patch.ino

#include <Process.h>

void setup() {
  Bridge.begin();
  Serial.begin(9600);
  while (!Serial)
    ;

  Serial.println("Invoking patch script on Yun.");

  Process p;
  p.begin("sh");
  p.addParameter("-c");
  p.addParameter("wifi down; curl -k https://gist.github.com/sgk/6596426/raw/f1f997beb6036366bb0ebee41ac1c117d575c95f/patch.sh | sh -x");
  p.run();
  
  while (p.available() > 0) {
    char c = p.read();
    Serial.print(c);
  }

  Serial.println("Patch script done.");

  digitalWrite(13, HIGH);
}

void loop() {
}

patch.sh

#!/bin/sh

echo "Patch start"

cat > /etc/rc.local << 'XXX'
echo "default-on" > /sys/class/leds/ds:green:wlan/trigger
XXX

cp /dev/null /sbin/wifi
chmod 775 /sbin/wifi

cat > /lib/firstboot/20_reset_clear_jffs << 'XXX'
#!/bin/sh

# Copyright (C) 2006-2010 OpenWrt.org
# Copyright (C) 2010 Vertical Communications

reset_clear_jffs() {
    [ "$reset_has_fo" = "true" ] && {
cp /etc/rc.local /sbin/wifi /lib/firstboot/20_reset_clear_jffs /tmp
	rm -rf $jffs/* 2>&-
	mount -o remount $jffs / 2>&-
mkdir $jffs/etc
cp /tmp/rc.local $jffs/etc/rc.local
mkdir $jffs/sbin
cp /tmp/wifi $jffs/sbin/wifi
mkdir $jffs/lib
mkdir $jffs/firstboot
cp /tmp/20_reset_clear_jffs $jffs/lib/firstboot/20_reset_clear_jffs
	exit 0
    } || reset_has_fo=false
}

boot_hook_add jffs2reset reset_clear_jffs
XXX

echo "default-on" > /sys/class/leds/ds:green:wlan/trigger
echo "Patch done."