xref: /src/sbin/init/init.c

/*	$NetBSD: init.c,v 1.58 2003/07/01 16:44:48 christos Exp $	*/

/*-
 * Copyright (c) 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Donn Seeley at Berkeley Software Design, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#ifndef lint
__COPYRIGHT("@(#) Copyright (c) 1991, 1993\n"
"	The Regents of the University of California.  All rights reserved.\n");
#endif /* not lint */

#ifndef lint
#if 0
static char sccsid[] = "@(#)init.c	8.2 (Berkeley) 4/28/95";
#else
__RCSID("$NetBSD: init.c,v 1.58 2003/07/01 16:44:48 christos Exp $");
#endif
#endif /* not lint */

#include <sys/param.h>
#include <sys/sysctl.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/mount.h>
#include <sys/sysctl.h>
#include <machine/cpu.h>

#include <db.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <time.h>
#include <ttyent.h>
#include <unistd.h>
#include <util.h>
#include <paths.h>
#include <err.h>

#include <stdarg.h>

#ifdef SECURE
#include <pwd.h>
#endif

#include "pathnames.h"

/*
 * Sleep times; used to prevent thrashing.
 */
#define	GETTY_SPACING		 5	/* N secs minimum getty spacing */
#define	GETTY_SLEEP		30	/* sleep N secs after spacing problem */
#define	WINDOW_WAIT		 3	/* wait N secs after starting window */
#define	STALL_TIMEOUT		30	/* wait N secs after warning */
#define	DEATH_WATCH		10	/* wait N secs for procs to die */


#if defined(RESCUEDIR)
#define	INIT_BSHELL	RESCUEDIR "/sh"
#define	INIT_MOUNT_MFS	RESCUEDIR "/mount_mfs"
#define	INIT_PATH	RESCUEDIR ":" _PATH_STDPATH
#else
#define	INIT_BSHELL	_PATH_BSHELL
#define	INIT_MOUNT_MFS	"/sbin/mount_mfs"
#define	INIT_PATH	_PATH_STDPATH
#endif

int main(int, char *[]);

void handle(sig_t, ...);
void delset(sigset_t *, ...);

void stall(const char *, ...)
    __attribute__((__format__(__printf__,1,2)));
void warning(const char *, ...)
    __attribute__((__format__(__printf__,1,2)));
void emergency(const char *, ...)
    __attribute__((__format__(__printf__,1,2)));
void disaster(int);
void badsys(int);

/*
 * We really need a recursive typedef...
 * The following at least guarantees that the return type of (*state_t)()
 * is sufficiently wide to hold a function pointer.
 */
typedef long (*state_func_t)(void);
typedef state_func_t (*state_t)(void);

state_func_t single_user(void);
state_func_t runcom(void);
state_func_t read_ttys(void);
state_func_t multi_user(void);
state_func_t clean_ttys(void);
state_func_t catatonia(void);
state_func_t death(void);

enum { AUTOBOOT, FASTBOOT } runcom_mode = AUTOBOOT;

void transition(state_t);
#ifndef LETS_GET_SMALL
state_t requested_transition = runcom;
#else /* LETS_GET_SMALL */
state_t requested_transition = single_user;
#endif /* LETS_GET_SMALL */

void setctty(const char *);

typedef struct init_session {
	int	se_index;		/* index of entry in ttys file */
	pid_t	se_process;		/* controlling process */
	time_t	se_started;		/* used to avoid thrashing */
	int	se_flags;		/* status of session */
#define	SE_SHUTDOWN	0x1		/* session won't be restarted */
#define	SE_PRESENT	0x2		/* session is in /etc/ttys */
	char	*se_device;		/* filename of port */
	char	*se_getty;		/* what to run on that port */
	char	**se_getty_argv;	/* pre-parsed argument array */
	char	*se_window;		/* window system (started only once) */
	char	**se_window_argv;	/* pre-parsed argument array */
	struct	init_session *se_prev;
	struct	init_session *se_next;
} session_t;

void free_session(session_t *);
session_t *new_session(session_t *, int, struct ttyent *);
session_t *sessions;

char **construct_argv(char *);
void start_window_system(session_t *);
void collect_child(pid_t, int);
pid_t start_getty(session_t *);
void transition_handler(int);
void alrm_handler(int);
void setsecuritylevel(int);
int getsecuritylevel(void);
int setupargv(session_t *, struct ttyent *);
int clang;

void clear_session_logs(session_t *, int);

int start_session_db(void);
void add_session(session_t *);
void del_session(session_t *);
session_t *find_session(pid_t);
DB *session_db;

#ifdef MFS_DEV_IF_NO_CONSOLE

struct mappedfile {
	const char *path;
	void	*buf;
	size_t	len;
} mfile[] = {
	{ "/dev/MAKEDEV",	NULL,	0 },
	{ "/dev/MAKEDEV.local",	NULL,	0 }
};

static int mfs_dev(void);
static void mapfile(struct mappedfile *);
static void writefile(struct mappedfile *);

#endif

/*
 * The mother of all processes.
 */
int
main(int argc, char **argv)
{
	struct sigaction sa;
	sigset_t mask;
#ifndef LETS_GET_SMALL
	int c;

	/* Dispose of random users. */
	if (getuid() != 0) {
		errno = EPERM;
		err(1, NULL);
	}

	/* System V users like to reexec init. */
	if (getpid() != 1)
		errx(1, "already running");
#endif

	/*
	 * Create an initial session.
	 */
	if (setsid() < 0)
		warn("initial setsid() failed");

	/*
	 * Establish an initial user so that programs running
	 * single user do not freak out and die (like passwd).
	 */
	if (setlogin("root") < 0)
		warn("setlogin() failed");


#ifdef MFS_DEV_IF_NO_CONSOLE
	if (mfs_dev() == -1)
		requested_transition = single_user;
#endif

#ifndef LETS_GET_SMALL
	/*
	 * Note that this does NOT open a file...
	 * Does 'init' deserve its own facility number?
	 */
	openlog("init", LOG_CONS, LOG_AUTH);
#endif /* LETS_GET_SMALL */


#ifndef LETS_GET_SMALL
	/*
	 * This code assumes that we always get arguments through flags,
	 * never through bits set in some random machine register.
	 */
	while ((c = getopt(argc, argv, "sf")) != -1)
		switch (c) {
		case 's':
			requested_transition = single_user;
			break;
		case 'f':
			runcom_mode = FASTBOOT;
			break;
		default:
			warning("unrecognized flag '-%c'", c);
			break;
		}

	if (optind != argc)
		warning("ignoring excess arguments");
#else /* LETS_GET_SMALL */
	requested_transition = single_user;
#endif /* LETS_GET_SMALL */

	/*
	 * We catch or block signals rather than ignore them,
	 * so that they get reset on exec.
	 */
	handle(badsys, SIGSYS, 0);
	handle(disaster, SIGABRT, SIGFPE, SIGILL, SIGSEGV,
	       SIGBUS, SIGXCPU, SIGXFSZ, 0);
	handle(transition_handler, SIGHUP, SIGTERM, SIGTSTP, 0);
	handle(alrm_handler, SIGALRM, 0);
	(void)sigfillset(&mask);
	delset(&mask, SIGABRT, SIGFPE, SIGILL, SIGSEGV, SIGBUS, SIGSYS,
	    SIGXCPU, SIGXFSZ, SIGHUP, SIGTERM, SIGTSTP, SIGALRM, 0);
	(void)sigprocmask(SIG_SETMASK, &mask, NULL);
	(void)sigemptyset(&sa.sa_mask);
	sa.sa_flags = 0;
	sa.sa_handler = SIG_IGN;
	(void)sigaction(SIGTTIN, &sa, NULL);
	(void)sigaction(SIGTTOU, &sa, NULL);

	/*
	 * Paranoia.
	 */
	(void)close(0);
	(void)close(1);
	(void)close(2);

	/*
	 * Start the state machine.
	 */
	transition(requested_transition);

	/*
	 * Should never reach here.
	 */
	return 1;
}

/*
 * Associate a function with a signal handler.
 */
void
handle(sig_t handler, ...)
{
	int sig;
	struct sigaction sa;
	sigset_t mask_everything;
	va_list ap;

	va_start(ap, handler);

	sa.sa_handler = handler;
	(void)sigfillset(&mask_everything);

	while ((sig = va_arg(ap, int)) != 0) {
		sa.sa_mask = mask_everything;
		/* XXX SA_RESTART? */
		sa.sa_flags = sig == SIGCHLD ? SA_NOCLDSTOP : 0;
		(void)sigaction(sig, &sa, NULL);
	}
	va_end(ap);
}

/*
 * Delete a set of signals from a mask.
 */
void
delset(sigset_t *maskp, ...)
{
	int sig;
	va_list ap;

	va_start(ap, maskp);

	while ((sig = va_arg(ap, int)) != 0)
		(void)sigdelset(maskp, sig);
	va_end(ap);
}

/*
 * Log a message and sleep for a while (to give someone an opportunity
 * to read it and to save log or hardcopy output if the problem is chronic).
 * NB: should send a message to the session logger to avoid blocking.
 */
void
stall(const char *message, ...)
{
	va_list ap;

	va_start(ap, message);
	vsyslog(LOG_ALERT, message, ap);
	va_end(ap);
	closelog();
	(void)sleep(STALL_TIMEOUT);
}

/*
 * Like stall(), but doesn't sleep.
 * If cpp had variadic macros, the two functions could be #defines for another.
 * NB: should send a message to the session logger to avoid blocking.
 */
void
warning(const char *message, ...)
{
	va_list ap;

	va_start(ap, message);
	vsyslog(LOG_ALERT, message, ap);
	va_end(ap);
	closelog();
}

/*
 * Log an emergency message.
 * NB: should send a message to the session logger to avoid blocking.
 */
void
emergency(const char *message, ...)
{
	va_list ap;

	va_start(ap, message);
	vsyslog(LOG_EMERG, message, ap);
	va_end(ap);
	closelog();
}

/*
 * Catch a SIGSYS signal.
 *
 * These may arise if a system does not support sysctl.
 * We tolerate up to 25 of these, then throw in the towel.
 */
void
badsys(int sig)
{
	static int badcount = 0;

	if (badcount++ < 25)
		return;
	disaster(sig);
}

/*
 * Catch an unexpected signal.
 */
void
disaster(int sig)
{

	emergency("fatal signal: %s", strsignal(sig));
	(void)sleep(STALL_TIMEOUT);
	_exit(sig);		/* reboot */
}

/*
 * Get the security level of the kernel.
 */
int
getsecuritylevel(void)
{
#ifdef KERN_SECURELVL
	int name[2], curlevel;
	size_t len;

	name[0] = CTL_KERN;
	name[1] = KERN_SECURELVL;
	len = sizeof curlevel;
	if (sysctl(name, 2, &curlevel, &len, NULL, 0) == -1) {
		emergency("cannot get kernel security level: %m");
		return (-1);
	}
	return (curlevel);
#else
	return (-1);
#endif
}

/*
 * Set the security level of the kernel.
 */
void
setsecuritylevel(int newlevel)
{
#ifdef KERN_SECURELVL
	int name[2], curlevel;

	curlevel = getsecuritylevel();
	if (newlevel == curlevel)
		return;
	name[0] = CTL_KERN;
	name[1] = KERN_SECURELVL;
	if (sysctl(name, 2, NULL, NULL, &newlevel, sizeof newlevel) == -1) {
		emergency( "cannot change kernel security level from"
		    " %d to %d: %m", curlevel, newlevel);
		return;
	}
#ifdef SECURE
	warning("kernel security level changed from %d to %d",
	    curlevel, newlevel);
#endif
#endif
}

/*
 * Change states in the finite state machine.
 * The initial state is passed as an argument.
 */
void
transition(state_t s)
{

	if (s == NULL)
		return;
	for (;;)
		s = (state_t)(*s)();
}

/*
 * Close out the accounting files for a login session.
 * NB: should send a message to the session logger to avoid blocking.
 */
void
clear_session_logs(session_t *sp, int status)
{
	char *line = sp->se_device + sizeof(_PATH_DEV) - 1;

#ifdef SUPPORT_UTMPX
	if (logoutx(line, status, DEAD_PROCESS))
		logwtmpx(line, "", "", status, DEAD_PROCESS);
#endif
#ifdef SUPPORT_UTMP
	if (logout(line))
		logwtmp(line, "", "");
#endif
}

/*
 * Start a session and allocate a controlling terminal.
 * Only called by children of init after forking.
 */
void
setctty(const char *name)
{
	int fd;

	(void) revoke(name);
	sleep(2);			/* leave DTR low */
	if ((fd = open(name, O_RDWR)) == -1) {
		stall("can't open %s: %m", name);
		_exit(1);
	}
	if (login_tty(fd) == -1) {
		stall("can't get %s for controlling terminal: %m", name);
		_exit(1);
	}
}

/*
 * Bring the system up single user.
 */
state_func_t
single_user(void)
{
	pid_t pid, wpid;
	int status;
	int from_securitylevel;
	sigset_t mask;
	struct sigaction sa, satstp, sahup;
#ifdef ALTSHELL
	const char *shell = INIT_BSHELL;
#endif
	char *argv[2];
#ifdef SECURE
	struct ttyent *typ;
	struct passwd *pp;
	char *clear, *password;
#endif
#ifdef ALTSHELL
	char altshell[128];
#endif /* ALTSHELL */

	/*
	 * If the kernel is in secure mode, downgrade it to insecure mode.
	 */
	from_securitylevel = getsecuritylevel();
	if (from_securitylevel > 0)
		setsecuritylevel(0);

	(void)sigemptyset(&sa.sa_mask);
	sa.sa_flags = 0;
	sa.sa_handler = SIG_IGN;
	(void)sigaction(SIGTSTP, &sa, &satstp);
	(void)sigaction(SIGHUP, &sa, &sahup);
	if ((pid = fork()) == 0) {
		/*
		 * Start the single user session.
		 */
		setctty(_PATH_CONSOLE);

#ifdef SECURE
		/*
		 * Check the root password.
		 * We don't care if the console is 'on' by default;
		 * it's the only tty that can be 'off' and 'secure'.
		 */
		typ = getttynam("console");
		pp = getpwnam("root");
		if (typ && (from_securitylevel >=2 || (typ->ty_status
		    & TTY_SECURE) == 0) && pp && *pp->pw_passwd != '\0') {
			(void)fprintf(stderr,
			    "Enter root password, or ^D to go multi-user\n");
			for (;;) {
				clear = getpass("Password:");
				if (clear == 0 || *clear == '\0')
					_exit(0);
				password = crypt(clear, pp->pw_passwd);
				(void)memset(clear, 0, _PASSWORD_LEN);
				if (strcmp(password, pp->pw_passwd) == 0)
					break;
				warning("single-user login failed\n");
			}
		}
		endttyent();
		endpwent();
#endif /* SECURE */

#ifdef ALTSHELL
		(void)fprintf(stderr,
		    "Enter pathname of shell or RETURN for %s: ", shell);
		if (fgets(altshell, sizeof(altshell), stdin) == NULL) {
			altshell[0] = '\0';
		} else {
			/* nuke \n */
			char *p;

			if ((p = strchr(altshell, '\n')) != NULL)
				*p = '\0';
		}

		if (altshell[0])
			shell = altshell;
#endif /* ALTSHELL */

		/*
		 * Unblock signals.
		 * We catch all the interesting ones,
		 * and those are reset to SIG_DFL on exec.
		 */
		(void)sigemptyset(&mask);
		(void)sigprocmask(SIG_SETMASK, &mask, NULL);

		/*
		 * Fire off a shell.
		 * If the default one doesn't work, try the Bourne shell.
		 */
		argv[0] = "-sh";
		argv[1] = 0;
		setenv("PATH", INIT_PATH, 1);
#ifdef ALTSHELL
		if (altshell[0])
			argv[0] = altshell;
		(void)execv(shell, argv);
		emergency("can't exec %s for single user: %m", shell);
		argv[0] = "-sh";
#endif /* ALTSHELL */
		(void)execv(INIT_BSHELL, argv);
		emergency("can't exec %s for single user: %m", INIT_BSHELL);
		(void)sleep(STALL_TIMEOUT);
		_exit(1);
	}

	if (pid == -1) {
		/*
		 * We are seriously hosed.  Do our best.
		 */
		emergency("can't fork single-user shell, trying again");
		while (waitpid(-1, NULL, WNOHANG) > 0)
			continue;
		(void)sigaction(SIGTSTP, &satstp, NULL);
		(void)sigaction(SIGHUP, &sahup, NULL);
		return (state_func_t) single_user;
	}

	requested_transition = 0;
	do {
		if ((wpid = waitpid(-1, &status, WUNTRACED)) != -1)
			collect_child(wpid, status);
		if (wpid == -1) {
			if (errno == EINTR)
				continue;
			warning("wait for single-user shell failed: %m; "
			    "restarting");
			return (state_func_t)single_user;
		}
		if (wpid == pid && WIFSTOPPED(status)) {
			warning("init: shell stopped, restarting\n");
			kill(pid, SIGCONT);
			wpid = -1;
		}
	} while (wpid != pid && !requested_transition);

	if (requested_transition) {
		(void)sigaction(SIGTSTP, &satstp, NULL);
		(void)sigaction(SIGHUP, &sahup, NULL);
		return (state_func_t)requested_transition;
	}

	if (WIFSIGNALED(status)) {
		if (WTERMSIG(status) == SIGKILL) {
			/* executed /sbin/reboot; wait for the end quietly */
			sigset_t s;

			(void)sigfillset(&s);
			for (;;)
				(void)sigsuspend(&s);
		} else {
			warning("single user shell terminated, restarting");
			(void)sigaction(SIGTSTP, &satstp, NULL);
			(void)sigaction(SIGHUP, &sahup, NULL);
			return (state_func_t) single_user;
		}
	}

	runcom_mode = FASTBOOT;
	(void)sigaction(SIGTSTP, &satstp, NULL);
	(void)sigaction(SIGHUP, &sahup, NULL);
#ifndef LETS_GET_SMALL
	return (state_func_t) runcom;
#else /* LETS_GET_SMALL */
	return (state_func_t) single_user;
#endif /* LETS_GET_SMALL */
}

#ifndef LETS_GET_SMALL
/*
 * Run the system startup script.
 */
state_func_t
runcom(void)
{
	pid_t pid, wpid;
	int status;
	char *argv[4];
	struct sigaction sa;

	switch ((pid = fork())) {
	case 0:
		(void)sigemptyset(&sa.sa_mask);
		sa.sa_flags = 0;
		sa.sa_handler = SIG_IGN;
		(void)sigaction(SIGTSTP, &sa, NULL);
		(void)sigaction(SIGHUP, &sa, NULL);

		setctty(_PATH_CONSOLE);

		argv[0] = "sh";
		argv[1] = _PATH_RUNCOM;
		argv[2] = runcom_mode == AUTOBOOT ? "autoboot" : 0;
		argv[3] = 0;

		(void)sigprocmask(SIG_SETMASK, &sa.sa_mask, NULL);

		(void)execv(INIT_BSHELL, argv);
		stall("can't exec %s for %s: %m", INIT_BSHELL, _PATH_RUNCOM);
		_exit(1);	/* force single user mode */
		/*NOTREACHED*/
	case -1:
		emergency("can't fork for %s on %s: %m", INIT_BSHELL,
		    _PATH_RUNCOM);
		while (waitpid(-1, NULL, WNOHANG) > 0)
			continue;
		(void)sleep(STALL_TIMEOUT);
		return (state_func_t)single_user;
	default:
		break;
	}

	/*
	 * Copied from single_user().  This is a bit paranoid.
	 */
	do {
		if ((wpid = waitpid(-1, &status, WUNTRACED)) != -1)
			collect_child(wpid, status);
		if (wpid == -1) {
			if (errno == EINTR)
				continue;
			warning("wait for %s on %s failed: %m; going to "
			    "single user mode", INIT_BSHELL, _PATH_RUNCOM);
			return (state_func_t)single_user;
		}
		if (wpid == pid && WIFSTOPPED(status)) {
			warning("init: %s on %s stopped, restarting\n",
			    INIT_BSHELL, _PATH_RUNCOM);
			(void)kill(pid, SIGCONT);
			wpid = -1;
		}
	} while (wpid != pid);

	if (WIFSIGNALED(status) && WTERMSIG(status) == SIGTERM &&
	    requested_transition == catatonia) {
		/* /etc/rc executed /sbin/reboot; wait for the end quietly */
		sigset_t s;

		(void)sigfillset(&s);
		for (;;)
			(void)sigsuspend(&s);
	}

	if (!WIFEXITED(status)) {
		warning("%s on %s terminated abnormally, going to "
		    "single user mode", INIT_BSHELL, _PATH_RUNCOM);
		return (state_func_t)single_user;
	}

	if (WEXITSTATUS(status))
		return (state_func_t)single_user;

	runcom_mode = AUTOBOOT;		/* the default */
	/* NB: should send a message to the session logger to avoid blocking. */
#ifdef SUPPORT_UTMPX
	logwtmpx("~", "reboot", "", 0, INIT_PROCESS);
#endif
#ifdef SUPPORT_UTMP
	logwtmp("~", "reboot", "");
#endif
	return (state_func_t) read_ttys;
}

/*
 * Open the session database.
 *
 * NB: We could pass in the size here; is it necessary?
 */
int
start_session_db(void)
{

	if (session_db && (*session_db->close)(session_db))
		emergency("session database close: %m");
	if ((session_db = dbopen(NULL, O_RDWR, 0, DB_HASH, NULL)) == 0) {
		emergency("session database open: %m");
		return (1);
	}
	return (0);

}

/*
 * Add a new login session.
 */
void
add_session(session_t *sp)
{
	DBT key;
	DBT data;

	if (session_db == NULL)
		return;

	key.data = &sp->se_process;
	key.size = sizeof sp->se_process;
	data.data = &sp;
	data.size = sizeof sp;

	if ((*session_db->put)(session_db, &key, &data, 0))
		emergency("insert %d: %m", sp->se_process);
}

/*
 * Delete an old login session.
 */
void
del_session(session_t *sp)
{
	DBT key;

	key.data = &sp->se_process;
	key.size = sizeof sp->se_process;

	if ((*session_db->del)(session_db, &key, 0))
		emergency("delete %d: %m", sp->se_process);
}

/*
 * Look up a login session by pid.
 */
session_t *
find_session(pid_t pid)
{
	DBT key;
	DBT data;
	session_t *ret;

	if (session_db == NULL)
		return NULL;

	key.data = &pid;
	key.size = sizeof pid;
	if ((*session_db->get)(session_db, &key, &data, 0) != 0)
		return 0;
	(void)memmove(&ret, data.data, sizeof(ret));
	return ret;
}

/*
 * Construct an argument vector from a command line.
 */
char **
construct_argv(char *command)
{
	int argc = 0;
	char **argv = malloc(((strlen(command) + 1) / 2 + 1) * sizeof (char *));
	static const char separators[] = " \t";

	if ((argv[argc++] = strtok(command, separators)) == 0)
		return (NULL);
	while ((argv[argc++] = strtok(NULL, separators)) != NULL)
		continue;
	return (argv);
}

/*
 * Deallocate a session descriptor.
 */
void
free_session(session_t *sp)
{

	free(sp->se_device);
	if (sp->se_getty) {
		free(sp->se_getty);
		free(sp->se_getty_argv);
	}
	if (sp->se_window) {
		free(sp->se_window);
		free(sp->se_window_argv);
	}
	free(sp);
}

/*
 * Allocate a new session descriptor.
 */
session_t *
new_session(session_t *sprev, int session_index, struct ttyent *typ)
{
	session_t *sp;

	if ((typ->ty_status & TTY_ON) == 0 || typ->ty_name == NULL ||
	    typ->ty_getty == NULL)
		return (NULL);

	sp = malloc(sizeof (session_t));
	if (sp == NULL)
		return NULL;
	memset(sp, 0, sizeof *sp);

	sp->se_flags = SE_PRESENT;
	sp->se_index = session_index;

	sp->se_device = malloc(sizeof(_PATH_DEV) + strlen(typ->ty_name));
	(void)sprintf(sp->se_device, "%s%s", _PATH_DEV, typ->ty_name);

	if (setupargv(sp, typ) == 0) {
		free_session(sp);
		return (NULL);
	}

	sp->se_next = NULL;
	if (sprev == NULL) {
		sessions = sp;
		sp->se_prev = NULL;
	} else {
		sprev->se_next = sp;
		sp->se_prev = sprev;
	}

	return (sp);
}

/*
 * Calculate getty and if useful window argv vectors.
 */
int
setupargv(session_t *sp, struct ttyent *typ)
{

	if (sp->se_getty) {
		free(sp->se_getty);
		free(sp->se_getty_argv);
	}
	sp->se_getty = malloc(strlen(typ->ty_getty) + strlen(typ->ty_name) + 2);
	(void) sprintf(sp->se_getty, "%s %s", typ->ty_getty, typ->ty_name);
	sp->se_getty_argv = construct_argv(sp->se_getty);
	if (sp->se_getty_argv == NULL) {
		warning("can't parse getty for port %s", sp->se_device);
		free(sp->se_getty);
		sp->se_getty = NULL;
		return (0);
	}
	if (typ->ty_window) {
		if (sp->se_window)
			free(sp->se_window);
		sp->se_window = strdup(typ->ty_window);
		sp->se_window_argv = construct_argv(sp->se_window);
		if (sp->se_window_argv == NULL) {
			warning("can't parse window for port %s",
			    sp->se_device);
			free(sp->se_window);
			sp->se_window = NULL;
			return (0);
		}
	}
	return (1);
}

/*
 * Walk the list of ttys and create sessions for each active line.
 */
state_func_t
read_ttys(void)
{
	int session_index = 0;
	session_t *sp, *snext;
	struct ttyent *typ;

	/*
	 * Destroy any previous session state.
	 * There shouldn't be any, but just in case...
	 */
	for (sp = sessions; sp; sp = snext) {
		if (sp->se_process)
			clear_session_logs(sp, 0);
		snext = sp->se_next;
		free_session(sp);
	}
	sessions = NULL;
	if (start_session_db())
		return (state_func_t)single_user;

	/*
	 * Allocate a session entry for each active port.
	 * Note that sp starts at 0.
	 */
	while ((typ = getttyent()) != NULL)
		if ((snext = new_session(sp, ++session_index, typ)) != NULL)
			sp = snext;

	endttyent();

	return (state_func_t)multi_user;
}

/*
 * Start a window system running.
 */
void
start_window_system(session_t *sp)
{
	pid_t pid;
	sigset_t mask;

	if ((pid = fork()) == -1) {
		emergency("can't fork for window system on port %s: %m",
		    sp->se_device);
		/* hope that getty fails and we can try again */
		return;
	}

	if (pid)
		return;

	sigemptyset(&mask);
	sigprocmask(SIG_SETMASK, &mask, NULL);

	if (setsid() < 0)
		emergency("setsid failed (window) %m");

	(void)execv(sp->se_window_argv[0], sp->se_window_argv);
	stall("can't exec window system '%s' for port %s: %m",
	    sp->se_window_argv[0], sp->se_device);
	_exit(1);
}

/*
 * Start a login session running.
 */
pid_t
start_getty(session_t *sp)
{
	pid_t pid;
	sigset_t mask;
	time_t current_time = time(NULL);

	/*
	 * fork(), not vfork() -- we can't afford to block.
	 */
	if ((pid = fork()) == -1) {
		emergency("can't fork for getty on port %s: %m", sp->se_device);
		return -1;
	}

	if (pid)
		return pid;

	if (current_time > sp->se_started &&
	    current_time - sp->se_started < GETTY_SPACING) {
		warning("getty repeating too quickly on port %s, sleeping",
		    sp->se_device);
		(void)sleep(GETTY_SLEEP);
	}

	if (sp->se_window) {
		start_window_system(sp);
		(void)sleep(WINDOW_WAIT);
	}

	(void)sigemptyset(&mask);
	(void)sigprocmask(SIG_SETMASK, &mask, (sigset_t *) 0);

	(void)execv(sp->se_getty_argv[0], sp->se_getty_argv);
	stall("can't exec getty '%s' for port %s: %m",
	    sp->se_getty_argv[0], sp->se_device);
	_exit(1);
	/*NOTREACHED*/
}
#endif /* LETS_GET_SMALL */

/*
 * Collect exit status for a child.
 * If an exiting login, start a new login running.
 */
void
collect_child(pid_t pid, int status)
{
#ifndef LETS_GET_SMALL
	session_t *sp, *sprev, *snext;

	if (! sessions)
		return;

	if ((sp = find_session(pid)) == NULL)
		return;

	clear_session_logs(sp, status);
	del_session(sp);
	sp->se_process = 0;

	if (sp->se_flags & SE_SHUTDOWN) {
		if ((sprev = sp->se_prev) != NULL)
			sprev->se_next = sp->se_next;
		else
			sessions = sp->se_next;
		if ((snext = sp->se_next) != NULL)
			snext->se_prev = sp->se_prev;
		free_session(sp);
		return;
	}

	if ((pid = start_getty(sp)) == -1) {
		/* serious trouble */
		requested_transition = clean_ttys;
		return;
	}

	sp->se_process = pid;
	sp->se_started = time(NULL);
	add_session(sp);
#endif /* LETS_GET_SMALL */
}

/*
 * Catch a signal and request a state transition.
 */
void
transition_handler(int sig)
{

	switch (sig) {
#ifndef LETS_GET_SMALL
	case SIGHUP:
		requested_transition = clean_ttys;
		break;
	case SIGTERM:
		requested_transition = death;
		break;
	case SIGTSTP:
		requested_transition = catatonia;
		break;
#endif /* LETS_GET_SMALL */
	default:
		requested_transition = 0;
		break;
	}
}

#ifndef LETS_GET_SMALL
/*
 * Take the system multiuser.
 */
state_func_t
multi_user(void)
{
	pid_t pid;
	int status;
	session_t *sp;

	requested_transition = 0;

	/*
	 * If the administrator has not set the security level to -1
	 * to indicate that the kernel should not run multiuser in secure
	 * mode, and the run script has not set a higher level of security
	 * than level 1, then put the kernel into secure mode.
	 */
	if (getsecuritylevel() == 0)
		setsecuritylevel(1);

	for (sp = sessions; sp; sp = sp->se_next) {
		if (sp->se_process)
			continue;
		if ((pid = start_getty(sp)) == -1) {
			/* serious trouble */
			requested_transition = clean_ttys;
			break;
		}
		sp->se_process = pid;
		sp->se_started = time(NULL);
		add_session(sp);
	}

	while (!requested_transition)
		if ((pid = waitpid(-1, &status, 0)) != -1)
			collect_child(pid, status);

	return (state_func_t)requested_transition;
}

/*
 * This is an n-squared algorithm.  We hope it isn't run often...
 */
state_func_t
clean_ttys(void)
{
	session_t *sp, *sprev;
	struct ttyent *typ;
	int session_index = 0;
	int devlen;

	for (sp = sessions; sp; sp = sp->se_next)
		sp->se_flags &= ~SE_PRESENT;

	devlen = sizeof(_PATH_DEV) - 1;
	while ((typ = getttyent()) != NULL) {
		++session_index;

		for (sprev = 0, sp = sessions; sp; sprev = sp, sp = sp->se_next)
			if (strcmp(typ->ty_name, sp->se_device + devlen) == 0)
				break;

		if (sp) {
			sp->se_flags |= SE_PRESENT;
			if (sp->se_index != session_index) {
				warning("port %s changed utmp index from "
				    "%d to %d", sp->se_device, sp->se_index,
				    session_index);
				sp->se_index = session_index;
			}
			if ((typ->ty_status & TTY_ON) == 0 ||
			    typ->ty_getty == 0) {
				sp->se_flags |= SE_SHUTDOWN;
				if (sp->se_process != 0)
					(void)kill(sp->se_process, SIGHUP);
				continue;
			}
			sp->se_flags &= ~SE_SHUTDOWN;
			if (setupargv(sp, typ) == 0) {
				warning("can't parse getty for port %s",
				    sp->se_device);
				sp->se_flags |= SE_SHUTDOWN;
				if (sp->se_process != 0)
					(void)kill(sp->se_process, SIGHUP);
			}
			continue;
		}

		new_session(sprev, session_index, typ);
	}

	endttyent();

	for (sp = sessions; sp; sp = sp->se_next)
		if ((sp->se_flags & SE_PRESENT) == 0) {
			sp->se_flags |= SE_SHUTDOWN;
			if (sp->se_process != 0)
				(void)kill(sp->se_process, SIGHUP);
		}

	return (state_func_t)multi_user;
}

/*
 * Block further logins.
 */
state_func_t
catatonia(void)
{
	session_t *sp;

	for (sp = sessions; sp; sp = sp->se_next)
		sp->se_flags |= SE_SHUTDOWN;

	return (state_func_t)multi_user;
}
#endif /* LETS_GET_SMALL */

/*
 * Note SIGALRM.
 */
void
/*ARGSUSED*/
alrm_handler(int sig)
{

	clang = 1;
}

#ifndef LETS_GET_SMALL
/*
 * Bring the system down to single user.
 */
state_func_t
death(void)
{
	session_t *sp;
	int i, status;
	pid_t pid;
	static const int death_sigs[3] = { SIGHUP, SIGTERM, SIGKILL };

	for (sp = sessions; sp; sp = sp->se_next)
		sp->se_flags |= SE_SHUTDOWN;

	/* NB: should send a message to the session logger to avoid blocking. */
#ifdef SUPPORT_UTMPX
	logwtmpx("~", "shutdown", "", 0, INIT_PROCESS);
#endif
#ifdef SUPPORT_UTMP
	logwtmp("~", "shutdown", "");
#endif

	for (i = 0; i < 3; ++i) {
		if (kill(-1, death_sigs[i]) == -1 && errno == ESRCH)
			return (state_func_t)single_user;

		clang = 0;
		alarm(DEATH_WATCH);
		do
			if ((pid = waitpid(-1, &status, 0)) != -1)
				collect_child(pid, status);
		while (clang == 0 && errno != ECHILD);

		if (errno == ECHILD)
			return (state_func_t)single_user;
	}

	warning("some processes would not die; ps axl advised");

	return (state_func_t)single_user;
}
#endif /* LETS_GET_SMALL */

#ifdef MFS_DEV_IF_NO_CONSOLE

static void
mapfile(struct mappedfile *mf)
{
	int fd;
	struct stat st;

	if ((fd = open(mf->path, O_RDONLY)) != -1) {
		if (fstat(fd, &st) != -1 && (mf->buf = mmap(0,
		    (size_t)st.st_size, PROT_READ, MAP_FILE|MAP_SHARED, fd,
		    (off_t)0)) != MAP_FAILED)
			mf->len = (size_t)st.st_size;
		else
			mf->len = 0;
		(void)close(fd);
	}
}

static void
writefile(struct mappedfile *mf)
{
	int fd;

	if (mf->len && (fd = open(mf->path, O_WRONLY|O_CREAT|O_TRUNC,
	    0755)) != -1) {
		(void)write(fd, mf->buf, mf->len);
		(void)munmap(mf->buf, mf->len);
		(void)close(fd);
	}
}

static int
mfs_dev(void)
{
	/*
	 * We cannot print errors so we bail out silently...
	 */
	pid_t pid;
	int status;
	dev_t dev;
#ifdef CPU_CONSDEV
	static int name[2] = { CTL_MACHDEP, CPU_CONSDEV };
	size_t olen;
#endif

	/* If we have /dev/console, assume all is OK  */
	if (access(_PATH_CONSOLE, F_OK) != -1)
		return(0);

	/* Grab the contents of MAKEDEV */
	mapfile(&mfile[0]);

	/* Grab the contents of MAKEDEV.local */
	mapfile(&mfile[1]);

	/* Mount an mfs over /dev so we can create devices */
	switch ((pid = fork())) {
	case 0:
		(void)execl(INIT_MOUNT_MFS, "mount_mfs", "-i", "192",
		    "-s", "768", "-b", "4096", "-f", "512", "swap", "/dev",
		    NULL);
		_exit(1);
		/*NOTREACHED*/

	case -1:
		return(-1);

	default:
		if (waitpid(pid, &status, 0) == -1)
			return(-1);
		if (status != 0)
			return(-1);
		break;
	}

#ifdef CPU_CONSDEV
	olen = sizeof(dev);
	if (sysctl(name, sizeof(name) / sizeof(name[0]), &dev, &olen,
	    NULL, 0) == -1)
#endif
		dev = makedev(0, 0);

	/* Make a console for us, so we can see things happening */
	if (mknod(_PATH_CONSOLE, 0666 | S_IFCHR, dev) == -1)
		return(-1);

	(void)freopen(_PATH_CONSOLE, "a", stderr);

	warnx("Creating mfs /dev");

	/* Create a MAKEDEV script in the mfs /dev */
	writefile(&mfile[0]);

	/* Create a MAKEDEV.local script in the mfs /dev */
	writefile(&mfile[1]);

	/* Run the makedev script to create devices */
	switch ((pid = fork())) {
	case 0:
		if (chdir("/dev") == -1)
			goto fail;
		(void)execl(INIT_BSHELL, "sh", "./MAKEDEV", "init", NULL);
		goto fail;

	case -1:
		goto fail;

	default:
		if (waitpid(pid, &status, 0) == -1)
			goto fail;
		if (status != 0) {
			errno = EINVAL;
			goto fail;
		}
		break;
	}
	return(0);
fail:
	warn("Unable to run MAKEDEV");
	return(-1);
}
#endif