blob: 8e4b7133be3da30557411b13b6fbb25012cd8c0c [file] [log] [blame]
/* oneit.c - tiny init replacement to launch a single child process.
* Copyright 2005, 2007 by Rob Landley <>.
USE_ONEIT(NEWTOY(oneit, "^<1nc:p3[!pn]", TOYFLAG_SBIN))
config ONEIT
bool "oneit"
default y
usage: oneit [-p] [-c /dev/tty0] command [...]
Simple init program that runs a single supplied command line with a
controlling tty (so CTRL-C can kill it).
-c Which console device to use (/dev/console doesn't do CTRL-C, etc).
-p Power off instead of rebooting when command exits.
-r Restart child when it exits.
-3 Write 32 bit PID of each exiting reparented process to fd 3 of child.
(Blocking writes, child must read to avoid eventual deadlock.)
Spawns a single child process (because PID 1 has signals blocked)
in its own session, reaps zombies until the child exits, then
reboots the system (or powers off with -p, or restarts the child with -r).
#define FOR_oneit
#include "toys.h"
#include <sys/reboot.h>
char *console;
// The minimum amount of work necessary to get ctrl-c and such to work is:
// - Fork a child (PID 1 is special: can't exit, has various signals blocked).
// - Do a setsid() (so we have our own session).
// - In the child, attach stdio to /dev/tty0 (/dev/console is special)
// - Exec the rest of the command line.
// PID 1 then reaps zombies until the child process it spawned exits, at which
// point it calls sync() and reboot(). I could stick a kill -1 in there.
// Perform actions in response to signals. (Only root can send us signals.)
static void oneit_signaled(int signal)
int action = RB_AUTOBOOT;
toys.signal = signal;
if (signal == SIGUSR1) action = RB_HALT_SYSTEM;
if (signal == SIGUSR2) action = RB_POWER_OFF;
// PID 1 can't call reboot() because it kills the task that calls it,
// which causes the kernel to panic before the actual reboot happens.
if (!vfork()) reboot(action);
void oneit_main(void)
int i, pid, pipes[] = {SIGUSR1, SIGUSR2, SIGTERM, SIGINT};
if (FLAG_3) {
// Ensure next available filehandle is #3
while (open("/", 0) < 3);
if (pipe(pipes)) perror_exit("pipe");
fcntl(4, F_SETFD, FD_CLOEXEC);
// Setup signal handlers for signals of interest
for (i = 0; i<ARRAY_LEN(pipes); i++) xsignal(pipes[i], oneit_signaled);
while (!toys.signal) {
// Create a new child process.
pid = vfork();
if (pid) {
// pid 1 reaps zombies until it gets its child, then halts system.
// We ignore the return value of write (what would we do with it?)
// but save it in a variable we never read to make fortify shut up.
// (Real problem is if pid2 never reads, write() fills pipe and blocks.)
while (pid != wait(&i)) if (FLAG_3) i = write(4, &pid, 4);
if (toys.optflags & FLAG_n) continue;
oneit_signaled((toys.optflags & FLAG_p) ? SIGUSR2 : SIGTERM);
} else {
// Redirect stdio to /dev/tty0, with new session ID, so ctrl-c works.
for (i=0; i<3; i++) {
// Remember, O_CLOEXEC is backwards for xopen()
xopen(TT.console ? TT.console : "/dev/tty0", O_RDWR|O_CLOEXEC);
// Can't xexec() here, we vforked so we don't want to error_exit().
execvp(*toys.optargs, toys.optargs);
perror_msg("%s not in PATH=%s", *toys.optargs, getenv("PATH"));
// Give reboot() time to kick in, or avoid rapid spinning if exec failed