hostapd-dfs-checker

Check hostapd managed WLAN DFS status and trigger interface reboot when DFS brings down the interface. Compatible on OpenWrt.

This script write a pid file for checking concurrent running instances, so it's safe to call it from crontab.

Usage

Modify the code to best suit your needs. Things which you should definitely configure:

1. send_web_request function and URL, TOKEN value to implement your own notification method. The one I am using: ttimasdf/wework-webhook: Push notification through webhook to Wechat Work application
2. Check the interface name, which is currently hard coded to wlan0 (and radio0), the 802.11a WLAN interface on my router.
3. install bash if you are using OpenWrt. Busybox ash is untested. If your router has insufficient storage for packages, maybe you should change a router 😉
4. install a crontab entry for this script with crontab -e

   * * * * * /root/cron-wlan0-dfs.sh

It's done!

log messages print out both to stdout and openwrt system log. If you are using other log systems, modify the log function as needed.

LLM prompts used to assist in making this project

The raw result from LLM is omitted for conciseness. I've also add some minor changes before final releasing.

Write a bash script for a cron job following these requirements:

1. The script check the output of hostapd_cli -i wlan0 status and check for its state. store the state in /var/run/wlan0-last-state file.
2. read the last state before storing state, if state is changing, notify the state change by curl -v https://webhook.com/wework/appid/text -H "X-WW-Auth: $token" -d 'msg content'
3. if the state changes from ENABLED something else, like DFS or DISABLED, restart the WiFi by /sbin/wifi up radio0. and monitor the state once per second for 2 minutes, notify state changes inside this time period.
4. Since this script is a one-shot running once a minute. if any previous script is still running, the subsequent script running should be skipped. the running state is maintained by a pid file /var/run/cron-wlan0-dfs.pid and the running check is done through checking the pid number. no additional lock file is needed.
5. log output should be wrapped by a helper function like:

log() {
  echo "$1"
  logger -t "wlan_checker" "$1"
}

---

Request for changes.

1. In restart_and_monitor_wifi, the send_web_request should be called only when there's state change in wlan0 interface, like maintain a variable previous_state and check with current state.
2. In send_web_request, the function should log the message content to log function.
3. In send_web_request, curl should use $HOME/root_vm.crt as trusted root certificate, and remove -v flag
4. abstract the hostapd_cli call for wlan0 check to a new function and return the state string like ENABLED DFS, and add a condition where hostapd_cli -i wlan0 status contains string like wpa_ctrl_open: No such file or directory in stderr. In this case, return the case DISABLED.