There's no guaranty that a single call to `Write` will suffice to write all of the Pid.  Arguably it will, but it's still bad practice.

Also, consider:

```go
pidBytes := []byte(strconv.Itoa(os.Getpid()))
err := ioutil.WriteFile("brog.pid", pidBytes, 0770)
if err != nil {
    return fmt.Errorf("writing pid to file, %v", err)
}
return nil
```