xref: /titanic_52/usr/src/cmd/svc/startd/fork.c (revision 16dd44c265271a75647fb0bb41109bb7c585a526)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 /*
22  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
23  * Use is subject to license terms.
24  */
25 
26 /*
27  * fork.c - safe forking for svc.startd
28  *
29  * fork_configd() and fork_sulogin() are related, special cases that handle the
30  * spawning of specific client processes for svc.startd.
31  */
32 
33 #include <sys/contract/process.h>
34 #include <sys/corectl.h>
35 #include <sys/ctfs.h>
36 #include <sys/stat.h>
37 #include <sys/types.h>
38 #include <sys/uio.h>
39 #include <sys/wait.h>
40 #include <assert.h>
41 #include <errno.h>
42 #include <fcntl.h>
43 #include <libcontract.h>
44 #include <libcontract_priv.h>
45 #include <libscf_priv.h>
46 #include <limits.h>
47 #include <poll.h>
48 #include <port.h>
49 #include <signal.h>
50 #include <stdarg.h>
51 #include <stdio.h>
52 #include <stdlib.h>
53 #include <string.h>
54 #include <unistd.h>
55 #include <utmpx.h>
56 #include <spawn.h>
57 
58 #include "configd_exit.h"
59 #include "protocol.h"
60 #include "startd.h"
61 
62 static	struct	utmpx	*utmpp;	/* pointer for getutxent() */
63 
64 pid_t
65 startd_fork1(int *forkerr)
66 {
67 	pid_t p;
68 
69 	/*
70 	 * prefork stack
71 	 */
72 	wait_prefork();
73 
74 	p = fork1();
75 
76 	if (p == -1 && forkerr != NULL)
77 		*forkerr = errno;
78 
79 	/*
80 	 * postfork stack
81 	 */
82 	wait_postfork(p);
83 
84 	return (p);
85 }
86 
87 /*
88  * void fork_mount(char *, char *)
89  *   Run mount(1M) with the given options and mount point.  (mount(1M) has much
90  *   hidden knowledge; it's much less correct to reimplement that logic here to
91  *   save a fork(2)/exec(2) invocation.)
92  */
93 int
94 fork_mount(char *path, char *opts)
95 {
96 	pid_t pid;
97 	uint_t tries = 0;
98 	int status;
99 
100 	for (pid = fork1(); pid == -1; pid = fork1()) {
101 		if (++tries > MAX_MOUNT_RETRIES)
102 			return (-1);
103 
104 		(void) sleep(tries);
105 	}
106 
107 	if (pid != 0) {
108 		(void) waitpid(pid, &status, 0);
109 
110 		/*
111 		 * If our mount(1M) invocation exited by peculiar means, or with
112 		 * a non-zero status, our mount likelihood is low.
113 		 */
114 		if (!WIFEXITED(status) ||
115 		    WEXITSTATUS(status) != 0)
116 			return (-1);
117 
118 		return (0);
119 	}
120 
121 	(void) execl("/sbin/mount", "mount", "-o", opts, path, NULL);
122 
123 	return (-1);
124 }
125 
126 /*
127  * pid_t fork_common(...)
128  *   Common routine used by fork_sulogin and fork_configd to fork a
129  *   process in a contract with the provided terms.  Invokes
130  *   fork_sulogin (with its no-fork argument set) on errors.
131  */
132 static pid_t
133 fork_common(const char *name, const char *svc_fmri, int retries, ctid_t *ctidp,
134     uint_t inf, uint_t crit, uint_t fatal, uint_t param, uint64_t cookie)
135 {
136 	uint_t tries = 0;
137 	int ctfd, err;
138 	pid_t pid;
139 
140 	/*
141 	 * Establish process contract terms.
142 	 */
143 	if ((ctfd = open64(CTFS_ROOT "/process/template", O_RDWR)) == -1) {
144 		fork_sulogin(B_TRUE, "Could not open process contract template "
145 		    "for %s: %s\n", name, strerror(errno));
146 		/* NOTREACHED */
147 	}
148 
149 	err = ct_tmpl_set_critical(ctfd, crit);
150 	err |= ct_pr_tmpl_set_fatal(ctfd, fatal);
151 	err |= ct_tmpl_set_informative(ctfd, inf);
152 	err |= ct_pr_tmpl_set_param(ctfd, param);
153 	err |= ct_tmpl_set_cookie(ctfd, cookie);
154 	err |= ct_pr_tmpl_set_svc_fmri(ctfd, svc_fmri);
155 	err |= ct_pr_tmpl_set_svc_aux(ctfd, name);
156 	if (err) {
157 		(void) close(ctfd);
158 		fork_sulogin(B_TRUE, "Could not set %s process contract "
159 		    "terms\n", name);
160 		/* NOTREACHED */
161 	}
162 
163 	if (err = ct_tmpl_activate(ctfd)) {
164 		(void) close(ctfd);
165 		fork_sulogin(B_TRUE, "Could not activate %s process contract "
166 		    "template: %s\n", name, strerror(err));
167 		/* NOTREACHED */
168 	}
169 
170 	/*
171 	 * Attempt to fork "retries" times.
172 	 */
173 	for (pid = fork1(); pid == -1; pid = fork1()) {
174 		if (++tries > retries) {
175 			/*
176 			 * When we exit the sulogin session, init(1M)
177 			 * will restart svc.startd(1M).
178 			 */
179 			err = errno;
180 			(void) ct_tmpl_clear(ctfd);
181 			(void) close(ctfd);
182 			fork_sulogin(B_TRUE, "Could not fork to start %s: %s\n",
183 			    name, strerror(err));
184 			/* NOTREACHED */
185 		}
186 		(void) sleep(tries);
187 	}
188 
189 	/*
190 	 * Clean up, return pid and ctid.
191 	 */
192 	if (pid != 0 && (errno = contract_latest(ctidp)) != 0)
193 		uu_die("Could not get new contract id for %s\n", name);
194 	(void) ct_tmpl_clear(ctfd);
195 	(void) close(ctfd);
196 
197 	return (pid);
198 }
199 
200 /*
201  * void fork_sulogin(boolean_t, const char *, ...)
202  *   When we are invoked with the -s flag from boot (or run into an unfixable
203  *   situation), we run a private copy of sulogin.  When the sulogin session
204  *   is ended, we continue.  This is the last fallback action for system
205  *   maintenance.
206  *
207  *   If immediate is true, fork_sulogin() executes sulogin(1M) directly, without
208  *   forking.
209  *
210  *   Because fork_sulogin() is needed potentially before we daemonize, we leave
211  *   it outside the wait_register() framework.
212  */
213 /*PRINTFLIKE2*/
214 void
215 fork_sulogin(boolean_t immediate, const char *format, ...)
216 {
217 	va_list args;
218 	int fd_console;
219 
220 	(void) printf("Requesting System Maintenance Mode\n");
221 
222 	if (!booting_to_single_user)
223 		(void) printf("(See /lib/svc/share/README for more "
224 		    "information.)\n");
225 
226 	va_start(args, format);
227 	(void) vprintf(format, args);
228 	va_end(args);
229 
230 	if (!immediate) {
231 		ctid_t	ctid;
232 		pid_t	pid;
233 
234 		pid = fork_common("sulogin", SVC_SULOGIN_FMRI,
235 		    MAX_SULOGIN_RETRIES, &ctid, CT_PR_EV_HWERR, 0,
236 		    CT_PR_EV_HWERR, CT_PR_PGRPONLY, SULOGIN_COOKIE);
237 
238 		if (pid != 0) {
239 			(void) waitpid(pid, NULL, 0);
240 			contract_abandon(ctid);
241 			return;
242 		}
243 		/* close all inherited fds */
244 		closefrom(0);
245 	} else {
246 		(void) printf("Directly executing sulogin.\n");
247 		/*
248 		 * Can't call closefrom() in this MT section
249 		 * so safely close a minimum set of fds.
250 		 */
251 		(void) close(STDIN_FILENO);
252 		(void) close(STDOUT_FILENO);
253 		(void) close(STDERR_FILENO);
254 	}
255 
256 	(void) setpgrp();
257 
258 	/* open the console for sulogin */
259 	if ((fd_console = open("/dev/console", O_RDWR)) >= 0) {
260 		if (fd_console != STDIN_FILENO)
261 			while (dup2(fd_console, STDIN_FILENO) < 0 &&
262 			    errno == EINTR)
263 				;
264 		if (fd_console != STDOUT_FILENO)
265 			while (dup2(fd_console, STDOUT_FILENO) < 0 &&
266 			    errno == EINTR)
267 				;
268 		if (fd_console != STDERR_FILENO)
269 			while (dup2(fd_console, STDERR_FILENO) < 0 &&
270 			    errno == EINTR)
271 				;
272 		if (fd_console > STDERR_FILENO)
273 			(void) close(fd_console);
274 	}
275 
276 	setutxent();
277 	while ((utmpp = getutxent()) != NULL) {
278 		if (strcmp(utmpp->ut_user, "LOGIN") != 0) {
279 			if (strcmp(utmpp->ut_line, "console") == 0) {
280 				(void) kill(utmpp->ut_pid, 9);
281 				break;
282 			}
283 		}
284 	}
285 
286 	(void) execl("/sbin/sulogin", "sulogin", NULL);
287 
288 	uu_warn("Could not exec() sulogin");
289 
290 	exit(1);
291 }
292 
293 #define	CONFIGD_PATH	"/lib/svc/bin/svc.configd"
294 
295 /*
296  * void fork_configd(int status)
297  *   We are interested in exit events (since the parent's exiting means configd
298  *   is ready to run and since the child's exiting indicates an error case) and
299  *   in empty events.  This means we have a unique template for initiating
300  *   configd.
301  */
302 void
303 fork_configd(int exitstatus)
304 {
305 	pid_t pid;
306 	ctid_t ctid = -1;
307 	int err;
308 	char path[PATH_MAX];
309 
310 	/*
311 	 * Checking the existatus for the potential failure of the
312 	 * daemonized svc.configd.  If this is not the first time
313 	 * through, but a call from the svc.configd monitoring thread
314 	 * after a failure this is the status that is expected.  Other
315 	 * failures are exposed during initialization or are fixed
316 	 * by a restart (e.g door closings).
317 	 *
318 	 * If this is on-disk database corruption it will also be
319 	 * caught by a restart but could be cleared before the restart.
320 	 *
321 	 * Or this could be internal database corruption due to a
322 	 * rogue service that needs to be cleared before restart.
323 	 */
324 	if (WEXITSTATUS(exitstatus) == CONFIGD_EXIT_DATABASE_BAD) {
325 		fork_sulogin(B_FALSE, "svc.configd exited with database "
326 		    "corrupt error after initialization of the repository\n");
327 	}
328 
329 retry:
330 	log_framework(LOG_DEBUG, "fork_configd trying to start svc.configd\n");
331 
332 	/*
333 	 * If we're retrying, we will have an old contract lying around
334 	 * from the failure.  Since we're going to be creating a new
335 	 * contract shortly, we abandon the old one now.
336 	 */
337 	if (ctid != -1)
338 		contract_abandon(ctid);
339 	ctid = -1;
340 
341 	pid = fork_common("svc.configd", SCF_SERVICE_CONFIGD,
342 	    MAX_CONFIGD_RETRIES, &ctid, 0, CT_PR_EV_EXIT, 0,
343 	    CT_PR_INHERIT | CT_PR_REGENT, CONFIGD_COOKIE);
344 
345 	if (pid != 0) {
346 		int exitstatus;
347 
348 		st->st_configd_pid = pid;
349 
350 		if (waitpid(pid, &exitstatus, 0) == -1) {
351 			fork_sulogin(B_FALSE, "waitpid on svc.configd "
352 			    "failed: %s\n", strerror(errno));
353 		} else if (WIFEXITED(exitstatus)) {
354 			char *errstr;
355 
356 			/*
357 			 * Examine exitstatus.  This will eventually get more
358 			 * complicated, as we will want to teach startd how to
359 			 * invoke configd with alternate repositories, etc.
360 			 *
361 			 * Note that exec(2) failure results in an exit status
362 			 * of 1, resulting in the default clause below.
363 			 */
364 
365 			/*
366 			 * Assign readable strings to cases we don't handle, or
367 			 * have error outcomes that cannot be eliminated.
368 			 */
369 			switch (WEXITSTATUS(exitstatus)) {
370 			case CONFIGD_EXIT_BAD_ARGS:
371 				errstr = "bad arguments";
372 				break;
373 
374 			case CONFIGD_EXIT_DATABASE_BAD:
375 				errstr = "database corrupt";
376 				break;
377 
378 			case CONFIGD_EXIT_DATABASE_LOCKED:
379 				errstr = "database locked";
380 				break;
381 			case CONFIGD_EXIT_INIT_FAILED:
382 				errstr = "initialization failure";
383 				break;
384 			case CONFIGD_EXIT_DOOR_INIT_FAILED:
385 				errstr = "door initialization failure";
386 				break;
387 			case CONFIGD_EXIT_DATABASE_INIT_FAILED:
388 				errstr = "database initialization failure";
389 				break;
390 			case CONFIGD_EXIT_NO_THREADS:
391 				errstr = "no threads available";
392 				break;
393 			case CONFIGD_EXIT_LOST_MAIN_DOOR:
394 				errstr = "lost door server attachment";
395 				break;
396 			case 1:
397 				errstr = "execution failure";
398 				break;
399 			default:
400 				errstr = "unknown error";
401 				break;
402 			}
403 
404 			/*
405 			 * Remedial actions for various configd failures.
406 			 */
407 			switch (WEXITSTATUS(exitstatus)) {
408 			case CONFIGD_EXIT_OKAY:
409 				break;
410 
411 			case CONFIGD_EXIT_DATABASE_LOCKED:
412 				/* attempt remount of / read-write */
413 				if (fs_is_read_only("/", NULL) == 1) {
414 					if (fs_remount("/") == -1)
415 						fork_sulogin(B_FALSE,
416 						    "remount of root "
417 						    "filesystem failed\n");
418 
419 					goto retry;
420 				}
421 				break;
422 
423 			default:
424 				fork_sulogin(B_FALSE, "svc.configd exited "
425 				    "with status %d (%s)\n",
426 				    WEXITSTATUS(exitstatus), errstr);
427 				goto retry;
428 			}
429 		} else if (WIFSIGNALED(exitstatus)) {
430 			char signame[SIG2STR_MAX];
431 
432 			if (sig2str(WTERMSIG(exitstatus), signame))
433 				(void) snprintf(signame, SIG2STR_MAX,
434 				    "signum %d", WTERMSIG(exitstatus));
435 
436 			fork_sulogin(B_FALSE, "svc.configd signalled:"
437 			    " %s\n", signame);
438 
439 			goto retry;
440 		} else {
441 			fork_sulogin(B_FALSE, "svc.configd non-exit "
442 			    "condition: 0x%x\n", exitstatus);
443 
444 			goto retry;
445 		}
446 
447 		/*
448 		 * Announce that we have a valid svc.configd status.
449 		 */
450 		MUTEX_LOCK(&st->st_configd_live_lock);
451 		st->st_configd_lives = 1;
452 		err = pthread_cond_broadcast(&st->st_configd_live_cv);
453 		assert(err == 0);
454 		MUTEX_UNLOCK(&st->st_configd_live_lock);
455 
456 		log_framework(LOG_DEBUG, "fork_configd broadcasts configd is "
457 		    "live\n");
458 		return;
459 	}
460 
461 	/*
462 	 * Set our per-process core file path to leave core files in
463 	 * /etc/svc/volatile directory, named after the PID to aid in debugging.
464 	 */
465 	(void) snprintf(path, sizeof (path),
466 	    "/etc/svc/volatile/core.configd.%%p");
467 
468 	(void) core_set_process_path(path, strlen(path) + 1, getpid());
469 
470 	log_framework(LOG_DEBUG, "executing svc.configd\n");
471 
472 	(void) execl(CONFIGD_PATH, CONFIGD_PATH, NULL);
473 
474 	/*
475 	 * Status code is used above to identify configd exec failure.
476 	 */
477 	exit(1);
478 }
479 
480 void *
481 fork_configd_thread(void *vctid)
482 {
483 	int fd, err;
484 	ctid_t configd_ctid = (ctid_t)vctid;
485 
486 	if (configd_ctid == -1) {
487 		log_framework(LOG_DEBUG,
488 		    "fork_configd_thread starting svc.configd\n");
489 		fork_configd(0);
490 	} else {
491 		/*
492 		 * configd_ctid is known:  we broadcast and continue.
493 		 * test contract for appropriate state by verifying that
494 		 * there is one or more processes within it?
495 		 */
496 		log_framework(LOG_DEBUG,
497 		    "fork_configd_thread accepting svc.configd with CTID %ld\n",
498 		    configd_ctid);
499 		MUTEX_LOCK(&st->st_configd_live_lock);
500 		st->st_configd_lives = 1;
501 		(void) pthread_cond_broadcast(&st->st_configd_live_cv);
502 		MUTEX_UNLOCK(&st->st_configd_live_lock);
503 	}
504 
505 	fd = open64(CTFS_ROOT "/process/pbundle", O_RDONLY);
506 	if (fd == -1)
507 		uu_die("process bundle open failed");
508 
509 	/*
510 	 * Make sure we get all events (including those generated by configd
511 	 * before this thread was started).
512 	 */
513 	err = ct_event_reset(fd);
514 	assert(err == 0);
515 
516 	for (;;) {
517 		int efd, sfd;
518 		ct_evthdl_t ev;
519 		uint32_t type;
520 		ctevid_t evid;
521 		ct_stathdl_t status;
522 		ctid_t ctid;
523 		uint64_t cookie;
524 		pid_t pid;
525 
526 		if (err = ct_event_read_critical(fd, &ev)) {
527 			assert(err != EINVAL && err != EAGAIN);
528 			log_error(LOG_WARNING,
529 			    "Error reading next contract event: %s",
530 			    strerror(err));
531 			continue;
532 		}
533 
534 		evid = ct_event_get_evid(ev);
535 		ctid = ct_event_get_ctid(ev);
536 		type = ct_event_get_type(ev);
537 
538 		/* Fetch cookie. */
539 		sfd = contract_open(ctid, "process", "status", O_RDONLY);
540 		if (sfd < 0) {
541 			ct_event_free(ev);
542 			continue;
543 		}
544 
545 		if (err = ct_status_read(sfd, CTD_COMMON, &status)) {
546 			log_framework(LOG_WARNING, "Could not get status for "
547 			    "contract %ld: %s\n", ctid, strerror(err));
548 
549 			ct_event_free(ev);
550 			startd_close(sfd);
551 			continue;
552 		}
553 
554 		cookie = ct_status_get_cookie(status);
555 
556 		ct_status_free(status);
557 
558 		startd_close(sfd);
559 
560 		/*
561 		 * Don't process events from contracts we aren't interested in.
562 		 */
563 		if (cookie != CONFIGD_COOKIE) {
564 			ct_event_free(ev);
565 			continue;
566 		}
567 
568 		if (type == CT_PR_EV_EXIT) {
569 			int exitstatus;
570 
571 			(void) ct_pr_event_get_pid(ev, &pid);
572 			(void) ct_pr_event_get_exitstatus(ev,
573 			    &exitstatus);
574 
575 			if (st->st_configd_pid != pid) {
576 				/*
577 				 * This is the child exiting, so we
578 				 * abandon the contract and restart
579 				 * configd.
580 				 */
581 				contract_abandon(ctid);
582 				fork_configd(exitstatus);
583 			}
584 		}
585 
586 		efd = contract_open(ctid, "process", "ctl", O_WRONLY);
587 		if (efd != -1) {
588 			(void) ct_ctl_ack(efd, evid);
589 			startd_close(efd);
590 		}
591 
592 		ct_event_free(ev);
593 
594 	}
595 
596 	/*NOTREACHED*/
597 	return (NULL);
598 }
599 
600 void
601 fork_rc_script(char rl, const char *arg, boolean_t wait)
602 {
603 	pid_t pid;
604 	int tmpl, err, stat;
605 	char path[20] = "/sbin/rc.", log[20] = "rc..log", timebuf[20];
606 	time_t now;
607 	struct tm ltime;
608 	size_t sz;
609 	char *pathenv;
610 	char **nenv;
611 
612 	path[8] = rl;
613 
614 	tmpl = open64(CTFS_ROOT "/process/template", O_RDWR);
615 	if (tmpl >= 0) {
616 		err = ct_tmpl_set_critical(tmpl, 0);
617 		assert(err == 0);
618 
619 		err = ct_tmpl_set_informative(tmpl, 0);
620 		assert(err == 0);
621 
622 		err = ct_pr_tmpl_set_fatal(tmpl, 0);
623 		assert(err == 0);
624 
625 		err = ct_tmpl_activate(tmpl);
626 		assert(err == 0);
627 
628 		err = close(tmpl);
629 		assert(err == 0);
630 	} else {
631 		uu_warn("Could not create contract template for %s.\n", path);
632 	}
633 
634 	pid = startd_fork1(NULL);
635 	if (pid < 0) {
636 		return;
637 	} else if (pid != 0) {
638 		/* parent */
639 		if (wait) {
640 			do
641 				err = waitpid(pid, &stat, 0);
642 			while (err != 0 && errno == EINTR)
643 				;
644 
645 			if (!WIFEXITED(stat)) {
646 				log_framework(LOG_INFO,
647 				    "%s terminated with waitpid() status %d.\n",
648 				    path, stat);
649 			} else if (WEXITSTATUS(stat) != 0) {
650 				log_framework(LOG_INFO,
651 				    "%s failed with status %d.\n", path,
652 				    WEXITSTATUS(stat));
653 			}
654 		}
655 
656 		return;
657 	}
658 
659 	/* child */
660 
661 	log[2] = rl;
662 
663 	setlog(log);
664 
665 	now = time(NULL);
666 	sz = strftime(timebuf, sizeof (timebuf), "%b %e %T",
667 	    localtime_r(&now, &ltime));
668 	assert(sz != 0);
669 
670 	(void) fprintf(stderr, "%s Executing %s %s\n", timebuf, path, arg);
671 
672 	if (rl == 'S')
673 		pathenv = "PATH=/sbin:/usr/sbin:/usr/bin";
674 	else
675 		pathenv = "PATH=/usr/sbin:/usr/bin";
676 
677 	nenv = set_smf_env(NULL, 0, pathenv, NULL, NULL);
678 
679 	(void) execle(path, path, arg, 0, nenv);
680 
681 	perror("exec");
682 	exit(0);
683 }
684 
685 extern char **environ;
686 
687 /*
688  * A local variation on system(3c) which accepts a timeout argument.  This
689  * allows us to better ensure that the system will actually shut down.
690  *
691  * gracetime specifies an amount of time in seconds which the routine must wait
692  * after the command exits, to allow for asynchronous effects (like sent
693  * signals) to take effect.  This can be zero.
694  */
695 void
696 fork_with_timeout(const char *cmd, uint_t gracetime, uint_t timeout)
697 {
698 	int err = 0;
699 	pid_t pid;
700 	char *argv[4];
701 	posix_spawnattr_t attr;
702 	posix_spawn_file_actions_t factions;
703 
704 	sigset_t mask, savemask;
705 	uint_t msec_timeout;
706 	uint_t msec_spent = 0;
707 	uint_t msec_gracetime;
708 	int status;
709 
710 	msec_timeout = timeout * 1000;
711 	msec_gracetime = gracetime * 1000;
712 
713 	/*
714 	 * See also system(3c) in libc.  This is very similar, except
715 	 * that we avoid some unneeded complexity.
716 	 */
717 	err = posix_spawnattr_init(&attr);
718 	if (err == 0)
719 		err = posix_spawnattr_setflags(&attr,
720 		    POSIX_SPAWN_SETSIGMASK | POSIX_SPAWN_SETSIGDEF |
721 		    POSIX_SPAWN_NOSIGCHLD_NP | POSIX_SPAWN_WAITPID_NP |
722 		    POSIX_SPAWN_NOEXECERR_NP);
723 
724 	/*
725 	 * We choose to close fd's above 2, a deviation from system.
726 	 */
727 	if (err == 0)
728 		err = posix_spawn_file_actions_init(&factions);
729 	if (err == 0)
730 		err = posix_spawn_file_actions_addclosefrom_np(&factions,
731 		    STDERR_FILENO + 1);
732 
733 	(void) sigemptyset(&mask);
734 	(void) sigaddset(&mask, SIGCHLD);
735 	(void) thr_sigsetmask(SIG_BLOCK, &mask, &savemask);
736 
737 	argv[0] = "/bin/sh";
738 	argv[1] = "-c";
739 	argv[2] = (char *)cmd;
740 	argv[3] = NULL;
741 
742 	if (err == 0)
743 		err = posix_spawn(&pid, "/bin/sh", &factions, &attr,
744 		    (char *const *)argv, (char *const *)environ);
745 
746 	(void) posix_spawnattr_destroy(&attr);
747 	(void) posix_spawn_file_actions_destroy(&factions);
748 
749 	if (err) {
750 		uu_warn("Failed to spawn %s: %s\n", cmd, strerror(err));
751 	} else {
752 		for (;;) {
753 			int w;
754 			w = waitpid(pid, &status, WNOHANG);
755 			if (w == -1 && errno != EINTR)
756 				break;
757 			if (w > 0) {
758 				/*
759 				 * Command succeeded, so give it gracetime
760 				 * seconds for it to have an effect.
761 				 */
762 				if (status == 0 && msec_gracetime != 0)
763 					(void) poll(NULL, 0, msec_gracetime);
764 				break;
765 			}
766 
767 			(void) poll(NULL, 0, 100);
768 			msec_spent += 100;
769 			/*
770 			 * If we timed out, kill off the process, then try to
771 			 * wait for it-- it's possible that we could accumulate
772 			 * a zombie here since we don't allow waitpid to hang,
773 			 * but it's better to let that happen and continue to
774 			 * make progress.
775 			 */
776 			if (msec_spent >= msec_timeout) {
777 				uu_warn("'%s' timed out after %d "
778 				    "seconds.  Killing.\n", cmd,
779 				    timeout);
780 				(void) kill(pid, SIGTERM);
781 				(void) poll(NULL, 0, 100);
782 				(void) kill(pid, SIGKILL);
783 				(void) poll(NULL, 0, 100);
784 				(void) waitpid(pid, &status, WNOHANG);
785 				break;
786 			}
787 		}
788 	}
789 	(void) thr_sigsetmask(SIG_BLOCK, &savemask, NULL);
790 }
791