Ctrl-C 如何终止子进程? [英] How does Ctrl-C terminate a child process?

问题描述

我想了解 CTRL+C 如何终止子进程而不是父进程.我在一些脚本 shell 中看到了这种行为，例如 bash，您可以在其中启动一些长时间运行的进程，然后通过输入 CTRL-C 来终止它控制权返回到外壳.

I am trying to understand how CTRL+C terminates a child but not a parent process. I see this behavior in some script shells like bash where you can start some long-running process and then terminate it by entering CTRL-C and the control returns to the shell.

你能解释一下它是如何工作的，特别是为什么父(shell)进程没有终止?

Could you explain how does it work and in particular why isn't the parent (shell) process terminated?

shell 是否必须对 CTRL+C 事件进行一些特殊处理，如果是，它究竟是做什么的?

Does the shell have to do some special handling of CTRL+C event and if yes what exactly does it do?

推荐答案

信号默认由内核处理.旧的 Unix 系统有 15 个信号；现在他们有更多.您可以检查 (或 kill -l).CTRL+C 是名称为 SIGINT 的信号.

Signals by default are handled by the kernel. Old Unix systems had 15 signals; now they have more. You can check </usr/include/signal.h> (or kill -l). CTRL+C is the signal with name SIGINT.

处理每个信号的默认动作也在内核中定义，通常它会终止接收到信号的进程.

The default action for handling each signal is defined in the kernel too, and usually it terminates the process that received the signal.

所有信号(但SIGKILL)都可以由程序处理.

All signals (but SIGKILL) can be handled by program.

这就是shell的作用:

And this is what the shell does:

• 当 shell 在交互模式下运行时，它具有针对此模式的特殊信号处理.
• 当你运行一个程序时，例如 find，shell:
  • forks 本身
  • 并为孩子设置默认信号处理
  • 用给定的命令替换子元素(例如用 find)
  • 当你按下 CTRL+C 时，父 shell 会处理这个信号，但是子 shell 会接收到它 - 使用默认操作 - 终止.(孩子也可以实现信号处理)
  • When the shell running in interactive mode, it has a special signal handling for this mode.
  • When you run a program, for example find, the shell:
    • forks itself
    • and for the child set the default signal handling
    • replace the child with the given command (e.g. with find)
    • when you press CTRL+C, parent shell handle this signal but the child will receive it - with the default action - terminate. (the child can implement signal handling too)

    你也可以在你的 shell 脚本中trap 信号......

    You can trap signals in your shell script too...

    你也可以为你的交互式 shell 设置信号处理，尝试在你的顶部输入它~/.profile.(确保您已经登录并使用另一个终端对其进行测试 - 您可以锁定自己)

    And you can set signal handling for your interactive shell too, try enter this at the top of you ~/.profile. (Ensure than you're a already logged in and test it with another terminal - you can lock out yourself)

    trap 'echo "Dont do this"' 2
    

    现在，每次在 shell 中按 CTRL+C 时，它都会打印一条消息.不要忘记删除该行！

    Now, every time you press CTRL+C in your shell, it will print a message. Don't forget to remove the line!

    如果有兴趣，您可以在源代码 这里.

    If interested, you can check the plain old /bin/sh signal handling in the source code here.

    在上面的评论中有一些错误信息(现已删除)，所以如果有人对此感兴趣，这是一个非常好的链接 - 信号处理的工作原理.

    At the above there were some misinformations in the comments (now deleted), so if someone interested here is a very nice link - how the signal handling works.

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