#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>

#define LEDSYSFILE "/sys/class/leds/led1/brightness"

int main(void) {
  int fd;
  ssize_t ret;
  char buf[1024];

  snprintf(buf, sizeof(buf), "%d\n", 1);

  fd = open(LEDSYSFILE, O_RDWR);
  if (fd < 0) {
    perror("open()");
    return -errno;
  }

  ret = write(fd, buf, strlen(buf));
  printf("write() returned: %d\n", ret);

  close(fd);

  return 0;
}