libpid0

libpid0 is a tiny Linux PID 1 helper for C programs that need to run as init inside a FROM scratch container or as PID 1 on a bare VM.

If the current process is not PID 1, pid0_run() just calls your submain with argc/argv and returns its exit code.

If the current process is PID 1, pid0_run():

• forks a managed child process
• puts the child in its own process group
• forwards incoming signals to that child process group
• reaps adopted child processes
• sets the child's process group as the foreground group for stdin, stdout, and stderr when those file descriptors are TTYs
• exits with the managed child's exit status

Public ABI

#include <pid0/pid0.h>

static int submain(int argc, char **argv) {
  (void)argc;
  (void)argv;
  return 0;
}

int main(int argc, char **argv) {
  return pid0_run(submain, argc, argv);
}

You find the source code at https://github.com/sa6mwa/libpid0.