rpi ~# apt install rng-tools

wlan0: CTRL-EVENT-EAP-FAILURE EAP authentication failed