/* vi: set sw=4 ts=4: */ /* * Copyright (c) 2007 Denys Vlasenko <vda.linux@googlemail.com> * * Licensed under GPLv2, see file LICENSE in this source tree. */ #include "libbb.h" //applet:IF_CTTYHACK(APPLET(cttyhack, BB_DIR_BIN, BB_SUID_DROP)) //kbuild:lib-$(CONFIG_CTTYHACK) += cttyhack.o //config:config CTTYHACK //config: bool "cttyhack" //config: default y //config: help //config: One common problem reported on the mailing list is the "can't //config: access tty; job control turned off" error message, which typically //config: appears when one tries to use a shell with stdin/stdout on //config: /dev/console. //config: This device is special - it cannot be a controlling tty. //config: //config: The proper solution is to use the correct device instead of //config: /dev/console. //config: //config: cttyhack provides a "quick and dirty" solution to this problem. //config: It analyzes stdin with various ioctls, trying to determine whether //config: it is a /dev/ttyN or /dev/ttySN (virtual terminal or serial line). //config: On Linux it also checks sysfs for a pointer to the active console. //config: If cttyhack is able to find the real console device, it closes //config: stdin/out/err and reopens that device. //config: Then it executes the given program. Opening the device will make //config: that device a controlling tty. This may require cttyhack //config: to be a session leader. //config: //config: Example for /etc/inittab (for busybox init): //config: //config: ::respawn:/bin/cttyhack /bin/sh //config: //config: Starting an interactive shell from boot shell script: //config: //config: setsid cttyhack sh //config: //config: Giving controlling tty to shell running with PID 1: //config: //config: # exec cttyhack sh //config: //config: Without cttyhack, you need to know exact tty name, //config: and do something like this: //config: //config: # exec setsid sh -c 'exec sh </dev/tty1 >/dev/tty1 2>&1' //config: //config: Starting getty on a controlling tty from a shell script: //config: //config: # getty 115200 $(cttyhack) //usage:#define cttyhack_trivial_usage //usage: "[PROG ARGS]" //usage:#define cttyhack_full_usage "\n\n" //usage: "Give PROG a controlling tty if possible." //usage: "\nExample for /etc/inittab (for busybox init):" //usage: "\n ::respawn:/bin/cttyhack /bin/sh" //usage: "\nGiving controlling tty to shell running with PID 1:" //usage: "\n $ exec cttyhack sh" //usage: "\nStarting interactive shell from boot shell script:" //usage: "\n setsid cttyhack sh" #if !defined(__linux__) && !defined(TIOCGSERIAL) && !ENABLE_WERROR # warning cttyhack will not be able to detect a controlling tty on this system #endif /* From <linux/vt.h> */ struct vt_stat { unsigned short v_active; /* active vt */ unsigned short v_signal; /* signal to send */ unsigned short v_state; /* vt bitmask */ }; enum { VT_GETSTATE = 0x5603 }; /* get global vt state info */ /* From <linux/serial.h> */ struct serial_struct { int type; int line; unsigned int port; int irq; int flags; int xmit_fifo_size; int custom_divisor; int baud_base; unsigned short close_delay; char io_type; char reserved_char[1]; int hub6; unsigned short closing_wait; /* time to wait before closing */ unsigned short closing_wait2; /* no longer used... */ unsigned char *iomem_base; unsigned short iomem_reg_shift; unsigned int port_high; unsigned long iomap_base; /* cookie passed into ioremap */ int reserved[1]; }; int cttyhack_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; int cttyhack_main(int argc UNUSED_PARAM, char **argv) { int fd; char console[sizeof(int)*3 + 16]; union { struct vt_stat vt; struct serial_struct sr; char paranoia[sizeof(struct serial_struct) * 3]; } u; strcpy(console, "/dev/tty"); fd = open(console, O_RDWR); if (fd < 0) { /* We don't have ctty (or don't have "/dev/tty" node...) */ do { #ifdef __linux__ /* Note that this method does not use _stdin_. * Thus, "cttyhack </dev/something" can't be used. * However, this method is more reliable than * TIOCGSERIAL check, which assumes that all * serial lines follow /dev/ttySn convention - * which is not always the case. * Therefore, we use this method first: */ int s = open_read_close("/sys/class/tty/console/active", console + 5, sizeof(console) - 5); if (s > 0) { char *last; /* Found active console via sysfs (Linux 2.6.38+). * It looks like "[tty0 ]ttyS0\n" so zap the newline: */ console[4 + s] = '\0'; /* If there are multiple consoles, * take the last one: */ last = strrchr(console + 5, ' '); if (last) overlapping_strcpy(console + 5, last + 1); break; } if (ioctl(0, VT_GETSTATE, &u.vt) == 0) { /* this is linux virtual tty */ sprintf(console + 8, "S%u" + 1, (int)u.vt.v_active); break; } #endif #ifdef TIOCGSERIAL if (ioctl(0, TIOCGSERIAL, &u.sr) == 0) { /* this is a serial console; assuming it is named /dev/ttySn */ sprintf(console + 8, "S%u", (int)u.sr.line); break; } #endif /* nope, could not find it */ console[0] = '\0'; } while (0); } argv++; if (!argv[0]) { if (!console[0]) return EXIT_FAILURE; puts(console); return EXIT_SUCCESS; } if (fd < 0) { fd = open_or_warn(console, O_RDWR); if (fd < 0) goto ret; } //bb_error_msg("switching to '%s'", console); dup2(fd, 0); dup2(fd, 1); dup2(fd, 2); while (fd > 2) close(fd--); /* Some other session may have it as ctty, * try to steal it from them: */ ioctl(0, TIOCSCTTY, 1); ret: BB_EXECVP_or_die(argv); }