source: MondoRescue/branches/3.2/mindi-busybox/init/init.c@ 3232

/* vi: set sw=4 ts=4: */
/*
 * Mini init implementation for busybox
 *
 * Copyright (C) 1995, 1996 by Bruce Perens <bruce@pixar.com>.
 * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
 * Adjusted by so many folks, it's impossible to keep track.
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */

//applet:IF_INIT(APPLET(init, BB_DIR_SBIN, BB_SUID_DROP))
//applet:IF_FEATURE_INITRD(APPLET_ODDNAME(linuxrc, init, BB_DIR_ROOT, BB_SUID_DROP, linuxrc))

//kbuild:lib-$(CONFIG_INIT) += init.o

//config:config INIT
//config:   bool "init"
//config:   default y
//config:   select FEATURE_SYSLOG
//config:   help
//config:     init is the first program run when the system boots.
//config:
//config:config FEATURE_USE_INITTAB
//config:   bool "Support reading an inittab file"
//config:   default y
//config:   depends on INIT
//config:   help
//config:     Allow init to read an inittab file when the system boot.
//config:
//config:config FEATURE_KILL_REMOVED
//config:   bool "Support killing processes that have been removed from inittab"
//config:   default n
//config:   depends on FEATURE_USE_INITTAB
//config:   help
//config:     When respawn entries are removed from inittab and a SIGHUP is
//config:     sent to init, this option will make init kill the processes
//config:     that have been removed.
//config:
//config:config FEATURE_KILL_DELAY
//config:   int "How long to wait between TERM and KILL (0 - send TERM only)" if FEATURE_KILL_REMOVED
//config:   range 0 1024
//config:   default 0
//config:   depends on FEATURE_KILL_REMOVED
//config:   help
//config:     With nonzero setting, init sends TERM, forks, child waits N
//config:     seconds, sends KILL and exits. Setting it too high is unwise
//config:     (child will hang around for too long and could actually kill
//config:     the wrong process!)
//config:
//config:config FEATURE_INIT_SCTTY
//config:   bool "Run commands with leading dash with controlling tty"
//config:   default y
//config:   depends on INIT
//config:   help
//config:     If this option is enabled, init will try to give a controlling
//config:     tty to any command which has leading hyphen (often it's "-/bin/sh").
//config:     More precisely, init will do "ioctl(STDIN_FILENO, TIOCSCTTY, 0)".
//config:     If device attached to STDIN_FILENO can be a ctty but is not yet
//config:     a ctty for other session, it will become this process' ctty.
//config:     This is not the traditional init behavour, but is often what you want
//config:     in an embedded system where the console is only accessed during
//config:     development or for maintenance.
//config:     NB: using cttyhack applet may work better.
//config:
//config:config FEATURE_INIT_SYSLOG
//config:   bool "Enable init to write to syslog"
//config:   default y
//config:   depends on INIT
//config:
//config:config FEATURE_EXTRA_QUIET
//config:   bool "Be _extra_ quiet on boot"
//config:   default y
//config:   depends on INIT
//config:   help
//config:     Prevent init from logging some messages to the console during boot.
//config:
//config:config FEATURE_INIT_COREDUMPS
//config:   bool "Support dumping core for child processes (debugging only)"
//config:   default y
//config:   depends on INIT
//config:   help
//config:     If this option is enabled and the file /.init_enable_core
//config:     exists, then init will call setrlimit() to allow unlimited
//config:     core file sizes. If this option is disabled, processes
//config:     will not generate any core files.
//config:
//config:config FEATURE_INITRD
//config:   bool "Support running init from within an initrd (not initramfs)"
//config:   default y
//config:   depends on INIT
//config:   help
//config:     Legacy support for running init under the old-style initrd. Allows
//config:     the name linuxrc to act as init, and it doesn't assume init is PID 1.
//config:
//config:     This does not apply to initramfs, which runs /init as PID 1 and
//config:     requires no special support.
//config:
//config:config INIT_TERMINAL_TYPE
//config:   string "Initial terminal type"
//config:   default "linux"
//config:   depends on INIT
//config:   help
//config:     This is the initial value set by init for the TERM environment
//config:     variable. This variable is used by programs which make use of
//config:     extended terminal capabilities.
//config:
//config:     Note that on Linux, init attempts to detect serial terminal and
//config:     sets TERM to "vt102" if one is found.

#define DEBUG_SEGV_HANDLER 0

#include "libbb.h"
#include <syslog.h>
#include <paths.h>
#include <sys/resource.h>
#ifdef __linux__
# include <linux/vt.h>
# include <sys/sysinfo.h>
#endif
#include "reboot.h" /* reboot() constants */

#if DEBUG_SEGV_HANDLER
# undef _GNU_SOURCE
# define _GNU_SOURCE 1
# undef __USE_GNU
# define __USE_GNU 1
# include <execinfo.h>
# include <sys/ucontext.h>
#endif

/* Used only for sanitizing purposes in set_sane_term() below. On systems where
 * the baud rate is stored in a separate field, we can safely disable them. */
#ifndef CBAUD
# define CBAUD 0
# define CBAUDEX 0
#endif

/* Was a CONFIG_xxx option. A lot of people were building
 * not fully functional init by switching it on! */
#define DEBUG_INIT 0

#define COMMAND_SIZE      256
#define CONSOLE_NAME_SIZE 32

/* Default sysinit script. */
#ifndef INIT_SCRIPT
#define INIT_SCRIPT  "/etc/init.d/rcS"
#endif

/* Each type of actions can appear many times. They will be
 * handled in order. RESTART is an exception, only 1st is used.
 */
/* Start these actions first and wait for completion */
#define SYSINIT     0x01
/* Start these after SYSINIT and wait for completion */
#define WAIT        0x02
/* Start these after WAIT and *dont* wait for completion */
#define ONCE        0x04
/*
 * NB: while SYSINIT/WAIT/ONCE are being processed,
 * SIGHUP ("reread /etc/inittab") will be processed only after
 * each group of actions. If new inittab adds, say, a SYSINIT action,
 * it will not be run, since init is already "past SYSINIT stage".
 */
/* Start these after ONCE are started, restart on exit */
#define RESPAWN     0x08
/* Like RESPAWN, but wait for <Enter> to be pressed on tty */
#define ASKFIRST    0x10
/*
 * Start these on SIGINT, and wait for completion.
 * Then go back to respawning RESPAWN and ASKFIRST actions.
 * NB: kernel sends SIGINT to us if Ctrl-Alt-Del was pressed.
 */
#define CTRLALTDEL  0x20
/*
 * Start these before killing all processes in preparation for
 * running RESTART actions or doing low-level halt/reboot/poweroff
 * (initiated by SIGUSR1/SIGTERM/SIGUSR2).
 * Wait for completion before proceeding.
 */
#define SHUTDOWN    0x40
/*
 * exec() on SIGQUIT. SHUTDOWN actions are started and waited for,
 * then all processes are killed, then init exec's 1st RESTART action,
 * replacing itself by it. If no RESTART action specified,
 * SIGQUIT has no effect.
 */
#define RESTART     0x80


/* A linked list of init_actions, to be read from inittab */
struct init_action {
    struct init_action *next;
    pid_t pid;
    uint8_t action_type;
    char terminal[CONSOLE_NAME_SIZE];
    char command[COMMAND_SIZE];
};

static struct init_action *init_action_list = NULL;

static const char *log_console = VC_5;

enum {
    L_LOG = 0x1,
    L_CONSOLE = 0x2,
};

/* Print a message to the specified device.
 * "where" may be bitwise-or'd from L_LOG | L_CONSOLE
 * NB: careful, we can be called after vfork!
 */
#define dbg_message(...) do { if (DEBUG_INIT) message(__VA_ARGS__); } while (0)
static void message(int where, const char *fmt, ...)
    __attribute__ ((format(printf, 2, 3)));
static void message(int where, const char *fmt, ...)
{
    va_list arguments;
    unsigned l;
    char msg[128];

    msg[0] = '\r';
    va_start(arguments, fmt);
    l = 1 + vsnprintf(msg + 1, sizeof(msg) - 2, fmt, arguments);
    if (l > sizeof(msg) - 1)
        l = sizeof(msg) - 1;
    va_end(arguments);

#if ENABLE_FEATURE_INIT_SYSLOG
    msg[l] = '\0';
    if (where & L_LOG) {
        /* Log the message to syslogd */
        openlog(applet_name, 0, LOG_DAEMON);
        /* don't print "\r" */
        syslog(LOG_INFO, "%s", msg + 1);
        closelog();
    }
    msg[l++] = '\n';
    msg[l] = '\0';
#else
    {
        static int log_fd = -1;

        msg[l++] = '\n';
        msg[l] = '\0';
        /* Take full control of the log tty, and never close it.
         * It's mine, all mine!  Muhahahaha! */
        if (log_fd < 0) {
            if (!log_console) {
                log_fd = STDERR_FILENO;
            } else {
                log_fd = device_open(log_console, O_WRONLY | O_NONBLOCK | O_NOCTTY);
                if (log_fd < 0) {
                    bb_error_msg("can't log to %s", log_console);
                    where = L_CONSOLE;
                } else {
                    close_on_exec_on(log_fd);
                }
            }
        }
        if (where & L_LOG) {
            full_write(log_fd, msg, l);
            if (log_fd == STDERR_FILENO)
                return; /* don't print dup messages */
        }
    }
#endif

    if (where & L_CONSOLE) {
        /* Send console messages to console so people will see them. */
        full_write(STDERR_FILENO, msg, l);
    }
}

static void console_init(void)
{
#ifdef VT_OPENQRY
    int vtno;
#endif
    char *s;

    s = getenv("CONSOLE");
    if (!s)
        s = getenv("console");
    if (s) {
        int fd = open(s, O_RDWR | O_NONBLOCK | O_NOCTTY);
        if (fd >= 0) {
            dup2(fd, STDIN_FILENO);
            dup2(fd, STDOUT_FILENO);
            xmove_fd(fd, STDERR_FILENO);
        }
        dbg_message(L_LOG, "console='%s'", s);
    } else {
        /* Make sure fd 0,1,2 are not closed
         * (so that they won't be used by future opens) */
        bb_sanitize_stdio();
// Users report problems
//      /* Make sure init can't be blocked by writing to stderr */
//      fcntl(STDERR_FILENO, F_SETFL, fcntl(STDERR_FILENO, F_GETFL) | O_NONBLOCK);
    }

    s = getenv("TERM");
#ifdef VT_OPENQRY
    if (ioctl(STDIN_FILENO, VT_OPENQRY, &vtno) != 0) {
        /* Not a linux terminal, probably serial console.
         * Force the TERM setting to vt102
         * if TERM is set to linux (the default) */
        if (!s || strcmp(s, "linux") == 0)
            putenv((char*)"TERM=vt102");
        if (!ENABLE_FEATURE_INIT_SYSLOG)
            log_console = NULL;
    } else
#endif
    if (!s)
        putenv((char*)"TERM=" CONFIG_INIT_TERMINAL_TYPE);
}

/* Set terminal settings to reasonable defaults.
 * NB: careful, we can be called after vfork! */
static void set_sane_term(void)
{
    struct termios tty;

    tcgetattr(STDIN_FILENO, &tty);

    /* set control chars */
    tty.c_cc[VINTR] = 3;    /* C-c */
    tty.c_cc[VQUIT] = 28;   /* C-\ */
    tty.c_cc[VERASE] = 127; /* C-? */
    tty.c_cc[VKILL] = 21;   /* C-u */
    tty.c_cc[VEOF] = 4; /* C-d */
    tty.c_cc[VSTART] = 17;  /* C-q */
    tty.c_cc[VSTOP] = 19;   /* C-s */
    tty.c_cc[VSUSP] = 26;   /* C-z */

#ifdef __linux__
    /* use line discipline 0 */
    tty.c_line = 0;
#endif

    /* Make it be sane */
#ifndef CRTSCTS
# define CRTSCTS 0
#endif
    /* added CRTSCTS to fix Debian bug 528560 */
    tty.c_cflag &= CBAUD | CBAUDEX | CSIZE | CSTOPB | PARENB | PARODD | CRTSCTS;
    tty.c_cflag |= CREAD | HUPCL | CLOCAL;

    /* input modes */
    tty.c_iflag = ICRNL | IXON | IXOFF;

    /* output modes */
    tty.c_oflag = OPOST | ONLCR;

    /* local modes */
    tty.c_lflag = ISIG | ICANON | ECHO | ECHOE | ECHOK | ECHOCTL | ECHOKE | IEXTEN;

    tcsetattr_stdin_TCSANOW(&tty);
}

/* Open the new terminal device.
 * NB: careful, we can be called after vfork! */
static int open_stdio_to_tty(const char* tty_name)
{
    /* empty tty_name means "use init's tty", else... */
    if (tty_name[0]) {
        int fd;

        close(STDIN_FILENO);
        /* fd can be only < 0 or 0: */
        fd = device_open(tty_name, O_RDWR);
        if (fd) {
            message(L_LOG | L_CONSOLE, "can't open %s: %s",
                tty_name, strerror(errno));
            return 0; /* failure */
        }
        dup2(STDIN_FILENO, STDOUT_FILENO);
        dup2(STDIN_FILENO, STDERR_FILENO);
    }
    set_sane_term();
    return 1; /* success */
}

static void reset_sighandlers_and_unblock_sigs(void)
{
    bb_signals(0
        + (1 << SIGUSR1)
        + (1 << SIGUSR2)
        + (1 << SIGTERM)
        + (1 << SIGQUIT)
        + (1 << SIGINT)
        + (1 << SIGHUP)
        + (1 << SIGTSTP)
        + (1 << SIGSTOP)
        , SIG_DFL);
    sigprocmask_allsigs(SIG_UNBLOCK);
}

/* Wrapper around exec:
 * Takes string (max COMMAND_SIZE chars).
 * If chars like '>' detected, execs '[-]/bin/sh -c "exec ......."'.
 * Otherwise splits words on whitespace, deals with leading dash,
 * and uses plain exec().
 * NB: careful, we can be called after vfork!
 */
static void init_exec(const char *command)
{
    char *cmd[COMMAND_SIZE / 2];
    char buf[COMMAND_SIZE + 6];  /* COMMAND_SIZE+strlen("exec ")+1 */
    int dash = (command[0] == '-' /* maybe? && command[1] == '/' */);

    command += dash;

    /* See if any special /bin/sh requiring characters are present */
    if (strpbrk(command, "~`!$^&*()=|\\{}[];\"'<>?") != NULL) {
        sprintf(buf, "exec %s", command); /* excluding "-" */
        /* NB: LIBBB_DEFAULT_LOGIN_SHELL define has leading dash */
        cmd[0] = (char*)(LIBBB_DEFAULT_LOGIN_SHELL + !dash);
        cmd[1] = (char*)"-c";
        cmd[2] = buf;
        cmd[3] = NULL;
        command = LIBBB_DEFAULT_LOGIN_SHELL + 1;
    } else {
        /* Convert command (char*) into cmd (char**, one word per string) */
        char *word, *next;
        int i = 0;
        next = strcpy(buf, command - dash); /* command including "-" */
        command = next + dash;
        while ((word = strsep(&next, " \t")) != NULL) {
            if (*word != '\0') { /* not two spaces/tabs together? */
                cmd[i] = word;
                i++;
            }
        }
        cmd[i] = NULL;
    }
    /* If we saw leading "-", it is interactive shell.
     * Try harder to give it a controlling tty.
     */
    if (ENABLE_FEATURE_INIT_SCTTY && dash) {
        /* _Attempt_ to make stdin a controlling tty. */
        ioctl(STDIN_FILENO, TIOCSCTTY, 0 /*only try, don't steal*/);
    }
    /* Here command never contains the dash, cmd[0] might */
    BB_EXECVP(command, cmd);
    message(L_LOG | L_CONSOLE, "can't run '%s': %s", command, strerror(errno));
    /* returns if execvp fails */
}

/* Used only by run_actions */
static pid_t run(const struct init_action *a)
{
    pid_t pid;

    /* Careful: don't be affected by a signal in vforked child */
    sigprocmask_allsigs(SIG_BLOCK);
    if (BB_MMU && (a->action_type & ASKFIRST))
        pid = fork();
    else
        pid = vfork();
    if (pid < 0)
        message(L_LOG | L_CONSOLE, "can't fork");
    if (pid) {
        sigprocmask_allsigs(SIG_UNBLOCK);
        return pid; /* Parent or error */
    }

    /* Child */

    /* Reset signal handlers that were set by the parent process */
    reset_sighandlers_and_unblock_sigs();

    /* Create a new session and make ourself the process group leader */
    setsid();

    /* Open the new terminal device */
    if (!open_stdio_to_tty(a->terminal))
        _exit(EXIT_FAILURE);

    /* NB: on NOMMU we can't wait for input in child, so
     * "askfirst" will work the same as "respawn". */
    if (BB_MMU && (a->action_type & ASKFIRST)) {
        static const char press_enter[] ALIGN1 =
#ifdef CUSTOMIZED_BANNER
#include CUSTOMIZED_BANNER
#endif
            "\nPlease press Enter to activate this console. ";
        char c;
        /*
         * Save memory by not exec-ing anything large (like a shell)
         * before the user wants it. This is critical if swap is not
         * enabled and the system has low memory. Generally this will
         * be run on the second virtual console, and the first will
         * be allowed to start a shell or whatever an init script
         * specifies.
         */
        dbg_message(L_LOG, "waiting for enter to start '%s'"
                    "(pid %d, tty '%s')\n",
                a->command, getpid(), a->terminal);
        full_write(STDOUT_FILENO, press_enter, sizeof(press_enter) - 1);
        while (safe_read(STDIN_FILENO, &c, 1) == 1 && c != '\n')
            continue;
    }

    /*
     * When a file named /.init_enable_core exists, setrlimit is called
     * before processes are spawned to set core file size as unlimited.
     * This is for debugging only.  Don't use this is production, unless
     * you want core dumps lying about....
     */
    if (ENABLE_FEATURE_INIT_COREDUMPS) {
        if (access("/.init_enable_core", F_OK) == 0) {
            struct rlimit limit;
            limit.rlim_cur = RLIM_INFINITY;
            limit.rlim_max = RLIM_INFINITY;
            setrlimit(RLIMIT_CORE, &limit);
        }
    }

    /* Log the process name and args */
    message(L_LOG, "starting pid %d, tty '%s': '%s'",
            getpid(), a->terminal, a->command);

    /* Now run it.  The new program will take over this PID,
     * so nothing further in init.c should be run. */
    init_exec(a->command);
    /* We're still here?  Some error happened. */
    _exit(-1);
}

static struct init_action *mark_terminated(pid_t pid)
{
    struct init_action *a;

    if (pid > 0) {
        update_utmp(pid, DEAD_PROCESS,
                /*tty_name:*/ NULL,
                /*username:*/ NULL,
                /*hostname:*/ NULL
        );
        for (a = init_action_list; a; a = a->next) {
            if (a->pid == pid) {
                a->pid = 0;
                return a;
            }
        }
    }
    return NULL;
}

static void waitfor(pid_t pid)
{
    /* waitfor(run(x)): protect against failed fork inside run() */
    if (pid <= 0)
        return;

    /* Wait for any child (prevent zombies from exiting orphaned processes)
     * but exit the loop only when specified one has exited. */
    while (1) {
        pid_t wpid = wait(NULL);
        mark_terminated(wpid);
        /* Unsafe. SIGTSTP handler might have wait'ed it already */
        /*if (wpid == pid) break;*/
        /* More reliable: */
        if (kill(pid, 0))
            break;
    }
}

/* Run all commands of a particular type */
static void run_actions(int action_type)
{
    struct init_action *a;

    for (a = init_action_list; a; a = a->next) {
        if (!(a->action_type & action_type))
            continue;

        if (a->action_type & (SYSINIT | WAIT | ONCE | CTRLALTDEL | SHUTDOWN)) {
            pid_t pid = run(a);
            if (a->action_type & (SYSINIT | WAIT | CTRLALTDEL | SHUTDOWN))
                waitfor(pid);
        }
        if (a->action_type & (RESPAWN | ASKFIRST)) {
            /* Only run stuff with pid == 0. If pid != 0,
             * it is already running
             */
            if (a->pid == 0)
                a->pid = run(a);
        }
    }
}

static void new_init_action(uint8_t action_type, const char *command, const char *cons)
{
    struct init_action *a, **nextp;

    /* Scenario:
     * old inittab:
     * ::shutdown:umount -a -r
     * ::shutdown:swapoff -a
     * new inittab:
     * ::shutdown:swapoff -a
     * ::shutdown:umount -a -r
     * On reload, we must ensure entries end up in correct order.
     * To achieve that, if we find a matching entry, we move it
     * to the end.
     */
    nextp = &init_action_list;
    while ((a = *nextp) != NULL) {
        /* Don't enter action if it's already in the list.
         * This prevents losing running RESPAWNs.
         */
        if (strcmp(a->command, command) == 0
         && strcmp(a->terminal, cons) == 0
        ) {
            /* Remove from list */
            *nextp = a->next;
            /* Find the end of the list */
            while (*nextp != NULL)
                nextp = &(*nextp)->next;
            a->next = NULL;
            goto append;
        }
        nextp = &a->next;
    }

    a = xzalloc(sizeof(*a));

    /* Append to the end of the list */
 append:
    *nextp = a;
    a->action_type = action_type;
    safe_strncpy(a->command, command, sizeof(a->command));
    safe_strncpy(a->terminal, cons, sizeof(a->terminal));
    dbg_message(L_LOG | L_CONSOLE, "command='%s' action=%d tty='%s'\n",
        a->command, a->action_type, a->terminal);
}

/* NOTE that if CONFIG_FEATURE_USE_INITTAB is NOT defined,
 * then parse_inittab() simply adds in some default
 * actions(i.e., runs INIT_SCRIPT and then starts a pair
 * of "askfirst" shells).  If CONFIG_FEATURE_USE_INITTAB
 * _is_ defined, but /etc/inittab is missing, this
 * results in the same set of default behaviors.
 */
static void parse_inittab(void)
{
#if ENABLE_FEATURE_USE_INITTAB
    char *token[4];
    parser_t *parser = config_open2("/etc/inittab", fopen_for_read);

    if (parser == NULL)
#endif
    {
        /* No inittab file - set up some default behavior */
        /* Reboot on Ctrl-Alt-Del */
        new_init_action(CTRLALTDEL, "reboot", "");
        /* Umount all filesystems on halt/reboot */
        new_init_action(SHUTDOWN, "umount -a -r", "");
        /* Swapoff on halt/reboot */
        if (ENABLE_SWAPONOFF)
            new_init_action(SHUTDOWN, "swapoff -a", "");
        /* Prepare to restart init when a QUIT is received */
        new_init_action(RESTART, "init", "");
        /* Askfirst shell on tty1-4 */
        new_init_action(ASKFIRST, bb_default_login_shell, "");
//TODO: VC_1 instead of ""? "" is console -> ctty problems -> angry users
        new_init_action(ASKFIRST, bb_default_login_shell, VC_2);
        new_init_action(ASKFIRST, bb_default_login_shell, VC_3);
        new_init_action(ASKFIRST, bb_default_login_shell, VC_4);
        /* sysinit */
        new_init_action(SYSINIT, INIT_SCRIPT, "");
        return;
    }

#if ENABLE_FEATURE_USE_INITTAB
    /* optional_tty:ignored_runlevel:action:command
     * Delims are not to be collapsed and need exactly 4 tokens
     */
    while (config_read(parser, token, 4, 0, "#:",
                PARSE_NORMAL & ~(PARSE_TRIM | PARSE_COLLAPSE))) {
        /* order must correspond to SYSINIT..RESTART constants */
        static const char actions[] ALIGN1 =
            "sysinit\0""wait\0""once\0""respawn\0""askfirst\0"
            "ctrlaltdel\0""shutdown\0""restart\0";
        int action;
        char *tty = token[0];

        if (!token[3]) /* less than 4 tokens */
            goto bad_entry;
        action = index_in_strings(actions, token[2]);
        if (action < 0 || !token[3][0]) /* token[3]: command */
            goto bad_entry;
        /* turn .*TTY -> /dev/TTY */
        if (tty[0]) {
            tty = concat_path_file("/dev/", skip_dev_pfx(tty));
        }
        new_init_action(1 << action, token[3], tty);
        if (tty[0])
            free(tty);
        continue;
 bad_entry:
        message(L_LOG | L_CONSOLE, "Bad inittab entry at line %d",
                parser->lineno);
    }
    config_close(parser);
#endif
}

static void pause_and_low_level_reboot(unsigned magic) NORETURN;
static void pause_and_low_level_reboot(unsigned magic)
{
    pid_t pid;

    /* Allow time for last message to reach serial console, etc */
    sleep(1);

    /* We have to fork here, since the kernel calls do_exit(EXIT_SUCCESS)
     * in linux/kernel/sys.c, which can cause the machine to panic when
     * the init process exits... */
    pid = vfork();
    if (pid == 0) { /* child */
        reboot(magic);
        _exit(EXIT_SUCCESS);
    }
    while (1)
        sleep(1);
}

static void run_shutdown_and_kill_processes(void)
{
    /* Run everything to be run at "shutdown".  This is done _prior_
     * to killing everything, in case people wish to use scripts to
     * shut things down gracefully... */
    run_actions(SHUTDOWN);

    message(L_CONSOLE | L_LOG, "The system is going down NOW!");

    /* Send signals to every process _except_ pid 1 */
    kill(-1, SIGTERM);
    message(L_CONSOLE | L_LOG, "Sent SIG%s to all processes", "TERM");
    sync();
    sleep(1);

    kill(-1, SIGKILL);
    message(L_CONSOLE, "Sent SIG%s to all processes", "KILL");
    sync();
    /*sleep(1); - callers take care about making a pause */
}

/* Signal handling by init:
 *
 * For process with PID==1, on entry kernel sets all signals to SIG_DFL
 * and unmasks all signals. However, for process with PID==1,
 * default action (SIG_DFL) on any signal is to ignore it,
 * even for special signals SIGKILL and SIGCONT.
 * Also, any signal can be caught or blocked.
 * (but SIGSTOP is still handled specially, at least in 2.6.20)
 *
 * We install two kinds of handlers, "immediate" and "delayed".
 *
 * Immediate handlers execute at any time, even while, say, sysinit
 * is running.
 *
 * Delayed handlers just set a flag variable. The variable is checked
 * in the main loop and acted upon.
 *
 * halt/poweroff/reboot and restart have immediate handlers.
 * They only traverse linked list of struct action's, never modify it,
 * this should be safe to do even in signal handler. Also they
 * never return.
 *
 * SIGSTOP and SIGTSTP have immediate handlers. They just wait
 * for SIGCONT to happen.
 *
 * SIGHUP has a delayed handler, because modifying linked list
 * of struct action's from a signal handler while it is manipulated
 * by the program may be disastrous.
 *
 * Ctrl-Alt-Del has a delayed handler. Not a must, but allowing
 * it to happen even somewhere inside "sysinit" would be a bit awkward.
 *
 * There is a tiny probability that SIGHUP and Ctrl-Alt-Del will collide
 * and only one will be remembered and acted upon.
 */

/* The SIGUSR[12]/SIGTERM handler */
static void halt_reboot_pwoff(int sig) NORETURN;
static void halt_reboot_pwoff(int sig)
{
    const char *m;
    unsigned rb;

    /* We may call run() and it unmasks signals,
     * including the one masked inside this signal handler.
     * Testcase which would start multiple reboot scripts:
     *  while true; do reboot; done
     * Preventing it:
     */
    reset_sighandlers_and_unblock_sigs();

    run_shutdown_and_kill_processes();

    m = "halt";
    rb = RB_HALT_SYSTEM;
    if (sig == SIGTERM) {
        m = "reboot";
        rb = RB_AUTOBOOT;
    } else if (sig == SIGUSR2) {
        m = "poweroff";
        rb = RB_POWER_OFF;
    }
    message(L_CONSOLE, "Requesting system %s", m);
    pause_and_low_level_reboot(rb);
    /* not reached */
}

/* Handler for QUIT - exec "restart" action,
 * else (no such action defined) do nothing */
static void restart_handler(int sig UNUSED_PARAM)
{
    struct init_action *a;

    for (a = init_action_list; a; a = a->next) {
        if (!(a->action_type & RESTART))
            continue;

        /* Starting from here, we won't return.
         * Thus don't need to worry about preserving errno
         * and such.
         */

        reset_sighandlers_and_unblock_sigs();

        run_shutdown_and_kill_processes();

#ifdef RB_ENABLE_CAD
        /* Allow Ctrl-Alt-Del to reboot the system.
         * This is how kernel sets it up for init, we follow suit.
         */
        reboot(RB_ENABLE_CAD); /* misnomer */
#endif

        if (open_stdio_to_tty(a->terminal)) {
            dbg_message(L_CONSOLE, "Trying to re-exec %s", a->command);
            /* Theoretically should be safe.
             * But in practice, kernel bugs may leave
             * unkillable processes, and wait() may block forever.
             * Oh well. Hoping "new" init won't be too surprised
             * by having children it didn't create.
             */
            //while (wait(NULL) > 0)
            //  continue;
            init_exec(a->command);
        }
        /* Open or exec failed */
        pause_and_low_level_reboot(RB_HALT_SYSTEM);
        /* not reached */
    }
}

/* The SIGSTOP/SIGTSTP handler
 * NB: inside it, all signals except SIGCONT are masked
 * via appropriate setup in sigaction().
 */
static void stop_handler(int sig UNUSED_PARAM)
{
    smallint saved_bb_got_signal;
    int saved_errno;

    saved_bb_got_signal = bb_got_signal;
    saved_errno = errno;
    signal(SIGCONT, record_signo);

    while (1) {
        pid_t wpid;

        if (bb_got_signal == SIGCONT)
            break;
        /* NB: this can accidentally wait() for a process
         * which we waitfor() elsewhere! waitfor() must have
         * code which is resilient against this.
         */
        wpid = wait_any_nohang(NULL);
        mark_terminated(wpid);
        sleep(1);
    }

    signal(SIGCONT, SIG_DFL);
    errno = saved_errno;
    bb_got_signal = saved_bb_got_signal;
}

#if ENABLE_FEATURE_USE_INITTAB
static void reload_inittab(void)
{
    struct init_action *a, **nextp;

    message(L_LOG, "reloading /etc/inittab");

    /* Disable old entries */
    for (a = init_action_list; a; a = a->next)
        a->action_type = 0;

    /* Append new entries, or modify existing entries
     * (incl. setting a->action_type) if cmd and device name
     * match new ones. End result: only entries with
     * a->action_type == 0 are stale.
     */
    parse_inittab();

#if ENABLE_FEATURE_KILL_REMOVED
    /* Kill stale entries */
    /* Be nice and send SIGTERM first */
    for (a = init_action_list; a; a = a->next)
        if (a->action_type == 0 && a->pid != 0)
            kill(a->pid, SIGTERM);
    if (CONFIG_FEATURE_KILL_DELAY) {
        /* NB: parent will wait in NOMMU case */
        if ((BB_MMU ? fork() : vfork()) == 0) { /* child */
            sleep(CONFIG_FEATURE_KILL_DELAY);
            for (a = init_action_list; a; a = a->next)
                if (a->action_type == 0 && a->pid != 0)
                    kill(a->pid, SIGKILL);
            _exit(EXIT_SUCCESS);
        }
    }
#endif

    /* Remove stale entries and SYSINIT entries.
     * We never rerun SYSINIT entries anyway,
     * removing them too saves a few bytes */
    nextp = &init_action_list;
    while ((a = *nextp) != NULL) {
        if ((a->action_type & ~SYSINIT) == 0) {
            *nextp = a->next;
            free(a);
        } else {
            nextp = &a->next;
        }
    }

    /* Not needed: */
    /* run_actions(RESPAWN | ASKFIRST); */
    /* - we return to main loop, which does this automagically */
}
#endif

static int check_delayed_sigs(void)
{
    int sigs_seen = 0;

    while (1) {
        smallint sig = bb_got_signal;

        if (!sig)
            return sigs_seen;
        bb_got_signal = 0;
        sigs_seen = 1;
#if ENABLE_FEATURE_USE_INITTAB
        if (sig == SIGHUP)
            reload_inittab();
#endif
        if (sig == SIGINT)
            run_actions(CTRLALTDEL);
    }
}

#if DEBUG_SEGV_HANDLER
static
void handle_sigsegv(int sig, siginfo_t *info, void *ucontext)
{
    long ip;
    ucontext_t *uc;

    uc = ucontext;
    ip = uc->uc_mcontext.gregs[REG_EIP];
    fdprintf(2, "signal:%d address:0x%lx ip:0x%lx\n",
            sig,
            /* this is void*, but using %p would print "(null)"
             * even for ptrs which are not exactly 0, but, say, 0x123:
             */
            (long)info->si_addr,
            ip);
    {
        /* glibc extension */
        void *array[50];
        int size;
        size = backtrace(array, 50);
        backtrace_symbols_fd(array, size, 2);
    }
    for (;;) sleep(9999);
}
#endif

int init_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int init_main(int argc UNUSED_PARAM, char **argv)
{
    if (argv[1] && strcmp(argv[1], "-q") == 0) {
        return kill(1, SIGHUP);
    }

#if DEBUG_SEGV_HANDLER
    {
        struct sigaction sa;
        memset(&sa, 0, sizeof(sa));
        sa.sa_sigaction = handle_sigsegv;
        sa.sa_flags = SA_SIGINFO;
        sigaction(SIGSEGV, &sa, NULL);
        sigaction(SIGILL, &sa, NULL);
        sigaction(SIGFPE, &sa, NULL);
        sigaction(SIGBUS, &sa, NULL);
    }
#endif

    if (!DEBUG_INIT) {
        /* Expect to be invoked as init with PID=1 or be invoked as linuxrc */
        if (getpid() != 1
         && (!ENABLE_FEATURE_INITRD || applet_name[0] != 'l') /* not linuxrc? */
        ) {
            bb_error_msg_and_die("must be run as PID 1");
        }
#ifdef RB_DISABLE_CAD
        /* Turn off rebooting via CTL-ALT-DEL - we get a
         * SIGINT on CAD so we can shut things down gracefully... */
        reboot(RB_DISABLE_CAD); /* misnomer */
#endif
    }

    /* If, say, xmalloc would ever die, we don't want to oops kernel
     * by exiting.
     * NB: we set die_sleep *after* PID 1 check and bb_show_usage.
     * Otherwise, for example, "init u" ("please rexec yourself"
     * command for sysvinit) will show help text (which isn't too bad),
     * *and sleep forever* (which is bad!)
     */
    die_sleep = 30 * 24*60*60;

    /* Figure out where the default console should be */
    console_init();
    set_sane_term();
    xchdir("/");
    setsid();

    /* Make sure environs is set to something sane */
    putenv((char *) "HOME=/");
    putenv((char *) bb_PATH_root_path);
    putenv((char *) "SHELL=/bin/sh");
    putenv((char *) "USER=root"); /* needed? why? */

    if (argv[1])
        xsetenv("RUNLEVEL", argv[1]);

#if !ENABLE_FEATURE_EXTRA_QUIET
    /* Hello world */
    message(L_CONSOLE | L_LOG, "init started: %s", bb_banner);
#endif

/* struct sysinfo is linux-specific */
#ifdef __linux__
    /* Make sure there is enough memory to do something useful. */
    if (ENABLE_SWAPONOFF) {
        struct sysinfo info;

        if (sysinfo(&info) == 0
         && (info.mem_unit ? info.mem_unit : 1) * (long long)info.totalram < 1024*1024
        ) {
            message(L_CONSOLE, "Low memory, forcing swapon");
            /* swapon -a requires /proc typically */
            new_init_action(SYSINIT, "mount -t proc proc /proc", "");
            /* Try to turn on swap */
            new_init_action(SYSINIT, "swapon -a", "");
            run_actions(SYSINIT);   /* wait and removing */
        }
    }
#endif

    /* Check if we are supposed to be in single user mode */
    if (argv[1]
     && (strcmp(argv[1], "single") == 0 || strcmp(argv[1], "-s") == 0 || LONE_CHAR(argv[1], '1'))
    ) {
        /* ??? shouldn't we set RUNLEVEL="b" here? */
        /* Start a shell on console */
        new_init_action(RESPAWN, bb_default_login_shell, "");
    } else {
        /* Not in single user mode - see what inittab says */

        /* NOTE that if CONFIG_FEATURE_USE_INITTAB is NOT defined,
         * then parse_inittab() simply adds in some default
         * actions(i.e., INIT_SCRIPT and a pair
         * of "askfirst" shells */
        parse_inittab();
    }

#if ENABLE_SELINUX
    if (getenv("SELINUX_INIT") == NULL) {
        int enforce = 0;

        putenv((char*)"SELINUX_INIT=YES");
        if (selinux_init_load_policy(&enforce) == 0) {
            BB_EXECVP(argv[0], argv);
        } else if (enforce > 0) {
            /* SELinux in enforcing mode but load_policy failed */
            message(L_CONSOLE, "can't load SELinux Policy. "
                "Machine is in enforcing mode. Halting now.");
            return EXIT_FAILURE;
        }
    }
#endif

    /* Make the command line just say "init"  - thats all, nothing else */
    strncpy(argv[0], "init", strlen(argv[0]));
    /* Wipe argv[1]-argv[N] so they don't clutter the ps listing */
    while (*++argv)
        memset(*argv, 0, strlen(*argv));

    /* Set up signal handlers */
    if (!DEBUG_INIT) {
        struct sigaction sa;

        bb_signals(0
            + (1 << SIGUSR1) /* halt */
            + (1 << SIGTERM) /* reboot */
            + (1 << SIGUSR2) /* poweroff */
            , halt_reboot_pwoff);
        signal(SIGQUIT, restart_handler); /* re-exec another init */

        /* Stop handler must allow only SIGCONT inside itself */
        memset(&sa, 0, sizeof(sa));
        sigfillset(&sa.sa_mask);
        sigdelset(&sa.sa_mask, SIGCONT);
        sa.sa_handler = stop_handler;
        /* NB: sa_flags doesn't have SA_RESTART.
         * It must be able to interrupt wait().
         */
        sigaction_set(SIGTSTP, &sa); /* pause */
        /* Does not work as intended, at least in 2.6.20.
         * SIGSTOP is simply ignored by init:
         */
        sigaction_set(SIGSTOP, &sa); /* pause */

        /* SIGINT (Ctrl-Alt-Del) must interrupt wait(),
         * setting handler without SA_RESTART flag.
         */
        bb_signals_recursive_norestart((1 << SIGINT), record_signo);
    }

    /* Set up "reread /etc/inittab" handler.
     * Handler is set up without SA_RESTART, it will interrupt syscalls.
     */
    if (!DEBUG_INIT && ENABLE_FEATURE_USE_INITTAB)
        bb_signals_recursive_norestart((1 << SIGHUP), record_signo);

    /* Now run everything that needs to be run */
    /* First run the sysinit command */
    run_actions(SYSINIT);
    check_delayed_sigs();
    /* Next run anything that wants to block */
    run_actions(WAIT);
    check_delayed_sigs();
    /* Next run anything to be run only once */
    run_actions(ONCE);

    /* Now run the looping stuff for the rest of forever.
     */
    while (1) {
        int maybe_WNOHANG;

        maybe_WNOHANG = check_delayed_sigs();

        /* (Re)run the respawn/askfirst stuff */
        run_actions(RESPAWN | ASKFIRST);
        maybe_WNOHANG |= check_delayed_sigs();

        /* Don't consume all CPU time - sleep a bit */
        sleep(1);
        maybe_WNOHANG |= check_delayed_sigs();

        /* Wait for any child process(es) to exit.
         *
         * If check_delayed_sigs above reported that a signal
         * was caught, wait will be nonblocking. This ensures
         * that if SIGHUP has reloaded inittab, respawn and askfirst
         * actions will not be delayed until next child death.
         */
        if (maybe_WNOHANG)
            maybe_WNOHANG = WNOHANG;
        while (1) {
            pid_t wpid;
            struct init_action *a;

            /* If signals happen _in_ the wait, they interrupt it,
             * bb_signals_recursive_norestart set them up that way
             */
            wpid = waitpid(-1, NULL, maybe_WNOHANG);
            if (wpid <= 0)
                break;

            a = mark_terminated(wpid);
            if (a) {
                message(L_LOG, "process '%s' (pid %d) exited. "
                        "Scheduling for restart.",
                        a->command, wpid);
            }
            /* See if anyone else is waiting to be reaped */
            maybe_WNOHANG = WNOHANG;
        }
    } /* while (1) */
}

//usage:#define linuxrc_trivial_usage NOUSAGE_STR
//usage:#define linuxrc_full_usage ""

//usage:#define init_trivial_usage
//usage:       ""
//usage:#define init_full_usage "\n\n"
//usage:       "Init is the parent of all processes"
//usage:
//usage:#define init_notes_usage
//usage:    "This version of init is designed to be run only by the kernel.\n"
//usage:    "\n"
//usage:    "BusyBox init doesn't support multiple runlevels. The runlevels field of\n"
//usage:    "the /etc/inittab file is completely ignored by BusyBox init. If you want\n"
//usage:    "runlevels, use sysvinit.\n"
//usage:    "\n"
//usage:    "BusyBox init works just fine without an inittab. If no inittab is found,\n"
//usage:    "it has the following default behavior:\n"
//usage:    "\n"
//usage:    "   ::sysinit:/etc/init.d/rcS\n"
//usage:    "   ::askfirst:/bin/sh\n"
//usage:    "   ::ctrlaltdel:/sbin/reboot\n"
//usage:    "   ::shutdown:/sbin/swapoff -a\n"
//usage:    "   ::shutdown:/bin/umount -a -r\n"
//usage:    "   ::restart:/sbin/init\n"
//usage:    "\n"
//usage:    "if it detects that /dev/console is _not_ a serial console, it will also run:\n"
//usage:    "\n"
//usage:    "   tty2::askfirst:/bin/sh\n"
//usage:    "   tty3::askfirst:/bin/sh\n"
//usage:    "   tty4::askfirst:/bin/sh\n"
//usage:    "\n"
//usage:    "If you choose to use an /etc/inittab file, the inittab entry format is as follows:\n"
//usage:    "\n"
//usage:    "   <id>:<runlevels>:<action>:<process>\n"
//usage:    "\n"
//usage:    "   <id>:\n"
//usage:    "\n"
//usage:    "       WARNING: This field has a non-traditional meaning for BusyBox init!\n"
//usage:    "       The id field is used by BusyBox init to specify the controlling tty for\n"
//usage:    "       the specified process to run on. The contents of this field are\n"
//usage:    "       appended to \"/dev/\" and used as-is. There is no need for this field to\n"
//usage:    "       be unique, although if it isn't you may have strange results. If this\n"
//usage:    "       field is left blank, the controlling tty is set to the console. Also\n"
//usage:    "       note that if BusyBox detects that a serial console is in use, then only\n"
//usage:    "       entries whose controlling tty is either the serial console or /dev/null\n"
//usage:    "       will be run. BusyBox init does nothing with utmp. We don't need no\n"
//usage:    "       stinkin' utmp.\n"
//usage:    "\n"
//usage:    "   <runlevels>:\n"
//usage:    "\n"
//usage:    "       The runlevels field is completely ignored.\n"
//usage:    "\n"
//usage:    "   <action>:\n"
//usage:    "\n"
//usage:    "       Valid actions include: sysinit, respawn, askfirst, wait,\n"
//usage:    "       once, restart, ctrlaltdel, and shutdown.\n"
//usage:    "\n"
//usage:    "       The available actions can be classified into two groups: actions\n"
//usage:    "       that are run only once, and actions that are re-run when the specified\n"
//usage:    "       process exits.\n"
//usage:    "\n"
//usage:    "       Run only-once actions:\n"
//usage:    "\n"
//usage:    "           'sysinit' is the first item run on boot. init waits until all\n"
//usage:    "           sysinit actions are completed before continuing. Following the\n"
//usage:    "           completion of all sysinit actions, all 'wait' actions are run.\n"
//usage:    "           'wait' actions, like 'sysinit' actions, cause init to wait until\n"
//usage:    "           the specified task completes. 'once' actions are asynchronous,\n"
//usage:    "           therefore, init does not wait for them to complete. 'restart' is\n"
//usage:    "           the action taken to restart the init process. By default this should\n"
//usage:    "           simply run /sbin/init, but can be a script which runs pivot_root or it\n"
//usage:    "           can do all sorts of other interesting things. The 'ctrlaltdel' init\n"
//usage:    "           actions are run when the system detects that someone on the system\n"
//usage:    "           console has pressed the CTRL-ALT-DEL key combination. Typically one\n"
//usage:    "           wants to run 'reboot' at this point to cause the system to reboot.\n"
//usage:    "           Finally the 'shutdown' action specifies the actions to taken when\n"
//usage:    "           init is told to reboot. Unmounting filesystems and disabling swap\n"
//usage:    "           is a very good here.\n"
//usage:    "\n"
//usage:    "       Run repeatedly actions:\n"
//usage:    "\n"
//usage:    "           'respawn' actions are run after the 'once' actions. When a process\n"
//usage:    "           started with a 'respawn' action exits, init automatically restarts\n"
//usage:    "           it. Unlike sysvinit, BusyBox init does not stop processes from\n"
//usage:    "           respawning out of control. The 'askfirst' actions acts just like\n"
//usage:    "           respawn, except that before running the specified process it\n"
//usage:    "           displays the line \"Please press Enter to activate this console.\"\n"
//usage:    "           and then waits for the user to press enter before starting the\n"
//usage:    "           specified process.\n"
//usage:    "\n"
//usage:    "       Unrecognized actions (like initdefault) will cause init to emit an\n"
//usage:    "       error message, and then go along with its business. All actions are\n"
//usage:    "       run in the order they appear in /etc/inittab.\n"
//usage:    "\n"
//usage:    "   <process>:\n"
//usage:    "\n"
//usage:    "       Specifies the process to be executed and its command line.\n"
//usage:    "\n"
//usage:    "Example /etc/inittab file:\n"
//usage:    "\n"
//usage:    "   # This is run first except when booting in single-user mode\n"
//usage:    "   #\n"
//usage:    "   ::sysinit:/etc/init.d/rcS\n"
//usage:    "   \n"
//usage:    "   # /bin/sh invocations on selected ttys\n"
//usage:    "   #\n"
//usage:    "   # Start an \"askfirst\" shell on the console (whatever that may be)\n"
//usage:    "   ::askfirst:-/bin/sh\n"
//usage:    "   # Start an \"askfirst\" shell on /dev/tty2-4\n"
//usage:    "   tty2::askfirst:-/bin/sh\n"
//usage:    "   tty3::askfirst:-/bin/sh\n"
//usage:    "   tty4::askfirst:-/bin/sh\n"
//usage:    "   \n"
//usage:    "   # /sbin/getty invocations for selected ttys\n"
//usage:    "   #\n"
//usage:    "   tty4::respawn:/sbin/getty 38400 tty4\n"
//usage:    "   tty5::respawn:/sbin/getty 38400 tty5\n"
//usage:    "   \n"
//usage:    "   \n"
//usage:    "   # Example of how to put a getty on a serial line (for a terminal)\n"
//usage:    "   #\n"
//usage:    "   #::respawn:/sbin/getty -L ttyS0 9600 vt100\n"
//usage:    "   #::respawn:/sbin/getty -L ttyS1 9600 vt100\n"
//usage:    "   #\n"
//usage:    "   # Example how to put a getty on a modem line\n"
//usage:    "   #::respawn:/sbin/getty 57600 ttyS2\n"
//usage:    "   \n"
//usage:    "   # Stuff to do when restarting the init process\n"
//usage:    "   ::restart:/sbin/init\n"
//usage:    "   \n"
//usage:    "   # Stuff to do before rebooting\n"
//usage:    "   ::ctrlaltdel:/sbin/reboot\n"
//usage:    "   ::shutdown:/bin/umount -a -r\n"
//usage:    "   ::shutdown:/sbin/swapoff -a\n"