Question

I have a child process which runs in a pseudo terminal. The parent process does not run as root, but the child process does, through su or sudo. Because of this it is not possible to send a signal to the child process to force it to exit. I want to force it to exit by one of these means:

• emulating a Ctrl-C.
• emulating a terminal hangup.

How do I do either of these? I already have a pty master fd, and I’ve tried something like this:

write(master, &termios.c_cc[VINTR], 1)

but it doesn’t do anything.

Answer 1

I eventually went with the following solution:

After forking, instead of exec’ing sudo immediately, I exec() a helper child process instead, which in turn forks and execs sudo and calls waitpid on it. So the process hierarchy looks like this:

original process          <---- runs as user
  |
  +-- helper process      <---- runs as user, session leader,
         |                      has own pty, in pty's foreground process group
         |
         +--- sudo        <---- runs as root

By killing the helper process, the pty does not have a foreground process anymore. This will cause the OS to send SIGHUP to the entire foreground process group, regardless of the user, so sudo is SIGHUP’ed too.