modified version of felker's init

Makefile

@@ -0,0 +1,19 @@
+
+SRCS = $(wildcard *.c)
+OBJS = $(SRCS:%.c=%.o)
+
+CFLAGS = -O2 -static
+LDFLAGS = -s
+
+all: init respawn
+
+clean:
+	rm -f init respawn $(OBJS)
+
+$(OBJS):
+
+%: %.o
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $<
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c -o $@ $<

init.c

@@ -0,0 +1,24 @@
+#include <signal.h>
+#include <unistd.h>
+#include <spawn.h>
+#include <sys/wait.h>
+
+int main()
+{
+	if (getpid() != 1) return 1;
+
+	sigset_t set, old;
+	sigfillset(&set);
+	sigprocmask(SIG_BLOCK, &set, &old);
+
+	posix_spawnattr_t attr;
+	posix_spawnattr_init(&attr);
+	posix_spawnattr_setsigmask(&attr, &old);
+	posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETSID|POSIX_SPAWN_SETSIGMASK);
+
+	posix_spawn(0, "/etc/rc", 0, &attr,
+		((char *[]){ "rc", 0 }),
+		((char *[]){ 0 }));
+
+	for (;;) wait(0);
+}

rc

@@ -0,0 +1,30 @@
+#!/bin/sh
+# /etc/rc — this file will be called directly by /sbin/init
+# it is safest to use absolute paths here because
+# /etc/profile is not yet loaded
+/bin/dmesg -n 1
+/bin/echo "Mounting required filesystems"
+/bin/mount -t sysfs sysfs /sys
+/bin/mount -t proc proc /proc
+/bin/echo "Mounting fstab filesystems"
+/bin/mount -a
+/bin/echo "Remounting root as read/write"
+/bin/mount / -o remount,rw
+/bin/echo "Mounting /dev/shm"
+[ -d /dev/shm ] || /bin/mkdir /dev/shm
+/bin/mount -t tmpfs tmpfs /dev/shm
+/bin/echo "Mounting /dev/pts"
+[ -d /dev/pts ] || /bin/mkdir /dev/pts
+/bin/mount -t devpts devpts /dev/pts
+/bin/echo "Mounting /tmp"
+/bin/mount -t tmpfs tmpfs /tmp
+/bin/echo "Starting mdev"
+/bin/echo /sbin/mdev > /proc/sys/kernel/hotplug
+/sbin/mdev -s
+/bin/echo "Executing init scripts"
+for FILE in /etc/rc.d/*; do
+  [ -x /etc/rc.d/$FILE ] && /etc/rc.d/$FILE start
+done
+echo "System booted with $(/bin/cat /proc/cmdline)"
+/bin/echo "Spawning TTY"
+/sbin/respawn /bin/busybox getty 38400 /dev/tty0

reboot

@@ -0,0 +1,8 @@
+#!/bin/sh
+# /sbin/reboot
+for FILE in /etc/rc.d/*; do
+  [ -x /etc/rc.d/$FILE ] && /etc/rc.d/$FILE stop
+done
+sync
+mount / -o remount,ro
+echo b >/proc/sysrq-trigger

respawn.c

@@ -0,0 +1,26 @@
+#include <signal.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <spawn.h>
+#include <sys/wait.h>
+#include <time.h>
+
+int main(int argc, char **argv)
+{
+	sigset_t set, old;
+	sigfillset(&set);
+	sigprocmask(SIG_BLOCK, &set, &old);
+
+	posix_spawnattr_t attr;
+	posix_spawnattr_init(&attr);
+	posix_spawnattr_setsigmask(&attr, &old);
+	posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETSID|POSIX_SPAWN_SETSIGMASK);
+
+	for (;;) {
+		extern char **environ;
+		pid_t pid;
+		if (posix_spawn(&pid, argv[1], 0, &attr, argv+1, environ))
+			nanosleep(&(struct timespec){.tv_nsec=100000000}, 0);
+		waitpid(pid, 0, 0);
+	}
+}

shutdown

@@ -0,0 +1,8 @@
+#!/bin/sh
+# /sbin/shutdown
+for FILE in /etc/rc.d/*; do
+  [ -x /etc/rc.d/$FILE ] && /etc/rc.d/$FILE stop
+done
+sync
+mount / -o remount,ro
+echo o >/proc/sysrq-trigger