spawnfrozen.c

#include <spawn.h>
#include <string.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char *argv[], char *envp[]) {
  if (argc < 2) {
    printf("usage: %s program [args...]", argv[0]);
    return 1;
  }
  int ret = 0;
  pid_t child = fork();
  if (child == 0) {
    pid_t pid;
    posix_spawnattr_t attr;
    ret = posix_spawnattr_init(&attr);
    if (ret) { perror("can't init spawnattr"); exit(ret); }
    ret = posix_spawnattr_setflags(&attr, POSIX_SPAWN_START_SUSPENDED|POSIX_SPAWN_SETEXEC);
    if (ret) { perror("can't set flags"); exit(ret); }

    ret = setsid();

    ret = posix_spawnp(&pid, argv[1], NULL, &attr, &argv[1], envp);
    // should not be reached
    printf("error: ");
    exit(ret);
  }

  if (child != -1) {
    printf("spawned: %u\n", child);
  } else {
    printf("error: %s\n", strerror(errno));
  }

  return ret;
}