/* oneit.c - tiny init replacement to launch a single child process. * * Copyright 2005, 2007 by Rob Landley <rob@landley.net>. USE_ONEIT(NEWTOY(oneit, "^<1nc:p3[!pn]", TOYFLAG_SBIN)) config ONEIT bool "oneit" default y help 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). Responds to SIGUSR1 by halting the system, SIGUSR2 by powering off, and SIGTERM or SIGINT reboot. */ #define FOR_oneit #include "toys.h" #include <sys/reboot.h> GLOBALS( 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. sync(); if (!vfork()) reboot(action); } void oneit_main(void) { int i, pid, pipes[] = {SIGUSR1, SIGUSR2, SIGTERM, SIGINT}; // Setup signal handlers for signals of interest for (i = 0; i<ARRAY_LEN(pipes); i++) xsignal(pipes[i], oneit_signaled); if (toys.optflags & FLAG_3) { // Ensure next available filehandle is #3 while (open("/", 0) < 3); close(3); close(4); if (pipe(pipes)) perror_exit("pipe"); fcntl(4, F_SETFD, FD_CLOEXEC); } 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 (toys.optflags & 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. setsid(); for (i=0; i<3; i++) { close(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(). toy_exec(toys.optargs); execvp(*toys.optargs, toys.optargs); perror_msg("%s not in PATH=%s", *toys.optargs, getenv("PATH")); break; } } // Give reboot() time to kick in, or avoid rapid spinning if exec failed sleep(5); _exit(127); }