Function StartChildProcess

src/backend/postmaster/postmaster.c:6069–6165

* StartChildProcess -- start an auxiliary process for the postmaster * * "type" determines what kind of child will be started. All child types * initially go to AuxiliaryProcessMain, which will handle common setup. * * Return value of StartChildProcess is subprocess' PID, or 0 if failed * to start subprocess. */

 * to start subprocess.
 */
static pid_t
StartChildProcess(AuxProcType type)
{
	pid_t		pid;
	char	   *av[10];
	int			ac = 0;
	char		typebuf[32];

	/*
	 * Set up command-line arguments for subprocess
	 */
	av[ac++] = "postgres";

#ifdef EXEC_BACKEND
	av[ac++] = "--forkboot";
	av[ac++] = NULL;			/* filled in by postmaster_forkexec */
#endif

	snprintf(typebuf, sizeof(typebuf), "-x%d", type);
	av[ac++] = typebuf;

	av[ac] = NULL;
	Assert(ac < lengthof(av));

#ifdef EXEC_BACKEND
	pid = postmaster_forkexec(ac, av);
#else							/* !EXEC_BACKEND */
	pid = fork_process();

	if (pid == 0)				/* child */
	{
		InitPostmasterChild();

		/* Close the postmaster's sockets */
		ClosePostmasterPorts(false);

		/* Release postmaster's working memory context */
		MemoryContextSwitchTo(TopMemoryContext);
		MemoryContextDelete(PostmasterContext);
		PostmasterContext = NULL;

		AuxiliaryProcessMain(ac, av);	/* does not return */
	}
#endif							/* EXEC_BACKEND */

	if (pid < 0)
	{
		/* in parent, fork failed */
		int			save_errno = errno;

		errno = save_errno;
		switch (type)
		{
			case StartupProcess:
				ereport(LOG,
						(errmsg("could not fork startup process: %m")));
				break;
			case ArchiverProcess: