source: MondoRescue/branches/3.3/mindi-busybox/init/init.c

Last change on this file was 3621, checked in by Bruno Cornec, 7 years ago

New 3?3 banch for incorporation of latest busybox 1.25. Changing minor version to handle potential incompatibilities.
File size: 41.2 KB
Line 
1/* vi: set sw=4 ts=4: */
2/*
3 * Mini init implementation for busybox
4 *
5 * Copyright (C) 1995, 1996 by Bruce Perens <bruce@pixar.com>.
6 * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
7 * Adjusted by so many folks, it's impossible to keep track.
8 *
9 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
10 */
11
12//config:config INIT
13//config: bool "init"
14//config: default y
15//config: select FEATURE_SYSLOG
16//config: help
17//config: init is the first program run when the system boots.
18//config:
19//config:config LINUXRC
20//config: bool "Support running init from within an initrd (not initramfs)"
21//config: default y
22//config: select FEATURE_SYSLOG
23//config: help
24//config: Legacy support for running init under the old-style initrd. Allows
25//config: the name linuxrc to act as init, and it doesn't assume init is PID 1.
26//config:
27//config: This does not apply to initramfs, which runs /init as PID 1 and
28//config: requires no special support.
29//config:
30//config:config FEATURE_USE_INITTAB
31//config: bool "Support reading an inittab file"
32//config: default y
33//config: depends on INIT || LINUXRC
34//config: help
35//config: Allow init to read an inittab file when the system boot.
36//config:
37//config:config FEATURE_KILL_REMOVED
38//config: bool "Support killing processes that have been removed from inittab"
39//config: default n
40//config: depends on FEATURE_USE_INITTAB
41//config: help
42//config: When respawn entries are removed from inittab and a SIGHUP is
43//config: sent to init, this option will make init kill the processes
44//config: that have been removed.
45//config:
46//config:config FEATURE_KILL_DELAY
47//config: int "How long to wait between TERM and KILL (0 - send TERM only)" if FEATURE_KILL_REMOVED
48//config: range 0 1024
49//config: default 0
50//config: depends on FEATURE_KILL_REMOVED
51//config: help
52//config: With nonzero setting, init sends TERM, forks, child waits N
53//config: seconds, sends KILL and exits. Setting it too high is unwise
54//config: (child will hang around for too long and could actually kill
55//config: the wrong process!)
56//config:
57//config:config FEATURE_INIT_SCTTY
58//config: bool "Run commands with leading dash with controlling tty"
59//config: default y
60//config: depends on INIT || LINUXRC
61//config: help
62//config: If this option is enabled, init will try to give a controlling
63//config: tty to any command which has leading hyphen (often it's "-/bin/sh").
64//config: More precisely, init will do "ioctl(STDIN_FILENO, TIOCSCTTY, 0)".
65//config: If device attached to STDIN_FILENO can be a ctty but is not yet
66//config: a ctty for other session, it will become this process' ctty.
67//config: This is not the traditional init behavour, but is often what you want
68//config: in an embedded system where the console is only accessed during
69//config: development or for maintenance.
70//config: NB: using cttyhack applet may work better.
71//config:
72//config:config FEATURE_INIT_SYSLOG
73//config: bool "Enable init to write to syslog"
74//config: default y
75//config: depends on INIT || LINUXRC
76//config:
77//config:config FEATURE_EXTRA_QUIET
78//config: bool "Be _extra_ quiet on boot"
79//config: default y
80//config: depends on INIT || LINUXRC
81//config: help
82//config: Prevent init from logging some messages to the console during boot.
83//config:
84//config:config FEATURE_INIT_COREDUMPS
85//config: bool "Support dumping core for child processes (debugging only)"
86//config: default y
87//config: depends on INIT || LINUXRC
88//config: help
89//config: If this option is enabled and the file /.init_enable_core
90//config: exists, then init will call setrlimit() to allow unlimited
91//config: core file sizes. If this option is disabled, processes
92//config: will not generate any core files.
93//config:
94//config:config INIT_TERMINAL_TYPE
95//config: string "Initial terminal type"
96//config: default "linux"
97//config: depends on INIT || LINUXRC
98//config: help
99//config: This is the initial value set by init for the TERM environment
100//config: variable. This variable is used by programs which make use of
101//config: extended terminal capabilities.
102//config:
103//config: Note that on Linux, init attempts to detect serial terminal and
104//config: sets TERM to "vt102" if one is found.
105//config:
106//config:config FEATURE_INIT_MODIFY_CMDLINE
107//config: bool "Modify the command-line to \"init\""
108//config: default y
109//config: depends on INIT || LINUXRC
110//config: help
111//config: When launched as PID 1 and after parsing its arguments, init
112//config: wipes all the arguments but argv[0] and rewrites argv[0] to
113//config: contain only "init", so that its command-line appears solely as
114//config: "init" in tools such as ps.
115//config: If this option is set to Y, init will keep its original behavior,
116//config: otherwise, all the arguments including argv[0] will be preserved,
117//config: be they parsed or ignored by init.
118//config: The original command-line used to launch init can then be
119//config: retrieved in /proc/1/cmdline on Linux, for example.
120
121//applet:IF_INIT(APPLET(init, BB_DIR_SBIN, BB_SUID_DROP))
122//applet:IF_LINUXRC(APPLET_ODDNAME(linuxrc, init, BB_DIR_ROOT, BB_SUID_DROP, linuxrc))
123
124//kbuild:lib-$(CONFIG_INIT) += init.o
125//kbuild:lib-$(CONFIG_LINUXRC) += init.o
126
127#define DEBUG_SEGV_HANDLER 0
128
129#include "libbb.h"
130#include <syslog.h>
131#include <sys/resource.h>
132#ifdef __linux__
133# include <linux/vt.h>
134# include <sys/sysinfo.h>
135#endif
136#include "reboot.h" /* reboot() constants */
137
138#if DEBUG_SEGV_HANDLER
139# undef _GNU_SOURCE
140# define _GNU_SOURCE 1
141# undef __USE_GNU
142# define __USE_GNU 1
143# include <execinfo.h>
144# include <sys/ucontext.h>
145#endif
146
147/* Used only for sanitizing purposes in set_sane_term() below. On systems where
148 * the baud rate is stored in a separate field, we can safely disable them. */
149#ifndef CBAUD
150# define CBAUD 0
151# define CBAUDEX 0
152#endif
153
154/* Was a CONFIG_xxx option. A lot of people were building
155 * not fully functional init by switching it on! */
156#define DEBUG_INIT 0
157
158#define CONSOLE_NAME_SIZE 32
159
160/* Default sysinit script. */
161#ifndef INIT_SCRIPT
162# define INIT_SCRIPT "/etc/init.d/rcS"
163#endif
164
165/* Each type of actions can appear many times. They will be
166 * handled in order. RESTART is an exception, only 1st is used.
167 */
168/* Start these actions first and wait for completion */
169#define SYSINIT 0x01
170/* Start these after SYSINIT and wait for completion */
171#define WAIT 0x02
172/* Start these after WAIT and *dont* wait for completion */
173#define ONCE 0x04
174/*
175 * NB: while SYSINIT/WAIT/ONCE are being processed,
176 * SIGHUP ("reread /etc/inittab") will be processed only after
177 * each group of actions. If new inittab adds, say, a SYSINIT action,
178 * it will not be run, since init is already "past SYSINIT stage".
179 */
180/* Start these after ONCE are started, restart on exit */
181#define RESPAWN 0x08
182/* Like RESPAWN, but wait for <Enter> to be pressed on tty */
183#define ASKFIRST 0x10
184/*
185 * Start these on SIGINT, and wait for completion.
186 * Then go back to respawning RESPAWN and ASKFIRST actions.
187 * NB: kernel sends SIGINT to us if Ctrl-Alt-Del was pressed.
188 */
189#define CTRLALTDEL 0x20
190/*
191 * Start these before killing all processes in preparation for
192 * running RESTART actions or doing low-level halt/reboot/poweroff
193 * (initiated by SIGUSR1/SIGTERM/SIGUSR2).
194 * Wait for completion before proceeding.
195 */
196#define SHUTDOWN 0x40
197/*
198 * exec() on SIGQUIT. SHUTDOWN actions are started and waited for,
199 * then all processes are killed, then init exec's 1st RESTART action,
200 * replacing itself by it. If no RESTART action specified,
201 * SIGQUIT has no effect.
202 */
203#define RESTART 0x80
204
205
206/* A linked list of init_actions, to be read from inittab */
207struct init_action {
208 struct init_action *next;
209 pid_t pid;
210 uint8_t action_type;
211 char terminal[CONSOLE_NAME_SIZE];
212 char command[1];
213};
214
215static struct init_action *init_action_list = NULL;
216
217static const char *log_console = VC_5;
218
219enum {
220 L_LOG = 0x1,
221 L_CONSOLE = 0x2,
222};
223
224/* Print a message to the specified device.
225 * "where" may be bitwise-or'd from L_LOG | L_CONSOLE
226 * NB: careful, we can be called after vfork!
227 */
228#define dbg_message(...) do { if (DEBUG_INIT) message(__VA_ARGS__); } while (0)
229static void message(int where, const char *fmt, ...)
230 __attribute__ ((format(printf, 2, 3)));
231static void message(int where, const char *fmt, ...)
232{
233 va_list arguments;
234 unsigned l;
235 char msg[128];
236
237 msg[0] = '\r';
238 va_start(arguments, fmt);
239 l = 1 + vsnprintf(msg + 1, sizeof(msg) - 2, fmt, arguments);
240 if (l > sizeof(msg) - 2)
241 l = sizeof(msg) - 2;
242 va_end(arguments);
243
244#if ENABLE_FEATURE_INIT_SYSLOG
245 msg[l] = '\0';
246 if (where & L_LOG) {
247 /* Log the message to syslogd */
248 openlog(applet_name, 0, LOG_DAEMON);
249 /* don't print "\r" */
250 syslog(LOG_INFO, "%s", msg + 1);
251 closelog();
252 }
253 msg[l++] = '\n';
254 msg[l] = '\0';
255#else
256 {
257 static int log_fd = -1;
258
259 msg[l++] = '\n';
260 msg[l] = '\0';
261 /* Take full control of the log tty, and never close it.
262 * It's mine, all mine! Muhahahaha! */
263 if (log_fd < 0) {
264 if (!log_console) {
265 log_fd = STDERR_FILENO;
266 } else {
267 log_fd = device_open(log_console, O_WRONLY | O_NONBLOCK | O_NOCTTY);
268 if (log_fd < 0) {
269 bb_error_msg("can't log to %s", log_console);
270 where = L_CONSOLE;
271 } else {
272 close_on_exec_on(log_fd);
273 }
274 }
275 }
276 if (where & L_LOG) {
277 full_write(log_fd, msg, l);
278 if (log_fd == STDERR_FILENO)
279 return; /* don't print dup messages */
280 }
281 }
282#endif
283
284 if (where & L_CONSOLE) {
285 /* Send console messages to console so people will see them. */
286 full_write(STDERR_FILENO, msg, l);
287 }
288}
289
290static void console_init(void)
291{
292#ifdef VT_OPENQRY
293 int vtno;
294#endif
295 char *s;
296
297 s = getenv("CONSOLE");
298 if (!s)
299 s = getenv("console");
300 if (s) {
301 int fd = open(s, O_RDWR | O_NONBLOCK | O_NOCTTY);
302 if (fd >= 0) {
303 dup2(fd, STDIN_FILENO);
304 dup2(fd, STDOUT_FILENO);
305 xmove_fd(fd, STDERR_FILENO);
306 }
307 dbg_message(L_LOG, "console='%s'", s);
308 } else {
309 /* Make sure fd 0,1,2 are not closed
310 * (so that they won't be used by future opens) */
311 bb_sanitize_stdio();
312// Users report problems
313// /* Make sure init can't be blocked by writing to stderr */
314// fcntl(STDERR_FILENO, F_SETFL, fcntl(STDERR_FILENO, F_GETFL) | O_NONBLOCK);
315 }
316
317 s = getenv("TERM");
318#ifdef VT_OPENQRY
319 if (ioctl(STDIN_FILENO, VT_OPENQRY, &vtno) != 0) {
320 /* Not a linux terminal, probably serial console.
321 * Force the TERM setting to vt102
322 * if TERM is set to linux (the default) */
323 if (!s || strcmp(s, "linux") == 0)
324 putenv((char*)"TERM=vt102");
325 if (!ENABLE_FEATURE_INIT_SYSLOG)
326 log_console = NULL;
327 } else
328#endif
329 if (!s)
330 putenv((char*)"TERM=" CONFIG_INIT_TERMINAL_TYPE);
331}
332
333/* Set terminal settings to reasonable defaults.
334 * NB: careful, we can be called after vfork! */
335static void set_sane_term(void)
336{
337 struct termios tty;
338
339 tcgetattr(STDIN_FILENO, &tty);
340
341 /* set control chars */
342 tty.c_cc[VINTR] = 3; /* C-c */
343 tty.c_cc[VQUIT] = 28; /* C-\ */
344 tty.c_cc[VERASE] = 127; /* C-? */
345 tty.c_cc[VKILL] = 21; /* C-u */
346 tty.c_cc[VEOF] = 4; /* C-d */
347 tty.c_cc[VSTART] = 17; /* C-q */
348 tty.c_cc[VSTOP] = 19; /* C-s */
349 tty.c_cc[VSUSP] = 26; /* C-z */
350
351#ifdef __linux__
352 /* use line discipline 0 */
353 tty.c_line = 0;
354#endif
355
356 /* Make it be sane */
357#ifndef CRTSCTS
358# define CRTSCTS 0
359#endif
360 /* added CRTSCTS to fix Debian bug 528560 */
361 tty.c_cflag &= CBAUD | CBAUDEX | CSIZE | CSTOPB | PARENB | PARODD | CRTSCTS;
362 tty.c_cflag |= CREAD | HUPCL | CLOCAL;
363
364 /* input modes */
365 tty.c_iflag = ICRNL | IXON | IXOFF;
366
367 /* output modes */
368 tty.c_oflag = OPOST | ONLCR;
369
370 /* local modes */
371 tty.c_lflag = ISIG | ICANON | ECHO | ECHOE | ECHOK | ECHOCTL | ECHOKE | IEXTEN;
372
373 tcsetattr_stdin_TCSANOW(&tty);
374}
375
376/* Open the new terminal device.
377 * NB: careful, we can be called after vfork! */
378static int open_stdio_to_tty(const char* tty_name)
379{
380 /* empty tty_name means "use init's tty", else... */
381 if (tty_name[0]) {
382 int fd;
383
384 close(STDIN_FILENO);
385 /* fd can be only < 0 or 0: */
386 fd = device_open(tty_name, O_RDWR);
387 if (fd) {
388 message(L_LOG | L_CONSOLE, "can't open %s: %s",
389 tty_name, strerror(errno));
390 return 0; /* failure */
391 }
392 dup2(STDIN_FILENO, STDOUT_FILENO);
393 dup2(STDIN_FILENO, STDERR_FILENO);
394 }
395 set_sane_term();
396 return 1; /* success */
397}
398
399static void reset_sighandlers_and_unblock_sigs(void)
400{
401 bb_signals(0
402 + (1 << SIGUSR1)
403 + (1 << SIGUSR2)
404 + (1 << SIGTERM)
405 + (1 << SIGQUIT)
406 + (1 << SIGINT)
407 + (1 << SIGHUP)
408 + (1 << SIGTSTP)
409 + (1 << SIGSTOP)
410 , SIG_DFL);
411 sigprocmask_allsigs(SIG_UNBLOCK);
412}
413
414/* Wrapper around exec:
415 * Takes string.
416 * If chars like '>' detected, execs '[-]/bin/sh -c "exec ......."'.
417 * Otherwise splits words on whitespace, deals with leading dash,
418 * and uses plain exec().
419 * NB: careful, we can be called after vfork!
420 */
421static void init_exec(const char *command)
422{
423 /* +8 allows to write VLA sizes below more efficiently: */
424 unsigned command_size = strlen(command) + 8;
425 /* strlen(command) + strlen("exec ")+1: */
426 char buf[command_size];
427 /* strlen(command) / 2 + 4: */
428 char *cmd[command_size / 2];
429 int dash;
430
431 dash = (command[0] == '-' /* maybe? && command[1] == '/' */);
432 command += dash;
433
434 /* See if any special /bin/sh requiring characters are present */
435 if (strpbrk(command, "~`!$^&*()=|\\{}[];\"'<>?") != NULL) {
436 sprintf(buf, "exec %s", command); /* excluding "-" */
437 /* NB: LIBBB_DEFAULT_LOGIN_SHELL define has leading dash */
438 cmd[0] = (char*)(LIBBB_DEFAULT_LOGIN_SHELL + !dash);
439 cmd[1] = (char*)"-c";
440 cmd[2] = buf;
441 cmd[3] = NULL;
442 command = LIBBB_DEFAULT_LOGIN_SHELL + 1;
443 } else {
444 /* Convert command (char*) into cmd (char**, one word per string) */
445 char *word, *next;
446 int i = 0;
447 next = strcpy(buf, command - dash); /* command including "-" */
448 command = next + dash;
449 while ((word = strsep(&next, " \t")) != NULL) {
450 if (*word != '\0') { /* not two spaces/tabs together? */
451 cmd[i] = word;
452 i++;
453 }
454 }
455 cmd[i] = NULL;
456 }
457 /* If we saw leading "-", it is interactive shell.
458 * Try harder to give it a controlling tty.
459 */
460 if (ENABLE_FEATURE_INIT_SCTTY && dash) {
461 /* _Attempt_ to make stdin a controlling tty. */
462 ioctl(STDIN_FILENO, TIOCSCTTY, 0 /*only try, don't steal*/);
463 }
464 /* Here command never contains the dash, cmd[0] might */
465 BB_EXECVP(command, cmd);
466 message(L_LOG | L_CONSOLE, "can't run '%s': %s", command, strerror(errno));
467 /* returns if execvp fails */
468}
469
470/* Used only by run_actions */
471static pid_t run(const struct init_action *a)
472{
473 pid_t pid;
474
475 /* Careful: don't be affected by a signal in vforked child */
476 sigprocmask_allsigs(SIG_BLOCK);
477 if (BB_MMU && (a->action_type & ASKFIRST))
478 pid = fork();
479 else
480 pid = vfork();
481 if (pid < 0)
482 message(L_LOG | L_CONSOLE, "can't fork");
483 if (pid) {
484 sigprocmask_allsigs(SIG_UNBLOCK);
485 return pid; /* Parent or error */
486 }
487
488 /* Child */
489
490 /* Reset signal handlers that were set by the parent process */
491 reset_sighandlers_and_unblock_sigs();
492
493 /* Create a new session and make ourself the process group leader */
494 setsid();
495
496 /* Open the new terminal device */
497 if (!open_stdio_to_tty(a->terminal))
498 _exit(EXIT_FAILURE);
499
500 /* NB: on NOMMU we can't wait for input in child, so
501 * "askfirst" will work the same as "respawn". */
502 if (BB_MMU && (a->action_type & ASKFIRST)) {
503 static const char press_enter[] ALIGN1 =
504#ifdef CUSTOMIZED_BANNER
505#include CUSTOMIZED_BANNER
506#endif
507 "\nPlease press Enter to activate this console. ";
508 char c;
509 /*
510 * Save memory by not exec-ing anything large (like a shell)
511 * before the user wants it. This is critical if swap is not
512 * enabled and the system has low memory. Generally this will
513 * be run on the second virtual console, and the first will
514 * be allowed to start a shell or whatever an init script
515 * specifies.
516 */
517 dbg_message(L_LOG, "waiting for enter to start '%s'"
518 "(pid %d, tty '%s')\n",
519 a->command, getpid(), a->terminal);
520 full_write(STDOUT_FILENO, press_enter, sizeof(press_enter) - 1);
521 while (safe_read(STDIN_FILENO, &c, 1) == 1 && c != '\n')
522 continue;
523 }
524
525 /*
526 * When a file named /.init_enable_core exists, setrlimit is called
527 * before processes are spawned to set core file size as unlimited.
528 * This is for debugging only. Don't use this is production, unless
529 * you want core dumps lying about....
530 */
531 if (ENABLE_FEATURE_INIT_COREDUMPS) {
532 if (access("/.init_enable_core", F_OK) == 0) {
533 struct rlimit limit;
534 limit.rlim_cur = RLIM_INFINITY;
535 limit.rlim_max = RLIM_INFINITY;
536 setrlimit(RLIMIT_CORE, &limit);
537 }
538 }
539
540 /* Log the process name and args */
541 message(L_LOG, "starting pid %d, tty '%s': '%s'",
542 getpid(), a->terminal, a->command);
543
544 /* Now run it. The new program will take over this PID,
545 * so nothing further in init.c should be run. */
546 init_exec(a->command);
547 /* We're still here? Some error happened. */
548 _exit(-1);
549}
550
551static struct init_action *mark_terminated(pid_t pid)
552{
553 struct init_action *a;
554
555 if (pid > 0) {
556 update_utmp_DEAD_PROCESS(pid);
557 for (a = init_action_list; a; a = a->next) {
558 if (a->pid == pid) {
559 a->pid = 0;
560 return a;
561 }
562 }
563 }
564 return NULL;
565}
566
567static void waitfor(pid_t pid)
568{
569 /* waitfor(run(x)): protect against failed fork inside run() */
570 if (pid <= 0)
571 return;
572
573 /* Wait for any child (prevent zombies from exiting orphaned processes)
574 * but exit the loop only when specified one has exited. */
575 while (1) {
576 pid_t wpid = wait(NULL);
577 mark_terminated(wpid);
578 /* Unsafe. SIGTSTP handler might have wait'ed it already */
579 /*if (wpid == pid) break;*/
580 /* More reliable: */
581 if (kill(pid, 0))
582 break;
583 }
584}
585
586/* Run all commands of a particular type */
587static void run_actions(int action_type)
588{
589 struct init_action *a;
590
591 for (a = init_action_list; a; a = a->next) {
592 if (!(a->action_type & action_type))
593 continue;
594
595 if (a->action_type & (SYSINIT | WAIT | ONCE | CTRLALTDEL | SHUTDOWN)) {
596 pid_t pid = run(a);
597 if (a->action_type & (SYSINIT | WAIT | CTRLALTDEL | SHUTDOWN))
598 waitfor(pid);
599 }
600 if (a->action_type & (RESPAWN | ASKFIRST)) {
601 /* Only run stuff with pid == 0. If pid != 0,
602 * it is already running
603 */
604 if (a->pid == 0)
605 a->pid = run(a);
606 }
607 }
608}
609
610static void new_init_action(uint8_t action_type, const char *command, const char *cons)
611{
612 struct init_action *a, **nextp;
613
614 /* Scenario:
615 * old inittab:
616 * ::shutdown:umount -a -r
617 * ::shutdown:swapoff -a
618 * new inittab:
619 * ::shutdown:swapoff -a
620 * ::shutdown:umount -a -r
621 * On reload, we must ensure entries end up in correct order.
622 * To achieve that, if we find a matching entry, we move it
623 * to the end.
624 */
625 nextp = &init_action_list;
626 while ((a = *nextp) != NULL) {
627 /* Don't enter action if it's already in the list.
628 * This prevents losing running RESPAWNs.
629 */
630 if (strcmp(a->command, command) == 0
631 && strcmp(a->terminal, cons) == 0
632 ) {
633 /* Remove from list */
634 *nextp = a->next;
635 /* Find the end of the list */
636 while (*nextp != NULL)
637 nextp = &(*nextp)->next;
638 a->next = NULL;
639 goto append;
640 }
641 nextp = &a->next;
642 }
643
644 a = xzalloc(sizeof(*a) + strlen(command));
645
646 /* Append to the end of the list */
647 append:
648 *nextp = a;
649 a->action_type = action_type;
650 strcpy(a->command, command);
651 safe_strncpy(a->terminal, cons, sizeof(a->terminal));
652 dbg_message(L_LOG | L_CONSOLE, "command='%s' action=%x tty='%s'\n",
653 a->command, a->action_type, a->terminal);
654}
655
656/* NOTE that if CONFIG_FEATURE_USE_INITTAB is NOT defined,
657 * then parse_inittab() simply adds in some default
658 * actions (i.e., runs INIT_SCRIPT and then starts a pair
659 * of "askfirst" shells). If CONFIG_FEATURE_USE_INITTAB
660 * _is_ defined, but /etc/inittab is missing, this
661 * results in the same set of default behaviors.
662 */
663static void parse_inittab(void)
664{
665#if ENABLE_FEATURE_USE_INITTAB
666 char *token[4];
667 parser_t *parser = config_open2("/etc/inittab", fopen_for_read);
668
669 if (parser == NULL)
670#endif
671 {
672 /* No inittab file - set up some default behavior */
673 /* Sysinit */
674 new_init_action(SYSINIT, INIT_SCRIPT, "");
675 /* Askfirst shell on tty1-4 */
676 new_init_action(ASKFIRST, bb_default_login_shell, "");
677//TODO: VC_1 instead of ""? "" is console -> ctty problems -> angry users
678 new_init_action(ASKFIRST, bb_default_login_shell, VC_2);
679 new_init_action(ASKFIRST, bb_default_login_shell, VC_3);
680 new_init_action(ASKFIRST, bb_default_login_shell, VC_4);
681 /* Reboot on Ctrl-Alt-Del */
682 new_init_action(CTRLALTDEL, "reboot", "");
683 /* Umount all filesystems on halt/reboot */
684 new_init_action(SHUTDOWN, "umount -a -r", "");
685 /* Swapoff on halt/reboot */
686 new_init_action(SHUTDOWN, "swapoff -a", "");
687 /* Restart init when a QUIT is received */
688 new_init_action(RESTART, "init", "");
689 return;
690 }
691
692#if ENABLE_FEATURE_USE_INITTAB
693 /* optional_tty:ignored_runlevel:action:command
694 * Delims are not to be collapsed and need exactly 4 tokens
695 */
696 while (config_read(parser, token, 4, 0, "#:",
697 PARSE_NORMAL & ~(PARSE_TRIM | PARSE_COLLAPSE))) {
698 /* order must correspond to SYSINIT..RESTART constants */
699 static const char actions[] ALIGN1 =
700 "sysinit\0""wait\0""once\0""respawn\0""askfirst\0"
701 "ctrlaltdel\0""shutdown\0""restart\0";
702 int action;
703 char *tty = token[0];
704
705 if (!token[3]) /* less than 4 tokens */
706 goto bad_entry;
707 action = index_in_strings(actions, token[2]);
708 if (action < 0 || !token[3][0]) /* token[3]: command */
709 goto bad_entry;
710 /* turn .*TTY -> /dev/TTY */
711 if (tty[0]) {
712 tty = concat_path_file("/dev/", skip_dev_pfx(tty));
713 }
714 new_init_action(1 << action, token[3], tty);
715 if (tty[0])
716 free(tty);
717 continue;
718 bad_entry:
719 message(L_LOG | L_CONSOLE, "Bad inittab entry at line %d",
720 parser->lineno);
721 }
722 config_close(parser);
723#endif
724}
725
726static void pause_and_low_level_reboot(unsigned magic) NORETURN;
727static void pause_and_low_level_reboot(unsigned magic)
728{
729 pid_t pid;
730
731 /* Allow time for last message to reach serial console, etc */
732 sleep(1);
733
734 /* We have to fork here, since the kernel calls do_exit(EXIT_SUCCESS)
735 * in linux/kernel/sys.c, which can cause the machine to panic when
736 * the init process exits... */
737 pid = vfork();
738 if (pid == 0) { /* child */
739 reboot(magic);
740 _exit(EXIT_SUCCESS);
741 }
742 while (1)
743 sleep(1);
744}
745
746static void run_shutdown_and_kill_processes(void)
747{
748 /* Run everything to be run at "shutdown". This is done _prior_
749 * to killing everything, in case people wish to use scripts to
750 * shut things down gracefully... */
751 run_actions(SHUTDOWN);
752
753 message(L_CONSOLE | L_LOG, "The system is going down NOW!");
754
755 /* Send signals to every process _except_ pid 1 */
756 kill(-1, SIGTERM);
757 message(L_CONSOLE | L_LOG, "Sent SIG%s to all processes", "TERM");
758 sync();
759 sleep(1);
760
761 kill(-1, SIGKILL);
762 message(L_CONSOLE, "Sent SIG%s to all processes", "KILL");
763 sync();
764 /*sleep(1); - callers take care about making a pause */
765}
766
767/* Signal handling by init:
768 *
769 * For process with PID==1, on entry kernel sets all signals to SIG_DFL
770 * and unmasks all signals. However, for process with PID==1,
771 * default action (SIG_DFL) on any signal is to ignore it,
772 * even for special signals SIGKILL and SIGCONT.
773 * Also, any signal can be caught or blocked.
774 * (but SIGSTOP is still handled specially, at least in 2.6.20)
775 *
776 * We install two kinds of handlers, "immediate" and "delayed".
777 *
778 * Immediate handlers execute at any time, even while, say, sysinit
779 * is running.
780 *
781 * Delayed handlers just set a flag variable. The variable is checked
782 * in the main loop and acted upon.
783 *
784 * halt/poweroff/reboot and restart have immediate handlers.
785 * They only traverse linked list of struct action's, never modify it,
786 * this should be safe to do even in signal handler. Also they
787 * never return.
788 *
789 * SIGSTOP and SIGTSTP have immediate handlers. They just wait
790 * for SIGCONT to happen.
791 *
792 * SIGHUP has a delayed handler, because modifying linked list
793 * of struct action's from a signal handler while it is manipulated
794 * by the program may be disastrous.
795 *
796 * Ctrl-Alt-Del has a delayed handler. Not a must, but allowing
797 * it to happen even somewhere inside "sysinit" would be a bit awkward.
798 *
799 * There is a tiny probability that SIGHUP and Ctrl-Alt-Del will collide
800 * and only one will be remembered and acted upon.
801 */
802
803/* The SIGPWR/SIGUSR[12]/SIGTERM handler */
804static void halt_reboot_pwoff(int sig) NORETURN;
805static void halt_reboot_pwoff(int sig)
806{
807 const char *m;
808 unsigned rb;
809
810 /* We may call run() and it unmasks signals,
811 * including the one masked inside this signal handler.
812 * Testcase which would start multiple reboot scripts:
813 * while true; do reboot; done
814 * Preventing it:
815 */
816 reset_sighandlers_and_unblock_sigs();
817
818 run_shutdown_and_kill_processes();
819
820 m = "halt";
821 rb = RB_HALT_SYSTEM;
822 if (sig == SIGTERM) {
823 m = "reboot";
824 rb = RB_AUTOBOOT;
825 } else if (sig == SIGUSR2) {
826 m = "poweroff";
827 rb = RB_POWER_OFF;
828 }
829 message(L_CONSOLE, "Requesting system %s", m);
830 pause_and_low_level_reboot(rb);
831 /* not reached */
832}
833
834/* Handler for QUIT - exec "restart" action,
835 * else (no such action defined) do nothing */
836static void exec_restart_action(void)
837{
838 struct init_action *a;
839
840 for (a = init_action_list; a; a = a->next) {
841 if (!(a->action_type & RESTART))
842 continue;
843
844 /* Starting from here, we won't return.
845 * Thus don't need to worry about preserving errno
846 * and such.
847 */
848
849 reset_sighandlers_and_unblock_sigs();
850
851 run_shutdown_and_kill_processes();
852
853#ifdef RB_ENABLE_CAD
854 /* Allow Ctrl-Alt-Del to reboot the system.
855 * This is how kernel sets it up for init, we follow suit.
856 */
857 reboot(RB_ENABLE_CAD); /* misnomer */
858#endif
859
860 if (open_stdio_to_tty(a->terminal)) {
861 dbg_message(L_CONSOLE, "Trying to re-exec %s", a->command);
862 /* Theoretically should be safe.
863 * But in practice, kernel bugs may leave
864 * unkillable processes, and wait() may block forever.
865 * Oh well. Hoping "new" init won't be too surprised
866 * by having children it didn't create.
867 */
868 //while (wait(NULL) > 0)
869 // continue;
870 init_exec(a->command);
871 }
872 /* Open or exec failed */
873 pause_and_low_level_reboot(RB_HALT_SYSTEM);
874 /* not reached */
875 }
876}
877
878/* The SIGSTOP/SIGTSTP handler
879 * NB: inside it, all signals except SIGCONT are masked
880 * via appropriate setup in sigaction().
881 */
882static void stop_handler(int sig UNUSED_PARAM)
883{
884 smallint saved_bb_got_signal;
885 int saved_errno;
886
887 saved_bb_got_signal = bb_got_signal;
888 saved_errno = errno;
889 signal(SIGCONT, record_signo);
890
891 while (1) {
892 pid_t wpid;
893
894 if (bb_got_signal == SIGCONT)
895 break;
896 /* NB: this can accidentally wait() for a process
897 * which we waitfor() elsewhere! waitfor() must have
898 * code which is resilient against this.
899 */
900 wpid = wait_any_nohang(NULL);
901 mark_terminated(wpid);
902 sleep(1);
903 }
904
905 signal(SIGCONT, SIG_DFL);
906 errno = saved_errno;
907 bb_got_signal = saved_bb_got_signal;
908}
909
910#if ENABLE_FEATURE_USE_INITTAB
911static void reload_inittab(void)
912{
913 struct init_action *a, **nextp;
914
915 message(L_LOG, "reloading /etc/inittab");
916
917 /* Disable old entries */
918 for (a = init_action_list; a; a = a->next)
919 a->action_type = 0;
920
921 /* Append new entries, or modify existing entries
922 * (incl. setting a->action_type) if cmd and device name
923 * match new ones. End result: only entries with
924 * a->action_type == 0 are stale.
925 */
926 parse_inittab();
927
928#if ENABLE_FEATURE_KILL_REMOVED
929 /* Kill stale entries */
930 /* Be nice and send SIGTERM first */
931 for (a = init_action_list; a; a = a->next)
932 if (a->action_type == 0 && a->pid != 0)
933 kill(a->pid, SIGTERM);
934 if (CONFIG_FEATURE_KILL_DELAY) {
935 /* NB: parent will wait in NOMMU case */
936 if ((BB_MMU ? fork() : vfork()) == 0) { /* child */
937 sleep(CONFIG_FEATURE_KILL_DELAY);
938 for (a = init_action_list; a; a = a->next)
939 if (a->action_type == 0 && a->pid != 0)
940 kill(a->pid, SIGKILL);
941 _exit(EXIT_SUCCESS);
942 }
943 }
944#endif
945
946 /* Remove stale entries and SYSINIT entries.
947 * We never rerun SYSINIT entries anyway,
948 * removing them too saves a few bytes
949 */
950 nextp = &init_action_list;
951 while ((a = *nextp) != NULL) {
952 /*
953 * Why pid == 0 check?
954 * Process can be removed from inittab and added *later*.
955 * If we delete its entry but process still runs,
956 * duplicate is spawned when the entry is re-added.
957 */
958 if ((a->action_type & ~SYSINIT) == 0 && a->pid == 0) {
959 *nextp = a->next;
960 free(a);
961 } else {
962 nextp = &a->next;
963 }
964 }
965
966 /* Not needed: */
967 /* run_actions(RESPAWN | ASKFIRST); */
968 /* - we return to main loop, which does this automagically */
969}
970#endif
971
972static int check_delayed_sigs(void)
973{
974 int sigs_seen = 0;
975
976 while (1) {
977 smallint sig = bb_got_signal;
978
979 if (!sig)
980 return sigs_seen;
981 bb_got_signal = 0;
982 sigs_seen = 1;
983#if ENABLE_FEATURE_USE_INITTAB
984 if (sig == SIGHUP)
985 reload_inittab();
986#endif
987 if (sig == SIGINT)
988 run_actions(CTRLALTDEL);
989 if (sig == SIGQUIT) {
990 exec_restart_action();
991 /* returns only if no restart action defined */
992 }
993 if ((1 << sig) & (0
994#ifdef SIGPWR
995 + (1 << SIGPWR)
996#endif
997 + (1 << SIGUSR1)
998 + (1 << SIGUSR2)
999 + (1 << SIGTERM)
1000 )) {
1001 halt_reboot_pwoff(sig);
1002 }
1003 }
1004}
1005
1006#if DEBUG_SEGV_HANDLER
1007static
1008void handle_sigsegv(int sig, siginfo_t *info, void *ucontext)
1009{
1010 long ip;
1011 ucontext_t *uc;
1012
1013 uc = ucontext;
1014 ip = uc->uc_mcontext.gregs[REG_EIP];
1015 fdprintf(2, "signal:%d address:0x%lx ip:0x%lx\n",
1016 sig,
1017 /* this is void*, but using %p would print "(null)"
1018 * even for ptrs which are not exactly 0, but, say, 0x123:
1019 */
1020 (long)info->si_addr,
1021 ip);
1022 {
1023 /* glibc extension */
1024 void *array[50];
1025 int size;
1026 size = backtrace(array, 50);
1027 backtrace_symbols_fd(array, size, 2);
1028 }
1029 for (;;) sleep(9999);
1030}
1031#endif
1032
1033static void sleep_much(void)
1034{
1035 sleep(30 * 24*60*60);
1036}
1037
1038int init_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
1039int init_main(int argc UNUSED_PARAM, char **argv)
1040{
1041 if (argv[1] && strcmp(argv[1], "-q") == 0) {
1042 return kill(1, SIGHUP);
1043 }
1044
1045#if DEBUG_SEGV_HANDLER
1046 {
1047 struct sigaction sa;
1048 memset(&sa, 0, sizeof(sa));
1049 sa.sa_sigaction = handle_sigsegv;
1050 sa.sa_flags = SA_SIGINFO;
1051 sigaction(SIGSEGV, &sa, NULL);
1052 sigaction(SIGILL, &sa, NULL);
1053 sigaction(SIGFPE, &sa, NULL);
1054 sigaction(SIGBUS, &sa, NULL);
1055 }
1056#endif
1057
1058 if (!DEBUG_INIT) {
1059 /* Expect to be invoked as init with PID=1 or be invoked as linuxrc */
1060 if (getpid() != 1
1061 && (!ENABLE_LINUXRC || applet_name[0] != 'l') /* not linuxrc? */
1062 ) {
1063 bb_error_msg_and_die("must be run as PID 1");
1064 }
1065#ifdef RB_DISABLE_CAD
1066 /* Turn off rebooting via CTL-ALT-DEL - we get a
1067 * SIGINT on CAD so we can shut things down gracefully... */
1068 reboot(RB_DISABLE_CAD); /* misnomer */
1069#endif
1070 }
1071
1072 /* If, say, xmalloc would ever die, we don't want to oops kernel
1073 * by exiting.
1074 * NB: we set die_func *after* PID 1 check and bb_show_usage.
1075 * Otherwise, for example, "init u" ("please rexec yourself"
1076 * command for sysvinit) will show help text (which isn't too bad),
1077 * *and sleep forever* (which is bad!)
1078 */
1079 die_func = sleep_much;
1080
1081 /* Figure out where the default console should be */
1082 console_init();
1083 set_sane_term();
1084 xchdir("/");
1085 setsid();
1086
1087 /* Make sure environs is set to something sane */
1088 putenv((char *) "HOME=/");
1089 putenv((char *) bb_PATH_root_path);
1090 putenv((char *) "SHELL=/bin/sh");
1091 putenv((char *) "USER=root"); /* needed? why? */
1092
1093 if (argv[1])
1094 xsetenv("RUNLEVEL", argv[1]);
1095
1096#if !ENABLE_FEATURE_EXTRA_QUIET
1097 /* Hello world */
1098 message(L_CONSOLE | L_LOG, "init started: %s", bb_banner);
1099#endif
1100
1101#if 0
1102/* It's 2013, does anyone really still depend on this? */
1103/* If you do, consider adding swapon to sysinit actions then! */
1104/* struct sysinfo is linux-specific */
1105# ifdef __linux__
1106 /* Make sure there is enough memory to do something useful. */
1107 /*if (ENABLE_SWAPONOFF) - WRONG: we may have non-bbox swapon*/ {
1108 struct sysinfo info;
1109
1110 if (sysinfo(&info) == 0
1111 && (info.mem_unit ? info.mem_unit : 1) * (long long)info.totalram < 1024*1024
1112 ) {
1113 message(L_CONSOLE, "Low memory, forcing swapon");
1114 /* swapon -a requires /proc typically */
1115 new_init_action(SYSINIT, "mount -t proc proc /proc", "");
1116 /* Try to turn on swap */
1117 new_init_action(SYSINIT, "swapon -a", "");
1118 run_actions(SYSINIT); /* wait and removing */
1119 }
1120 }
1121# endif
1122#endif
1123
1124 /* Check if we are supposed to be in single user mode */
1125 if (argv[1]
1126 && (strcmp(argv[1], "single") == 0 || strcmp(argv[1], "-s") == 0 || LONE_CHAR(argv[1], '1'))
1127 ) {
1128 /* ??? shouldn't we set RUNLEVEL="b" here? */
1129 /* Start a shell on console */
1130 new_init_action(RESPAWN, bb_default_login_shell, "");
1131 } else {
1132 /* Not in single user mode - see what inittab says */
1133
1134 /* NOTE that if CONFIG_FEATURE_USE_INITTAB is NOT defined,
1135 * then parse_inittab() simply adds in some default
1136 * actions (i.e., INIT_SCRIPT and a pair
1137 * of "askfirst" shells) */
1138 parse_inittab();
1139 }
1140
1141#if ENABLE_SELINUX
1142 if (getenv("SELINUX_INIT") == NULL) {
1143 int enforce = 0;
1144
1145 putenv((char*)"SELINUX_INIT=YES");
1146 if (selinux_init_load_policy(&enforce) == 0) {
1147 BB_EXECVP(argv[0], argv);
1148 } else if (enforce > 0) {
1149 /* SELinux in enforcing mode but load_policy failed */
1150 message(L_CONSOLE, "can't load SELinux Policy. "
1151 "Machine is in enforcing mode. Halting now.");
1152 return EXIT_FAILURE;
1153 }
1154 }
1155#endif
1156
1157 if (ENABLE_FEATURE_INIT_MODIFY_CMDLINE) {
1158 /* Make the command line just say "init" - that's all, nothing else */
1159 strncpy(argv[0], "init", strlen(argv[0]));
1160 /* Wipe argv[1]-argv[N] so they don't clutter the ps listing */
1161 while (*++argv)
1162 nuke_str(*argv);
1163 }
1164
1165 /* Set up signal handlers */
1166 if (!DEBUG_INIT) {
1167 struct sigaction sa;
1168
1169 /* Stop handler must allow only SIGCONT inside itself */
1170 memset(&sa, 0, sizeof(sa));
1171 sigfillset(&sa.sa_mask);
1172 sigdelset(&sa.sa_mask, SIGCONT);
1173 sa.sa_handler = stop_handler;
1174 /* NB: sa_flags doesn't have SA_RESTART.
1175 * It must be able to interrupt wait().
1176 */
1177 sigaction_set(SIGTSTP, &sa); /* pause */
1178 /* Does not work as intended, at least in 2.6.20.
1179 * SIGSTOP is simply ignored by init:
1180 */
1181 sigaction_set(SIGSTOP, &sa); /* pause */
1182
1183 /* These signals must interrupt wait(),
1184 * setting handler without SA_RESTART flag.
1185 */
1186 bb_signals_recursive_norestart(0
1187 + (1 << SIGINT) /* Ctrl-Alt-Del */
1188 + (1 << SIGQUIT) /* re-exec another init */
1189#ifdef SIGPWR
1190 + (1 << SIGPWR) /* halt */
1191#endif
1192 + (1 << SIGUSR1) /* halt */
1193 + (1 << SIGTERM) /* reboot */
1194 + (1 << SIGUSR2) /* poweroff */
1195#if ENABLE_FEATURE_USE_INITTAB
1196 + (1 << SIGHUP) /* reread /etc/inittab */
1197#endif
1198 , record_signo);
1199 }
1200
1201 /* Now run everything that needs to be run */
1202 /* First run the sysinit command */
1203 run_actions(SYSINIT);
1204 check_delayed_sigs();
1205 /* Next run anything that wants to block */
1206 run_actions(WAIT);
1207 check_delayed_sigs();
1208 /* Next run anything to be run only once */
1209 run_actions(ONCE);
1210
1211 /* Now run the looping stuff for the rest of forever.
1212 */
1213 while (1) {
1214 int maybe_WNOHANG;
1215
1216 maybe_WNOHANG = check_delayed_sigs();
1217
1218 /* (Re)run the respawn/askfirst stuff */
1219 run_actions(RESPAWN | ASKFIRST);
1220 maybe_WNOHANG |= check_delayed_sigs();
1221
1222 /* Don't consume all CPU time - sleep a bit */
1223 sleep(1);
1224 maybe_WNOHANG |= check_delayed_sigs();
1225
1226 /* Wait for any child process(es) to exit.
1227 *
1228 * If check_delayed_sigs above reported that a signal
1229 * was caught, wait will be nonblocking. This ensures
1230 * that if SIGHUP has reloaded inittab, respawn and askfirst
1231 * actions will not be delayed until next child death.
1232 */
1233 if (maybe_WNOHANG)
1234 maybe_WNOHANG = WNOHANG;
1235 while (1) {
1236 pid_t wpid;
1237 struct init_action *a;
1238
1239 /* If signals happen _in_ the wait, they interrupt it,
1240 * bb_signals_recursive_norestart set them up that way
1241 */
1242 wpid = waitpid(-1, NULL, maybe_WNOHANG);
1243 if (wpid <= 0)
1244 break;
1245
1246 a = mark_terminated(wpid);
1247 if (a) {
1248 message(L_LOG, "process '%s' (pid %d) exited. "
1249 "Scheduling for restart.",
1250 a->command, wpid);
1251 }
1252 /* See if anyone else is waiting to be reaped */
1253 maybe_WNOHANG = WNOHANG;
1254 }
1255 } /* while (1) */
1256}
1257
1258//usage:#define linuxrc_trivial_usage NOUSAGE_STR
1259//usage:#define linuxrc_full_usage ""
1260
1261//usage:#define init_trivial_usage
1262//usage: ""
1263//usage:#define init_full_usage "\n\n"
1264//usage: "Init is the first process started during boot. It never exits."
1265//usage: IF_FEATURE_USE_INITTAB(
1266//usage: "\n""It (re)spawns children according to /etc/inittab."
1267//usage: )
1268//usage: IF_NOT_FEATURE_USE_INITTAB(
1269//usage: "\n""This version of init doesn't use /etc/inittab,"
1270//usage: "\n""has fixed set of processed to run."
1271//usage: )
1272//usage:
1273//usage:#define init_notes_usage
1274//usage: "This version of init is designed to be run only by the kernel.\n"
1275//usage: "\n"
1276//usage: "BusyBox init doesn't support multiple runlevels. The runlevels field of\n"
1277//usage: "the /etc/inittab file is completely ignored by BusyBox init. If you want\n"
1278//usage: "runlevels, use sysvinit.\n"
1279//usage: "\n"
1280//usage: "BusyBox init works just fine without an inittab. If no inittab is found,\n"
1281//usage: "it has the following default behavior:\n"
1282//usage: "\n"
1283//usage: " ::sysinit:/etc/init.d/rcS\n"
1284//usage: " ::askfirst:/bin/sh\n"
1285//usage: " ::ctrlaltdel:/sbin/reboot\n"
1286//usage: " ::shutdown:/sbin/swapoff -a\n"
1287//usage: " ::shutdown:/bin/umount -a -r\n"
1288//usage: " ::restart:/sbin/init\n"
1289//usage: " tty2::askfirst:/bin/sh\n"
1290//usage: " tty3::askfirst:/bin/sh\n"
1291//usage: " tty4::askfirst:/bin/sh\n"
1292//usage: "\n"
1293//usage: "If you choose to use an /etc/inittab file, the inittab entry format is as follows:\n"
1294//usage: "\n"
1295//usage: " <id>:<runlevels>:<action>:<process>\n"
1296//usage: "\n"
1297//usage: " <id>:\n"
1298//usage: "\n"
1299//usage: " WARNING: This field has a non-traditional meaning for BusyBox init!\n"
1300//usage: " The id field is used by BusyBox init to specify the controlling tty for\n"
1301//usage: " the specified process to run on. The contents of this field are\n"
1302//usage: " appended to \"/dev/\" and used as-is. There is no need for this field to\n"
1303//usage: " be unique, although if it isn't you may have strange results. If this\n"
1304//usage: " field is left blank, then the init's stdin/out will be used.\n"
1305//usage: "\n"
1306//usage: " <runlevels>:\n"
1307//usage: "\n"
1308//usage: " The runlevels field is completely ignored.\n"
1309//usage: "\n"
1310//usage: " <action>:\n"
1311//usage: "\n"
1312//usage: " Valid actions include: sysinit, respawn, askfirst, wait,\n"
1313//usage: " once, restart, ctrlaltdel, and shutdown.\n"
1314//usage: "\n"
1315//usage: " The available actions can be classified into two groups: actions\n"
1316//usage: " that are run only once, and actions that are re-run when the specified\n"
1317//usage: " process exits.\n"
1318//usage: "\n"
1319//usage: " Run only-once actions:\n"
1320//usage: "\n"
1321//usage: " 'sysinit' is the first item run on boot. init waits until all\n"
1322//usage: " sysinit actions are completed before continuing. Following the\n"
1323//usage: " completion of all sysinit actions, all 'wait' actions are run.\n"
1324//usage: " 'wait' actions, like 'sysinit' actions, cause init to wait until\n"
1325//usage: " the specified task completes. 'once' actions are asynchronous,\n"
1326//usage: " therefore, init does not wait for them to complete. 'restart' is\n"
1327//usage: " the action taken to restart the init process. By default this should\n"
1328//usage: " simply run /sbin/init, but can be a script which runs pivot_root or it\n"
1329//usage: " can do all sorts of other interesting things. The 'ctrlaltdel' init\n"
1330//usage: " actions are run when the system detects that someone on the system\n"
1331//usage: " console has pressed the CTRL-ALT-DEL key combination. Typically one\n"
1332//usage: " wants to run 'reboot' at this point to cause the system to reboot.\n"
1333//usage: " Finally the 'shutdown' action specifies the actions to taken when\n"
1334//usage: " init is told to reboot. Unmounting filesystems and disabling swap\n"
1335//usage: " is a very good here.\n"
1336//usage: "\n"
1337//usage: " Run repeatedly actions:\n"
1338//usage: "\n"
1339//usage: " 'respawn' actions are run after the 'once' actions. When a process\n"
1340//usage: " started with a 'respawn' action exits, init automatically restarts\n"
1341//usage: " it. Unlike sysvinit, BusyBox init does not stop processes from\n"
1342//usage: " respawning out of control. The 'askfirst' actions acts just like\n"
1343//usage: " respawn, except that before running the specified process it\n"
1344//usage: " displays the line \"Please press Enter to activate this console.\"\n"
1345//usage: " and then waits for the user to press enter before starting the\n"
1346//usage: " specified process.\n"
1347//usage: "\n"
1348//usage: " Unrecognized actions (like initdefault) will cause init to emit an\n"
1349//usage: " error message, and then go along with its business. All actions are\n"
1350//usage: " run in the order they appear in /etc/inittab.\n"
1351//usage: "\n"
1352//usage: " <process>:\n"
1353//usage: "\n"
1354//usage: " Specifies the process to be executed and its command line.\n"
1355//usage: "\n"
1356//usage: "Example /etc/inittab file:\n"
1357//usage: "\n"
1358//usage: " # This is run first except when booting in single-user mode\n"
1359//usage: " #\n"
1360//usage: " ::sysinit:/etc/init.d/rcS\n"
1361//usage: " \n"
1362//usage: " # /bin/sh invocations on selected ttys\n"
1363//usage: " #\n"
1364//usage: " # Start an \"askfirst\" shell on the console (whatever that may be)\n"
1365//usage: " ::askfirst:-/bin/sh\n"
1366//usage: " # Start an \"askfirst\" shell on /dev/tty2-4\n"
1367//usage: " tty2::askfirst:-/bin/sh\n"
1368//usage: " tty3::askfirst:-/bin/sh\n"
1369//usage: " tty4::askfirst:-/bin/sh\n"
1370//usage: " \n"
1371//usage: " # /sbin/getty invocations for selected ttys\n"
1372//usage: " #\n"
1373//usage: " tty4::respawn:/sbin/getty 38400 tty4\n"
1374//usage: " tty5::respawn:/sbin/getty 38400 tty5\n"
1375//usage: " \n"
1376//usage: " \n"
1377//usage: " # Example of how to put a getty on a serial line (for a terminal)\n"
1378//usage: " #\n"
1379//usage: " #::respawn:/sbin/getty -L ttyS0 9600 vt100\n"
1380//usage: " #::respawn:/sbin/getty -L ttyS1 9600 vt100\n"
1381//usage: " #\n"
1382//usage: " # Example how to put a getty on a modem line\n"
1383//usage: " #::respawn:/sbin/getty 57600 ttyS2\n"
1384//usage: " \n"
1385//usage: " # Stuff to do when restarting the init process\n"
1386//usage: " ::restart:/sbin/init\n"
1387//usage: " \n"
1388//usage: " # Stuff to do before rebooting\n"
1389//usage: " ::ctrlaltdel:/sbin/reboot\n"
1390//usage: " ::shutdown:/bin/umount -a -r\n"
1391//usage: " ::shutdown:/sbin/swapoff -a\n"
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