信号就是软件中断，可以向正在执行的程序(进程)发送有关异步事件发生的信息。
Signals are software interrupts that send information about an occurrence of an asynchronous event to an executing program, or process.
一旦驱动程序接收到坐标，它就将有关触摸和任何可用数据的信号发送给用户应用程序，并将数据发送给应用程序(如果可能的话)。
Once the driver receives the coordinates, it signals the user applications about the touch and the availability of any data, and sends the applications the data (if that is possible).
配套的实用程序pkill接受pgrep的所有选项和一个信号，它把这个信号发送给与给定的条件匹配的所有进程。
A companion utility, pkill, takes all the options of pgrep and accepts a signal to send to all processes that match the given criteria.
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