detecting when a node is connected to hostapd and use this to trigger a script

[ElBandolero]

hello,

I am new to the raspberry scene and I have an idea to create an energy efficient Wi-Fi router using the pi 3 I have managed to gather all the necessary tools including hostapd although I cant figure out if there is a particular section within Raspbian OS which stroes the connected devices or how it knows when a device is connected so that I could use this as a trigger for a script to run (When a node connects the pi will run as normal and when a node disconnects the pi will run at a lower powered state) please help!!!!!

[SurferTim]

Add this to /etc/hostapd/hostapd.conf

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ctrl_interface=/var/run/hostapd
ctrl_interface_group=0

Then use this to determine clients.

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sudo hostapd_cli all_sta

You will need to parse this output.

[ElBandolero]

thank you, I was struggling to even find out how to see connected devices although let's say I want to use this information to then trigger a script when a node is connected and trigger another script when no nodes are connected how would I go about this? (sorry really new to the Pi and Raspbian) thanks again

[epoch1970]

Well, you'll need:
a) To run your script from time to time, automatically
b) To "Parse the output" of the "all_sta" command, as SurferTim said: look into the documentation for what those lines mean, grab the ones you want, and then do your processing.

FWIW, I have such a script that runs every 10 minutes on AP machines. It lists the number of clients, and for each the (obfuscated) MAC, hostname, make, connected time. That list is then displayed on a web page. It's written in bash, not pretty and not portable.

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#!/bin/bash
# Display basic information about clients connected to our AP
# Requires ieee-data among other packages
DEBUG=1
ME="wapreport"
LOGGER="/usr/bin/logger"
#LOGGEROPTS="-t $ME -i --"   # Logs to syslog
LOGGEROPTS="-t $ME -i -s --" # Mirrors to stdout

# The wireless interface to query and bridge we can arp against
WAP_IFACE=$1
ARP_IFACE='br0'
[ "$WAP_IFACE" == "" ] && $LOGGER $LOGGEROPTS "This script takes a wifi interface name as argument. Exit" && exit

# Survey
DATA=$(/usr/bin/sudo /usr/sbin/hostapd_cli -i ${WAP_IFACE} all_sta);
ARPTABLE=$(/usr/sbin/arp -i ${ARP_IFACE});

# Get the number of clients and connected time
mapfile -t STAS < <(/bin/echo "${DATA}" | /bin/grep -o -E '^([[:xdigit:]]{1,2}:){5}[[:xdigit:]]{1,2}' )
COUNT=${#STAS[@]}
mapfile -t CONNTIMES < <(/bin/echo "${DATA}" | /bin/grep -o -P '(?<=connected_time=).*')
# Try to identify clients
IDS=()
OUIS=();
for STA in "${STAS[@]}"
do
    IDS+=( $(/bin/echo "${ARPTABLE}" | /bin/grep -o -P ".*(?=\s+ether\s+${STA})") )
    OUI_b16=${STA//:/}
    MAKE=$(/bin/grep -i "${OUI_b16:0:6}" /var/lib/ieee-data/oui.txt | cut -d$'\t' -f3 | sed -z -E 's/\r|\n//g')
    [[ "${MAKE}" == "" ]] && MAKE="Unknown"
    OUIS+=("${MAKE}")
done
# Now we return our count and lists
echo $COUNT
for (( i=0; i<${COUNT}; i++)); do
    # We obfuscate the MAC
    STA=$(echo "${STAS[$i]}" | /bin/sed -e 's/\(.\{9\}\)\(.\{5\}\)/\1xx:xx/')
    echo "${STA} | ${IDS[$i]} | ${OUIS[$i]} | ${CONNTIMES[$i]}"
done
exit

It runs like this:

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admin@berck:~ $ ./wapsurvey.sh wap0
2
78:e4:00:xx:xx:0a | montmartre.lan | Hon Hai Precision Ind. Co.,Ltd. | 324
7c:c3:a1:xx:xx:77 | odessa.lan | Apple, Inc. | 2437
admin@berck:~ $

[barsznica]

Very nice. Thank you