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//config:config INIT 12//config: bool "init (9.3 kb)" 13//config: default y 14//config: select FEATURE_SYSLOG 15//config: help 16//config: init is the first program run when the system boots. 17//config: 18//config:config LINUXRC 19//config: bool "linuxrc: support running init from initrd (not initramfs)" 20//config: default y 21//config: select FEATURE_SYSLOG 22//config: help 23//config: Legacy support for running init under the old-style initrd. Allows 24//config: the name linuxrc to act as init, and it doesn't assume init is PID 1. 25//config: 26//config: This does not apply to initramfs, which runs /init as PID 1 and 27//config: requires no special support. 28//config: 29//config:config FEATURE_USE_INITTAB 30//config: bool "Support reading an inittab file" 31//config: default y 32//config: depends on INIT || LINUXRC 33//config: help 34//config: Allow init to read an inittab file when the system boot. 35//config: 36//config:config FEATURE_KILL_REMOVED 37//config: bool "Support killing processes that have been removed from inittab" 38//config: default n 39//config: depends on FEATURE_USE_INITTAB 40//config: help 41//config: When respawn entries are removed from inittab and a SIGHUP is 42//config: sent to init, this option will make init kill the processes 43//config: that have been removed. 44//config: 45//config:config FEATURE_KILL_DELAY 46//config: int "How long to wait between TERM and KILL (0 - send TERM only)" if FEATURE_KILL_REMOVED 47//config: range 0 1024 48//config: default 0 49//config: depends on FEATURE_KILL_REMOVED 50//config: help 51//config: With nonzero setting, init sends TERM, forks, child waits N 52//config: seconds, sends KILL and exits. Setting it too high is unwise 53//config: (child will hang around for too long and could actually kill 54//config: the wrong process!) 55//config: 56//config:config FEATURE_INIT_SCTTY 57//config: bool "Run commands with leading dash with controlling tty" 58//config: default y 59//config: depends on INIT || LINUXRC 60//config: help 61//config: If this option is enabled, init will try to give a controlling 62//config: tty to any command which has leading hyphen (often it's "-/bin/sh"). 63//config: More precisely, init will do "ioctl(STDIN_FILENO, TIOCSCTTY, 0)". 64//config: If device attached to STDIN_FILENO can be a ctty but is not yet 65//config: a ctty for other session, it will become this process' ctty. 66//config: This is not the traditional init behavour, but is often what you want 67//config: in an embedded system where the console is only accessed during 68//config: development or for maintenance. 69//config: NB: using cttyhack applet may work better. 70//config: 71//config:config FEATURE_INIT_SYSLOG 72//config: bool "Enable init to write to syslog" 73//config: default y 74//config: depends on INIT || LINUXRC 75//config: help 76//config: If selected, some init messages are sent to syslog. 77//config: Otherwise, they are sent to VT #5 if linux virtual tty is detected 78//config: (if not, no separate logging is done). 79//config: 80//config:config FEATURE_INIT_QUIET 81//config: bool "Be quiet on boot (no 'init started:' message)" 82//config: default y 83//config: depends on INIT || LINUXRC 84//config: 85//config:config FEATURE_INIT_COREDUMPS 86//config: bool "Support dumping core for child processes (debugging only)" 87//config: default n # not Y because this is a debug option 88//config: depends on INIT || LINUXRC 89//config: help 90//config: If this option is enabled and the file /.init_enable_core 91//config: exists, then init will call setrlimit() to allow unlimited 92//config: core file sizes. If this option is disabled, processes 93//config: will not generate any core files. 94//config: 95//config:config INIT_TERMINAL_TYPE 96//config: string "Initial terminal type" 97//config: default "linux" 98//config: depends on INIT || LINUXRC 99//config: help 100//config: This is the initial value set by init for the TERM environment 101//config: variable. This variable is used by programs which make use of 102//config: extended terminal capabilities. 103//config: 104//config: Note that on Linux, init attempts to detect serial terminal and 105//config: sets TERM to "vt102" if one is found. 106//config: 107//config:config FEATURE_INIT_MODIFY_CMDLINE 108//config: bool "Clear init's command line" 109//config: default y 110//config: depends on INIT || LINUXRC 111//config: help 112//config: When launched as PID 1 and after parsing its arguments, init 113//config: wipes all the arguments but argv[0] and rewrites argv[0] to 114//config: contain only "init", so that its command line appears solely as 115//config: "init" in tools such as ps. 116//config: If this option is set to Y, init will keep its original behavior, 117//config: otherwise, all the arguments including argv[0] will be preserved, 118//config: be they parsed or ignored by init. 119//config: The original command-line used to launch init can then be 120//config: retrieved in /proc/1/cmdline on Linux, for example. 121 122//applet:IF_INIT(APPLET(init, BB_DIR_SBIN, BB_SUID_DROP)) 123//applet:IF_LINUXRC(APPLET_ODDNAME(linuxrc, init, BB_DIR_ROOT, BB_SUID_DROP, linuxrc)) 124 125//kbuild:lib-$(CONFIG_INIT) += init.o 126//kbuild:lib-$(CONFIG_LINUXRC) += init.o 127 128#define DEBUG_SEGV_HANDLER 0 129 130#include "libbb.h" 131#include "common_bufsiz.h" 132#include <syslog.h> 133#ifdef __linux__ 134# include <linux/vt.h> 135# include <sys/sysinfo.h> 136#endif 137#include "reboot.h" /* reboot() constants */ 138 139#if DEBUG_SEGV_HANDLER 140# undef _GNU_SOURCE 141# define _GNU_SOURCE 1 142# undef __USE_GNU 143# define __USE_GNU 1 144# include <execinfo.h> 145# include <sys/ucontext.h> 146#endif 147 148/* Used only for sanitizing purposes in set_sane_term() below. On systems where 149 * the baud rate is stored in a separate field, we can safely disable them. */ 150#ifndef CBAUD 151# define CBAUD 0 152# define CBAUDEX 0 153#endif 154 155/* Was a CONFIG_xxx option. A lot of people were building 156 * not fully functional init by switching it on! */ 157#define DEBUG_INIT 0 158 159#define CONSOLE_NAME_SIZE 32 160 161/* Default sysinit script. */ 162#ifndef INIT_SCRIPT 163# define INIT_SCRIPT "/etc/init.d/rcS" 164#endif 165 166/* Each type of actions can appear many times. They will be 167 * handled in order. RESTART is an exception, only 1st is used. 168 */ 169/* Start these actions first and wait for completion */ 170#define SYSINIT 0x01 171/* Start these after SYSINIT and wait for completion */ 172#define WAIT 0x02 173/* Start these after WAIT and *dont* wait for completion */ 174#define ONCE 0x04 175/* 176 * NB: while SYSINIT/WAIT/ONCE are being processed, 177 * SIGHUP ("reread /etc/inittab") will be processed only after 178 * each group of actions. If new inittab adds, say, a SYSINIT action, 179 * it will not be run, since init is already "past SYSINIT stage". 180 */ 181/* Start these after ONCE are started, restart on exit */ 182#define RESPAWN 0x08 183/* Like RESPAWN, but wait for <Enter> to be pressed on tty */ 184#define ASKFIRST 0x10 185/* 186 * Start these on SIGINT, and wait for completion. 187 * Then go back to respawning RESPAWN and ASKFIRST actions. 188 * NB: kernel sends SIGINT to us if Ctrl-Alt-Del was pressed. 189 */ 190#define CTRLALTDEL 0x20 191/* 192 * Start these before killing all processes in preparation for 193 * running RESTART actions or doing low-level halt/reboot/poweroff 194 * (initiated by SIGUSR1/SIGTERM/SIGUSR2). 195 * Wait for completion before proceeding. 196 */ 197#define SHUTDOWN 0x40 198/* 199 * exec() on SIGQUIT. SHUTDOWN actions are started and waited for, 200 * then all processes are killed, then init exec's 1st RESTART action, 201 * replacing itself by it. If no RESTART action specified, 202 * SIGQUIT has no effect. 203 */ 204#define RESTART 0x80 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 215struct globals { 216 struct init_action *init_action_list; 217#if !ENABLE_FEATURE_INIT_SYSLOG 218 const char *log_console; 219#endif 220} FIX_ALIASING; 221#define G (*(struct globals*)bb_common_bufsiz1) 222#define INIT_G() do { \ 223 setup_common_bufsiz(); \ 224 IF_NOT_FEATURE_INIT_SYSLOG(G.log_console = VC_5;) \ 225} while (0) 226 227enum { 228 L_LOG = 0x1, 229 L_CONSOLE = 0x2, 230}; 231 232/* Print a message to the specified device. 233 * "where" may be bitwise-or'd from L_LOG | L_CONSOLE 234 * NB: careful, we can be called after vfork! 235 */ 236#define dbg_message(...) do { if (DEBUG_INIT) message(__VA_ARGS__); } while (0) 237static void message(int where, const char *fmt, ...) 238 __attribute__ ((format(printf, 2, 3))); 239static void message(int where, const char *fmt, ...) 240{ 241 va_list arguments; 242 unsigned l; 243 char msg[128]; 244 245 msg[0] = '\r'; 246 va_start(arguments, fmt); 247 l = 1 + vsnprintf(msg + 1, sizeof(msg) - 2, fmt, arguments); 248 if (l > sizeof(msg) - 2) 249 l = sizeof(msg) - 2; 250 va_end(arguments); 251 252#if ENABLE_FEATURE_INIT_SYSLOG 253 msg[l] = '\0'; 254 if (where & L_LOG) { 255 /* Log the message to syslogd */ 256 openlog(applet_name, 0, LOG_DAEMON); 257 /* don't print "\r" */ 258 syslog(LOG_INFO, "%s", msg + 1); 259 closelog(); 260 } 261 msg[l++] = '\n'; 262 msg[l] = '\0'; 263#else 264 msg[l++] = '\n'; 265 msg[l] = '\0'; 266 if (where & L_LOG) { 267 /* Take full control of the log tty, and never close it. 268 * It's mine, all mine! Muhahahaha! */ 269 static int log_fd = -1; 270 271 if (log_fd < 0) { 272 log_fd = STDERR_FILENO; 273 if (G.log_console) { 274 log_fd = device_open(G.log_console, O_WRONLY | O_NONBLOCK | O_NOCTTY); 275 if (log_fd < 0) { 276 bb_error_msg("can't log to %s", G.log_console); 277 where = L_CONSOLE; 278 } else { 279 close_on_exec_on(log_fd); 280 } 281 } 282 } 283 full_write(log_fd, msg, l); 284 if (log_fd == STDERR_FILENO) 285 return; /* don't print dup messages */ 286 } 287#endif 288 289 if (where & L_CONSOLE) { 290 /* Send console messages to console so people will see them. */ 291 full_write(STDERR_FILENO, msg, l); 292 } 293} 294 295static void console_init(void) 296{ 297#ifdef VT_OPENQRY 298 int vtno; 299#endif 300 char *s; 301 302 s = getenv("CONSOLE"); 303 if (!s) 304 s = getenv("console"); 305#if defined(__FreeBSD__) || defined(__FreeBSD_kernel__) 306 /* BSD people say their kernels do not open fd 0,1,2; they need this: */ 307 if (!s) 308 s = (char*)"/dev/console"; 309#endif 310 if (s) { 311 int fd = open(s, O_RDWR | O_NONBLOCK | O_NOCTTY); 312 if (fd >= 0) { 313 dup2(fd, STDIN_FILENO); 314 dup2(fd, STDOUT_FILENO); 315 xmove_fd(fd, STDERR_FILENO); 316 } 317 dbg_message(L_LOG, "console='%s'", s); 318 } else { 319 /* Make sure fd 0,1,2 are not closed 320 * (so that they won't be used by future opens) */ 321 bb_sanitize_stdio(); 322// Users report problems 323// /* Make sure init can't be blocked by writing to stderr */ 324// fcntl(STDERR_FILENO, F_SETFL, fcntl(STDERR_FILENO, F_GETFL) | O_NONBLOCK); 325 } 326 327 s = getenv("TERM"); 328#ifdef VT_OPENQRY 329 if (ioctl(STDIN_FILENO, VT_OPENQRY, &vtno) != 0) { 330 /* Not a linux terminal, probably serial console. 331 * Force the TERM setting to vt102 332 * if TERM is set to linux (the default) */ 333 if (!s || strcmp(s, "linux") == 0) 334 putenv((char*)"TERM=vt102"); 335# if !ENABLE_FEATURE_INIT_SYSLOG 336 G.log_console = NULL; 337# endif 338 } else 339#endif 340 if (!s) 341 putenv((char*)"TERM=" CONFIG_INIT_TERMINAL_TYPE); 342} 343 344/* Set terminal settings to reasonable defaults. 345 * NB: careful, we can be called after vfork! */ 346static void set_sane_term(void) 347{ 348 struct termios tty; 349 350 tcgetattr(STDIN_FILENO, &tty); 351 352 /* set control chars */ 353 tty.c_cc[VINTR] = 3; /* C-c */ 354 tty.c_cc[VQUIT] = 28; /* C-\ */ 355 tty.c_cc[VERASE] = 127; /* C-? */ 356 tty.c_cc[VKILL] = 21; /* C-u */ 357 tty.c_cc[VEOF] = 4; /* C-d */ 358 tty.c_cc[VSTART] = 17; /* C-q */ 359 tty.c_cc[VSTOP] = 19; /* C-s */ 360 tty.c_cc[VSUSP] = 26; /* C-z */ 361 362#ifdef __linux__ 363 /* use line discipline 0 */ 364 tty.c_line = 0; 365#endif 366 367 /* Make it be sane */ 368#ifndef CRTSCTS 369# define CRTSCTS 0 370#endif 371 /* added CRTSCTS to fix Debian bug 528560 */ 372 tty.c_cflag &= CBAUD | CBAUDEX | CSIZE | CSTOPB | PARENB | PARODD | CRTSCTS; 373 tty.c_cflag |= CREAD | HUPCL | CLOCAL; 374 375 /* input modes */ 376 tty.c_iflag = ICRNL | IXON | IXOFF; 377 378 /* output modes */ 379 tty.c_oflag = OPOST | ONLCR; 380 381 /* local modes */ 382 tty.c_lflag = ISIG | ICANON | ECHO | ECHOE | ECHOK | ECHOCTL | ECHOKE | IEXTEN; 383 384 tcsetattr_stdin_TCSANOW(&tty); 385} 386 387/* Open the new terminal device. 388 * NB: careful, we can be called after vfork! */ 389static int open_stdio_to_tty(const char* tty_name) 390{ 391 /* empty tty_name means "use init's tty", else... */ 392 if (tty_name[0]) { 393 int fd; 394 395 close(STDIN_FILENO); 396 /* fd can be only < 0 or 0: */ 397 fd = device_open(tty_name, O_RDWR); 398 if (fd) { 399 message(L_LOG | L_CONSOLE, "can't open %s: "STRERROR_FMT, 400 tty_name 401 STRERROR_ERRNO 402 ); 403 return 0; /* failure */ 404 } 405 dup2(STDIN_FILENO, STDOUT_FILENO); 406 dup2(STDIN_FILENO, STDERR_FILENO); 407 } 408 set_sane_term(); 409 return 1; /* success */ 410} 411 412static void reset_sighandlers_and_unblock_sigs(void) 413{ 414 bb_signals(0 415 + (1 << SIGUSR1) 416 + (1 << SIGUSR2) 417 + (1 << SIGTERM) 418 + (1 << SIGQUIT) 419 + (1 << SIGINT) 420 + (1 << SIGHUP) 421 + (1 << SIGTSTP) 422 + (1 << SIGSTOP) 423 , SIG_DFL); 424 sigprocmask_allsigs(SIG_UNBLOCK); 425} 426 427/* Wrapper around exec: 428 * Takes string. 429 * If chars like '>' detected, execs '[-]/bin/sh -c "exec ......."'. 430 * Otherwise splits words on whitespace, deals with leading dash, 431 * and uses plain exec(). 432 * NB: careful, we can be called after vfork! 433 */ 434static void init_exec(const char *command) 435{ 436 /* +8 allows to write VLA sizes below more efficiently: */ 437 unsigned command_size = strlen(command) + 8; 438 /* strlen(command) + strlen("exec ")+1: */ 439 char buf[command_size]; 440 /* strlen(command) / 2 + 4: */ 441 char *cmd[command_size / 2]; 442 int dash; 443 444 dash = (command[0] == '-' /* maybe? && command[1] == '/' */); 445 command += dash; 446 447 /* See if any special /bin/sh requiring characters are present */ 448 if (strpbrk(command, "~`!$^&*()=|\\{}[];\"'<>?") != NULL) { 449 sprintf(buf, "exec %s", command); /* excluding "-" */ 450 /* NB: LIBBB_DEFAULT_LOGIN_SHELL define has leading dash */ 451 cmd[0] = (char*)(LIBBB_DEFAULT_LOGIN_SHELL + !dash); 452 cmd[1] = (char*)"-c"; 453 cmd[2] = buf; 454 cmd[3] = NULL; 455 command = LIBBB_DEFAULT_LOGIN_SHELL + 1; 456 } else { 457 /* Convert command (char*) into cmd (char**, one word per string) */ 458 char *word, *next; 459 int i = 0; 460 next = strcpy(buf, command - dash); /* command including "-" */ 461 command = next + dash; 462 while ((word = strsep(&next, " \t")) != NULL) { 463 if (*word != '\0') { /* not two spaces/tabs together? */ 464 cmd[i] = word; 465 i++; 466 } 467 } 468 cmd[i] = NULL; 469 } 470 /* If we saw leading "-", it is interactive shell. 471 * Try harder to give it a controlling tty. 472 */ 473 if (ENABLE_FEATURE_INIT_SCTTY && dash) { 474 /* _Attempt_ to make stdin a controlling tty. */ 475 ioctl(STDIN_FILENO, TIOCSCTTY, 0 /*only try, don't steal*/); 476 } 477 /* Here command never contains the dash, cmd[0] might */ 478 BB_EXECVP(command, cmd); 479 message(L_LOG | L_CONSOLE, "can't run '%s': "STRERROR_FMT, command STRERROR_ERRNO); 480 /* returns if execvp fails */ 481} 482 483/* Used only by run_actions */ 484static pid_t run(const struct init_action *a) 485{ 486 pid_t pid; 487 488 /* Careful: don't be affected by a signal in vforked child */ 489 sigprocmask_allsigs(SIG_BLOCK); 490 if (BB_MMU && (a->action_type & ASKFIRST)) 491 pid = fork(); 492 else 493 pid = vfork(); 494 if (pid < 0) 495 message(L_LOG | L_CONSOLE, "can't fork"); 496 if (pid) { 497 sigprocmask_allsigs(SIG_UNBLOCK); 498 return pid; /* Parent or error */ 499 } 500 501 /* Child */ 502 503 /* Reset signal handlers that were set by the parent process */ 504 reset_sighandlers_and_unblock_sigs(); 505 506 /* Create a new session and make ourself the process group leader */ 507 setsid(); 508 509 /* Open the new terminal device */ 510 if (!open_stdio_to_tty(a->terminal)) 511 _exit(EXIT_FAILURE); 512 513 /* NB: on NOMMU we can't wait for input in child, so 514 * "askfirst" will work the same as "respawn". */ 515 if (BB_MMU && (a->action_type & ASKFIRST)) { 516 static const char press_enter[] ALIGN1 = 517#ifdef CUSTOMIZED_BANNER 518#include CUSTOMIZED_BANNER 519#endif 520 "\nPlease press Enter to activate this console. "; 521 char c; 522 /* 523 * Save memory by not exec-ing anything large (like a shell) 524 * before the user wants it. This is critical if swap is not 525 * enabled and the system has low memory. Generally this will 526 * be run on the second virtual console, and the first will 527 * be allowed to start a shell or whatever an init script 528 * specifies. 529 */ 530 dbg_message(L_LOG, "waiting for enter to start '%s'" 531 "(pid %d, tty '%s')\n", 532 a->command, getpid(), a->terminal); 533 full_write(STDOUT_FILENO, press_enter, sizeof(press_enter) - 1); 534 while (safe_read(STDIN_FILENO, &c, 1) == 1 && c != '\n') 535 continue; 536 } 537 538 /* 539 * When a file named /.init_enable_core exists, setrlimit is called 540 * before processes are spawned to set core file size as unlimited. 541 * This is for debugging only. Don't use this is production, unless 542 * you want core dumps lying about.... 543 */ 544 if (ENABLE_FEATURE_INIT_COREDUMPS) { 545 if (access("/.init_enable_core", F_OK) == 0) { 546 struct rlimit limit; 547 limit.rlim_cur = RLIM_INFINITY; 548 limit.rlim_max = RLIM_INFINITY; 549 setrlimit(RLIMIT_CORE, &limit); 550 } 551 } 552 553 /* Log the process name and args */ 554 message(L_LOG, "starting pid %u, tty '%s': '%s'", 555 (int)getpid(), a->terminal, a->command); 556 557 /* Now run it. The new program will take over this PID, 558 * so nothing further in init.c should be run. */ 559 init_exec(a->command); 560 /* We're still here? Some error happened. */ 561 _exit(-1); 562} 563 564static struct init_action *mark_terminated(pid_t pid) 565{ 566 struct init_action *a; 567 568 if (pid > 0) { 569 update_utmp_DEAD_PROCESS(pid); 570 for (a = G.init_action_list; a; a = a->next) { 571 if (a->pid == pid) { 572 a->pid = 0; 573 return a; 574 } 575 } 576 } 577 return NULL; 578} 579 580static void waitfor(pid_t pid) 581{ 582 /* waitfor(run(x)): protect against failed fork inside run() */ 583 if (pid <= 0) 584 return; 585 586 /* Wait for any child (prevent zombies from exiting orphaned processes) 587 * but exit the loop only when specified one has exited. */ 588 while (1) { 589 pid_t wpid = wait(NULL); 590 mark_terminated(wpid); 591 /* Unsafe. SIGTSTP handler might have wait'ed it already */ 592 /*if (wpid == pid) break;*/ 593 /* More reliable: */ 594 if (kill(pid, 0)) 595 break; 596 } 597} 598 599/* Run all commands of a particular type */ 600static void run_actions(int action_type) 601{ 602 struct init_action *a; 603 604 for (a = G.init_action_list; a; a = a->next) { 605 if (!(a->action_type & action_type)) 606 continue; 607 608 if (a->action_type & (SYSINIT | WAIT | ONCE | CTRLALTDEL | SHUTDOWN)) { 609 pid_t pid = run(a); 610 if (a->action_type & (SYSINIT | WAIT | CTRLALTDEL | SHUTDOWN)) 611 waitfor(pid); 612 } 613 if (a->action_type & (RESPAWN | ASKFIRST)) { 614 /* Only run stuff with pid == 0. If pid != 0, 615 * it is already running 616 */ 617 if (a->pid == 0) 618 a->pid = run(a); 619 } 620 } 621} 622 623static void new_init_action(uint8_t action_type, const char *command, const char *cons) 624{ 625 struct init_action *a, **nextp; 626 627 /* Scenario: 628 * old inittab: 629 * ::shutdown:umount -a -r 630 * ::shutdown:swapoff -a 631 * new inittab: 632 * ::shutdown:swapoff -a 633 * ::shutdown:umount -a -r 634 * On reload, we must ensure entries end up in correct order. 635 * To achieve that, if we find a matching entry, we move it 636 * to the end. 637 */ 638 nextp = &G.init_action_list; 639 while ((a = *nextp) != NULL) { 640 /* Don't enter action if it's already in the list. 641 * This prevents losing running RESPAWNs. 642 */ 643 if (strcmp(a->command, command) == 0 644 && strcmp(a->terminal, cons) == 0 645 ) { 646 /* Remove from list */ 647 *nextp = a->next; 648 /* Find the end of the list */ 649 while (*nextp != NULL) 650 nextp = &(*nextp)->next; 651 a->next = NULL; 652 goto append; 653 } 654 nextp = &a->next; 655 } 656 657 a = xzalloc(sizeof(*a) + strlen(command)); 658 659 /* Append to the end of the list */ 660 append: 661 *nextp = a; 662 a->action_type = action_type; 663 strcpy(a->command, command); 664 safe_strncpy(a->terminal, cons, sizeof(a->terminal)); 665 dbg_message(L_LOG | L_CONSOLE, "command='%s' action=%x tty='%s'\n", 666 a->command, a->action_type, a->terminal); 667} 668 669/* NOTE that if CONFIG_FEATURE_USE_INITTAB is NOT defined, 670 * then parse_inittab() simply adds in some default 671 * actions (i.e., runs INIT_SCRIPT and then starts a pair 672 * of "askfirst" shells). If CONFIG_FEATURE_USE_INITTAB 673 * _is_ defined, but /etc/inittab is missing, this 674 * results in the same set of default behaviors. 675 */ 676static void parse_inittab(void) 677{ 678#if ENABLE_FEATURE_USE_INITTAB 679 char *token[4]; 680 parser_t *parser = config_open2("/etc/inittab", fopen_for_read); 681 682 if (parser == NULL) 683#endif 684 { 685 /* No inittab file - set up some default behavior */ 686 /* Sysinit */ 687 new_init_action(SYSINIT, INIT_SCRIPT, ""); 688 /* Askfirst shell on tty1-4 */ 689 new_init_action(ASKFIRST, bb_default_login_shell, ""); 690//TODO: VC_1 instead of ""? "" is console -> ctty problems -> angry users 691 new_init_action(ASKFIRST, bb_default_login_shell, VC_2); 692 new_init_action(ASKFIRST, bb_default_login_shell, VC_3); 693 new_init_action(ASKFIRST, bb_default_login_shell, VC_4); 694 /* Reboot on Ctrl-Alt-Del */ 695 new_init_action(CTRLALTDEL, "reboot", ""); 696 /* Umount all filesystems on halt/reboot */ 697 new_init_action(SHUTDOWN, "umount -a -r", ""); 698 /* Swapoff on halt/reboot */ 699 new_init_action(SHUTDOWN, "swapoff -a", ""); 700 /* Restart init when a QUIT is received */ 701 new_init_action(RESTART, "init", ""); 702 return; 703 } 704 705#if ENABLE_FEATURE_USE_INITTAB 706 /* optional_tty:ignored_runlevel:action:command 707 * Delims are not to be collapsed and need exactly 4 tokens 708 */ 709 while (config_read(parser, token, 4, 0, "#:", 710 PARSE_NORMAL & ~(PARSE_TRIM | PARSE_COLLAPSE))) { 711 /* order must correspond to SYSINIT..RESTART constants */ 712 static const char actions[] ALIGN1 = 713 "sysinit\0""wait\0""once\0""respawn\0""askfirst\0" 714 "ctrlaltdel\0""shutdown\0""restart\0"; 715 int action; 716 char *tty = token[0]; 717 718 if (!token[3]) /* less than 4 tokens */ 719 goto bad_entry; 720 action = index_in_strings(actions, token[2]); 721 if (action < 0 || !token[3][0]) /* token[3]: command */ 722 goto bad_entry; 723 /* turn .*TTY -> /dev/TTY */ 724 if (tty[0]) { 725 tty = concat_path_file("/dev/", skip_dev_pfx(tty)); 726 } 727 new_init_action(1 << action, token[3], tty); 728 if (tty[0]) 729 free(tty); 730 continue; 731 bad_entry: 732 message(L_LOG | L_CONSOLE, "Bad inittab entry at line %d", 733 parser->lineno); 734 } 735 config_close(parser); 736#endif 737} 738 739static void pause_and_low_level_reboot(unsigned magic) NORETURN; 740static void pause_and_low_level_reboot(unsigned magic) 741{ 742 pid_t pid; 743 744 /* Allow time for last message to reach serial console, etc */ 745 sleep(1); 746 747 /* We have to fork here, since the kernel calls do_exit(EXIT_SUCCESS) 748 * in linux/kernel/sys.c, which can cause the machine to panic when 749 * the init process exits... */ 750 pid = vfork(); 751 if (pid == 0) { /* child */ 752 reboot(magic); 753 _exit(EXIT_SUCCESS); 754 } 755 while (1) 756 sleep(1); 757} 758 759static void run_shutdown_and_kill_processes(void) 760{ 761 /* Run everything to be run at "shutdown". This is done _prior_ 762 * to killing everything, in case people wish to use scripts to 763 * shut things down gracefully... */ 764 run_actions(SHUTDOWN); 765 766 message(L_CONSOLE | L_LOG, "The system is going down NOW!"); 767 768 /* Send signals to every process _except_ pid 1 */ 769 kill(-1, SIGTERM); 770 message(L_CONSOLE, "Sent SIG%s to all processes", "TERM"); 771 sync(); 772 sleep(1); 773 774 kill(-1, SIGKILL); 775 message(L_CONSOLE, "Sent SIG%s to all processes", "KILL"); 776 sync(); 777 /*sleep(1); - callers take care about making a pause */ 778} 779 780/* Signal handling by init: 781 * 782 * For process with PID==1, on entry kernel sets all signals to SIG_DFL 783 * and unmasks all signals. However, for process with PID==1, 784 * default action (SIG_DFL) on any signal is to ignore it, 785 * even for special signals SIGKILL and SIGCONT. 786 * Also, any signal can be caught or blocked. 787 * (but SIGSTOP is still handled specially, at least in 2.6.20) 788 * 789 * We install two kinds of handlers, "immediate" and "delayed". 790 * 791 * Immediate handlers execute at any time, even while, say, sysinit 792 * is running. 793 * 794 * Delayed handlers just set a flag variable. The variable is checked 795 * in the main loop and acted upon. 796 * 797 * halt/poweroff/reboot and restart have immediate handlers. 798 * They only traverse linked list of struct action's, never modify it, 799 * this should be safe to do even in signal handler. Also they 800 * never return. 801 * 802 * SIGSTOP and SIGTSTP have immediate handlers. They just wait 803 * for SIGCONT to happen. 804 * 805 * SIGHUP has a delayed handler, because modifying linked list 806 * of struct action's from a signal handler while it is manipulated 807 * by the program may be disastrous. 808 * 809 * Ctrl-Alt-Del has a delayed handler. Not a must, but allowing 810 * it to happen even somewhere inside "sysinit" would be a bit awkward. 811 * 812 * There is a tiny probability that SIGHUP and Ctrl-Alt-Del will collide 813 * and only one will be remembered and acted upon. 814 */ 815 816/* The SIGPWR/SIGUSR[12]/SIGTERM handler */ 817static void halt_reboot_pwoff(int sig) NORETURN; 818static void halt_reboot_pwoff(int sig) 819{ 820 const char *m; 821 unsigned rb; 822 823 /* We may call run() and it unmasks signals, 824 * including the one masked inside this signal handler. 825 * Testcase which would start multiple reboot scripts: 826 * while true; do reboot; done 827 * Preventing it: 828 */ 829 reset_sighandlers_and_unblock_sigs(); 830 831 run_shutdown_and_kill_processes(); 832 833 m = "halt"; 834 rb = RB_HALT_SYSTEM; 835 if (sig == SIGTERM) { 836 m = "reboot"; 837 rb = RB_AUTOBOOT; 838 } else if (sig == SIGUSR2) { 839 m = "poweroff"; 840 rb = RB_POWER_OFF; 841 } 842 message(L_CONSOLE, "Requesting system %s", m); 843 pause_and_low_level_reboot(rb); 844 /* not reached */ 845} 846 847/* Handler for QUIT - exec "restart" action, 848 * else (no such action defined) do nothing */ 849static void exec_restart_action(void) 850{ 851 struct init_action *a; 852 853 for (a = G.init_action_list; a; a = a->next) { 854 if (!(a->action_type & RESTART)) 855 continue; 856 857 /* Starting from here, we won't return. 858 * Thus don't need to worry about preserving errno 859 * and such. 860 */ 861 862 reset_sighandlers_and_unblock_sigs(); 863 864 run_shutdown_and_kill_processes(); 865 866#ifdef RB_ENABLE_CAD 867 /* Allow Ctrl-Alt-Del to reboot the system. 868 * This is how kernel sets it up for init, we follow suit. 869 */ 870 reboot(RB_ENABLE_CAD); /* misnomer */ 871#endif 872 873 if (open_stdio_to_tty(a->terminal)) { 874 dbg_message(L_CONSOLE, "Trying to re-exec %s", a->command); 875 /* Theoretically should be safe. 876 * But in practice, kernel bugs may leave 877 * unkillable processes, and wait() may block forever. 878 * Oh well. Hoping "new" init won't be too surprised 879 * by having children it didn't create. 880 */ 881 //while (wait(NULL) > 0) 882 // continue; 883 init_exec(a->command); 884 } 885 /* Open or exec failed */ 886 pause_and_low_level_reboot(RB_HALT_SYSTEM); 887 /* not reached */ 888 } 889} 890 891/* The SIGSTOP/SIGTSTP handler 892 * NB: inside it, all signals except SIGCONT are masked 893 * via appropriate setup in sigaction(). 894 */ 895static void stop_handler(int sig UNUSED_PARAM) 896{ 897 smallint saved_bb_got_signal; 898 int saved_errno; 899 900 saved_bb_got_signal = bb_got_signal; 901 saved_errno = errno; 902 signal(SIGCONT, record_signo); 903 904 while (1) { 905 pid_t wpid; 906 907 if (bb_got_signal == SIGCONT) 908 break; 909 /* NB: this can accidentally wait() for a process 910 * which we waitfor() elsewhere! waitfor() must have 911 * code which is resilient against this. 912 */ 913 wpid = wait_any_nohang(NULL); 914 mark_terminated(wpid); 915 sleep(1); 916 } 917 918 signal(SIGCONT, SIG_DFL); 919 errno = saved_errno; 920 bb_got_signal = saved_bb_got_signal; 921} 922 923#if ENABLE_FEATURE_USE_INITTAB 924static void reload_inittab(void) 925{ 926 struct init_action *a, **nextp; 927 928 message(L_LOG, "reloading /etc/inittab"); 929 930 /* Disable old entries */ 931 for (a = G.init_action_list; a; a = a->next) 932 a->action_type = 0; 933 934 /* Append new entries, or modify existing entries 935 * (incl. setting a->action_type) if cmd and device name 936 * match new ones. End result: only entries with 937 * a->action_type == 0 are stale. 938 */ 939 parse_inittab(); 940 941#if ENABLE_FEATURE_KILL_REMOVED 942 /* Kill stale entries */ 943 /* Be nice and send SIGTERM first */ 944 for (a = G.init_action_list; a; a = a->next) 945 if (a->action_type == 0 && a->pid != 0) 946 kill(a->pid, SIGTERM); 947 if (CONFIG_FEATURE_KILL_DELAY) { 948 /* NB: parent will wait in NOMMU case */ 949 if ((BB_MMU ? fork() : vfork()) == 0) { /* child */ 950 sleep(CONFIG_FEATURE_KILL_DELAY); 951 for (a = G.init_action_list; a; a = a->next) 952 if (a->action_type == 0 && a->pid != 0) 953 kill(a->pid, SIGKILL); 954 _exit(EXIT_SUCCESS); 955 } 956 } 957#endif 958 959 /* Remove stale entries and SYSINIT entries. 960 * We never rerun SYSINIT entries anyway, 961 * removing them too saves a few bytes 962 */ 963 nextp = &G.init_action_list; 964 while ((a = *nextp) != NULL) { 965 /* 966 * Why pid == 0 check? 967 * Process can be removed from inittab and added *later*. 968 * If we delete its entry but process still runs, 969 * duplicate is spawned when the entry is re-added. 970 */ 971 if ((a->action_type & ~SYSINIT) == 0 && a->pid == 0) { 972 *nextp = a->next; 973 free(a); 974 } else { 975 nextp = &a->next; 976 } 977 } 978 979 /* Not needed: */ 980 /* run_actions(RESPAWN | ASKFIRST); */ 981 /* - we return to main loop, which does this automagically */ 982} 983#endif 984 985static int check_delayed_sigs(void) 986{ 987 int sigs_seen = 0; 988 989 while (1) { 990 smallint sig = bb_got_signal; 991 992 if (!sig) 993 return sigs_seen; 994 bb_got_signal = 0; 995 sigs_seen = 1; 996#if ENABLE_FEATURE_USE_INITTAB 997 if (sig == SIGHUP) 998 reload_inittab(); 999#endif 1000 if (sig == SIGINT)
1001 run_actions(CTRLALTDEL); 1002 if (sig == SIGQUIT) { 1003 exec_restart_action(); 1004 /* returns only if no restart action defined */ 1005 } 1006 if ((1 << sig) & (0 1007#ifdef SIGPWR 1008 + (1 << SIGPWR) 1009#endif 1010 + (1 << SIGUSR1) 1011 + (1 << SIGUSR2) 1012 + (1 << SIGTERM) 1013 )) { 1014 halt_reboot_pwoff(sig); 1015 } 1016 } 1017} 1018 1019#if DEBUG_SEGV_HANDLER 1020static 1021void handle_sigsegv(int sig, siginfo_t *info, void *ucontext) 1022{ 1023 long ip; 1024 ucontext_t *uc; 1025 1026 uc = ucontext; 1027 ip = uc->uc_mcontext.gregs[REG_EIP]; 1028 fdprintf(2, "signal:%d address:0x%lx ip:0x%lx\n", 1029 sig, 1030 /* this is void*, but using %p would print "(null)" 1031 * even for ptrs which are not exactly 0, but, say, 0x123: 1032 */ 1033 (long)info->si_addr, 1034 ip); 1035 { 1036 /* glibc extension */ 1037 void *array[50]; 1038 int size; 1039 size = backtrace(array, 50); 1040 backtrace_symbols_fd(array, size, 2); 1041 } 1042 for (;;) sleep(9999); 1043} 1044#endif 1045 1046static void sleep_much(void) 1047{ 1048 sleep(30 * 24*60*60); 1049} 1050 1051int init_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; 1052int init_main(int argc UNUSED_PARAM, char **argv) 1053{ 1054 INIT_G(); 1055 1056 if (argv[1] && strcmp(argv[1], "-q") == 0) { 1057 return kill(1, SIGHUP); 1058 } 1059 1060#if DEBUG_SEGV_HANDLER 1061 { 1062 struct sigaction sa; 1063 memset(&sa, 0, sizeof(sa)); 1064 sa.sa_sigaction = handle_sigsegv; 1065 sa.sa_flags = SA_SIGINFO; 1066 sigaction(SIGSEGV, &sa, NULL); 1067 sigaction(SIGILL, &sa, NULL); 1068 sigaction(SIGFPE, &sa, NULL); 1069 sigaction(SIGBUS, &sa, NULL); 1070 } 1071#endif 1072 1073 if (!DEBUG_INIT) { 1074 /* Some users send poweroff signals to init VERY early. 1075 * To handle this, mask signals early, 1076 * and unmask them only after signal handlers are installed. 1077 */ 1078 sigprocmask_allsigs(SIG_BLOCK); 1079 1080 /* Expect to be invoked as init with PID=1 or be invoked as linuxrc */ 1081 if (getpid() != 1 1082 && (!ENABLE_LINUXRC || applet_name[0] != 'l') /* not linuxrc? */ 1083 ) { 1084 bb_error_msg_and_die("must be run as PID 1"); 1085 } 1086#ifdef RB_DISABLE_CAD 1087 /* Turn off rebooting via CTL-ALT-DEL - we get a 1088 * SIGINT on CAD so we can shut things down gracefully... */ 1089 reboot(RB_DISABLE_CAD); /* misnomer */ 1090#endif 1091 } 1092 1093 /* If, say, xmalloc would ever die, we don't want to oops kernel 1094 * by exiting. 1095 * NB: we set die_func *after* PID 1 check and bb_show_usage. 1096 * Otherwise, for example, "init u" ("please rexec yourself" 1097 * command for sysvinit) will show help text (which isn't too bad), 1098 * *and sleep forever* (which is bad!) 1099 */ 1100 die_func = sleep_much; 1101 1102 /* Figure out where the default console should be */ 1103 console_init(); 1104 set_sane_term(); 1105 xchdir("/"); 1106 setsid(); 1107 1108 /* Make sure environs is set to something sane */ 1109 putenv((char *) "HOME=/"); 1110 putenv((char *) bb_PATH_root_path); 1111 putenv((char *) "SHELL=/bin/sh"); 1112 putenv((char *) "USER=root"); /* needed? why? */ 1113 1114 if (argv[1]) 1115 xsetenv("RUNLEVEL", argv[1]); 1116 1117#if !ENABLE_FEATURE_INIT_QUIET 1118 /* Hello world */ 1119 message(L_CONSOLE | L_LOG, "init started: %s", bb_banner); 1120#endif 1121 1122 /* Check if we are supposed to be in single user mode */ 1123 if (argv[1] 1124 && (strcmp(argv[1], "single") == 0 || strcmp(argv[1], "-s") == 0 || LONE_CHAR(argv[1], '1')) 1125 ) { 1126 /* ??? shouldn't we set RUNLEVEL="b" here? */ 1127 /* Start a shell on console */ 1128 new_init_action(RESPAWN, bb_default_login_shell, ""); 1129 } else { 1130 /* Not in single user mode - see what inittab says */ 1131 1132 /* NOTE that if CONFIG_FEATURE_USE_INITTAB is NOT defined, 1133 * then parse_inittab() simply adds in some default 1134 * actions (i.e., INIT_SCRIPT and a pair 1135 * of "askfirst" shells) */ 1136 parse_inittab(); 1137 } 1138 1139#if ENABLE_SELINUX 1140 if (getenv("SELINUX_INIT") == NULL) { 1141 int enforce = 0; 1142 1143 putenv((char*)"SELINUX_INIT=YES"); 1144 if (selinux_init_load_policy(&enforce) == 0) { 1145 BB_EXECVP(argv[0], argv); 1146 } else if (enforce > 0) { 1147 /* SELinux in enforcing mode but load_policy failed */ 1148 message(L_CONSOLE, "can't load SELinux Policy. " 1149 "Machine is in enforcing mode. Halting now."); 1150 return EXIT_FAILURE; 1151 } 1152 } 1153#endif 1154 1155 if (ENABLE_FEATURE_INIT_MODIFY_CMDLINE) { 1156 /* Make the command line just say "init" - that's all, nothing else */ 1157 strncpy(argv[0], "init", strlen(argv[0])); 1158 /* Wipe argv[1]-argv[N] so they don't clutter the ps listing */ 1159 while (*++argv) 1160 nuke_str(*argv); 1161 } 1162 1163 /* Set up signal handlers */ 1164 if (!DEBUG_INIT) { 1165 struct sigaction sa; 1166 1167 /* Stop handler must allow only SIGCONT inside itself */ 1168 memset(&sa, 0, sizeof(sa)); 1169 sigfillset(&sa.sa_mask); 1170 sigdelset(&sa.sa_mask, SIGCONT); 1171 sa.sa_handler = stop_handler; 1172 /* NB: sa_flags doesn't have SA_RESTART. 1173 * It must be able to interrupt wait(). 1174 */ 1175 sigaction_set(SIGTSTP, &sa); /* pause */ 1176 /* Does not work as intended, at least in 2.6.20. 1177 * SIGSTOP is simply ignored by init: 1178 */ 1179 sigaction_set(SIGSTOP, &sa); /* pause */ 1180 1181 /* These signals must interrupt wait(), 1182 * setting handler without SA_RESTART flag. 1183 */ 1184 bb_signals_recursive_norestart(0 1185 + (1 << SIGINT) /* Ctrl-Alt-Del */ 1186 + (1 << SIGQUIT) /* re-exec another init */ 1187#ifdef SIGPWR 1188 + (1 << SIGPWR) /* halt */ 1189#endif 1190 + (1 << SIGUSR1) /* halt */ 1191 + (1 << SIGTERM) /* reboot */ 1192 + (1 << SIGUSR2) /* poweroff */ 1193#if ENABLE_FEATURE_USE_INITTAB 1194 + (1 << SIGHUP) /* reread /etc/inittab */ 1195#endif 1196 , record_signo); 1197 1198 sigprocmask_allsigs(SIG_UNBLOCK); 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" 1392