1 | /* vi: set sw=4 ts=4: */
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2 | /*
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3 | * Copyright (c) 2007 Denys Vlasenko <vda.linux@googlemail.com>
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4 | *
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5 | * Licensed under GPLv2, see file LICENSE in this source tree.
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6 | */
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7 | #include "libbb.h"
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8 |
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9 | //applet:IF_CTTYHACK(APPLET(cttyhack, BB_DIR_BIN, BB_SUID_DROP))
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10 |
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11 | //kbuild:lib-$(CONFIG_CTTYHACK) += cttyhack.o
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12 |
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13 | //config:config CTTYHACK
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14 | //config: bool "cttyhack"
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15 | //config: default y
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16 | //config: help
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17 | //config: One common problem reported on the mailing list is the "can't
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18 | //config: access tty; job control turned off" error message, which typically
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19 | //config: appears when one tries to use a shell with stdin/stdout on
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20 | //config: /dev/console.
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21 | //config: This device is special - it cannot be a controlling tty.
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22 | //config:
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23 | //config: The proper solution is to use the correct device instead of
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24 | //config: /dev/console.
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25 | //config:
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26 | //config: cttyhack provides a "quick and dirty" solution to this problem.
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27 | //config: It analyzes stdin with various ioctls, trying to determine whether
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28 | //config: it is a /dev/ttyN or /dev/ttySN (virtual terminal or serial line).
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29 | //config: On Linux it also checks sysfs for a pointer to the active console.
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30 | //config: If cttyhack is able to find the real console device, it closes
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31 | //config: stdin/out/err and reopens that device.
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32 | //config: Then it executes the given program. Opening the device will make
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33 | //config: that device a controlling tty. This may require cttyhack
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34 | //config: to be a session leader.
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35 | //config:
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36 | //config: Example for /etc/inittab (for busybox init):
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37 | //config:
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38 | //config: ::respawn:/bin/cttyhack /bin/sh
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39 | //config:
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40 | //config: Starting an interactive shell from boot shell script:
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41 | //config:
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42 | //config: setsid cttyhack sh
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43 | //config:
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44 | //config: Giving controlling tty to shell running with PID 1:
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45 | //config:
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46 | //config: # exec cttyhack sh
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47 | //config:
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48 | //config: Without cttyhack, you need to know exact tty name,
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49 | //config: and do something like this:
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50 | //config:
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51 | //config: # exec setsid sh -c 'exec sh </dev/tty1 >/dev/tty1 2>&1'
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52 | //config:
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53 | //config: Starting getty on a controlling tty from a shell script:
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54 | //config:
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55 | //config: # getty 115200 $(cttyhack)
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56 |
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57 | //usage:#define cttyhack_trivial_usage
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58 | //usage: "[PROG ARGS]"
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59 | //usage:#define cttyhack_full_usage "\n\n"
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60 | //usage: "Give PROG a controlling tty if possible."
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61 | //usage: "\nExample for /etc/inittab (for busybox init):"
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62 | //usage: "\n ::respawn:/bin/cttyhack /bin/sh"
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63 | //usage: "\nGiving controlling tty to shell running with PID 1:"
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64 | //usage: "\n $ exec cttyhack sh"
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65 | //usage: "\nStarting interactive shell from boot shell script:"
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66 | //usage: "\n setsid cttyhack sh"
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67 |
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68 | #if !defined(__linux__) && !defined(TIOCGSERIAL) && !ENABLE_WERROR
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69 | # warning cttyhack will not be able to detect a controlling tty on this system
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70 | #endif
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71 |
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72 | /* From <linux/vt.h> */
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73 | struct vt_stat {
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74 | unsigned short v_active; /* active vt */
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75 | unsigned short v_signal; /* signal to send */
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76 | unsigned short v_state; /* vt bitmask */
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77 | };
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78 | enum { VT_GETSTATE = 0x5603 }; /* get global vt state info */
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79 |
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80 | /* From <linux/serial.h> */
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81 | struct serial_struct {
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82 | int type;
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83 | int line;
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84 | unsigned int port;
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85 | int irq;
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86 | int flags;
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87 | int xmit_fifo_size;
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88 | int custom_divisor;
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89 | int baud_base;
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90 | unsigned short close_delay;
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91 | char io_type;
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92 | char reserved_char[1];
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93 | int hub6;
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94 | unsigned short closing_wait; /* time to wait before closing */
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95 | unsigned short closing_wait2; /* no longer used... */
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96 | unsigned char *iomem_base;
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97 | unsigned short iomem_reg_shift;
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98 | unsigned int port_high;
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99 | unsigned long iomap_base; /* cookie passed into ioremap */
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100 | int reserved[1];
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101 | };
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102 |
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103 | int cttyhack_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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104 | int cttyhack_main(int argc UNUSED_PARAM, char **argv)
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105 | {
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106 | int fd;
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107 | char console[sizeof(int)*3 + 16];
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108 | union {
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109 | struct vt_stat vt;
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110 | struct serial_struct sr;
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111 | char paranoia[sizeof(struct serial_struct) * 3];
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112 | } u;
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113 |
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114 | strcpy(console, "/dev/tty");
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115 | fd = open(console, O_RDWR);
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116 | if (fd < 0) {
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117 | /* We don't have ctty (or don't have "/dev/tty" node...) */
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118 | do {
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119 | #ifdef __linux__
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120 | /* Note that this method does not use _stdin_.
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121 | * Thus, "cttyhack </dev/something" can't be used.
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122 | * However, this method is more reliable than
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123 | * TIOCGSERIAL check, which assumes that all
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124 | * serial lines follow /dev/ttySn convention -
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125 | * which is not always the case.
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126 | * Therefore, we use this method first:
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127 | */
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128 | int s = open_read_close("/sys/class/tty/console/active",
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129 | console + 5, sizeof(console) - 5);
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130 | if (s > 0) {
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131 | char *last;
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132 | /* Found active console via sysfs (Linux 2.6.38+).
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133 | * It looks like "[tty0 ]ttyS0\n" so zap the newline:
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134 | */
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135 | console[4 + s] = '\0';
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136 | /* If there are multiple consoles,
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137 | * take the last one:
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138 | */
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139 | last = strrchr(console + 5, ' ');
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140 | if (last)
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141 | overlapping_strcpy(console + 5, last + 1);
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142 | break;
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143 | }
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144 |
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145 | if (ioctl(0, VT_GETSTATE, &u.vt) == 0) {
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146 | /* this is linux virtual tty */
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147 | sprintf(console + 8, "S%u" + 1, (int)u.vt.v_active);
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148 | break;
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149 | }
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150 | #endif
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151 | #ifdef TIOCGSERIAL
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152 | if (ioctl(0, TIOCGSERIAL, &u.sr) == 0) {
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153 | /* this is a serial console; assuming it is named /dev/ttySn */
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154 | sprintf(console + 8, "S%u", (int)u.sr.line);
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155 | break;
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156 | }
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157 | #endif
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158 | /* nope, could not find it */
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159 | console[0] = '\0';
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160 | } while (0);
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161 | }
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162 |
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163 | argv++;
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164 | if (!argv[0]) {
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165 | if (!console[0])
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166 | return EXIT_FAILURE;
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167 | puts(console);
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168 | return EXIT_SUCCESS;
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169 | }
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170 |
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171 | if (fd < 0) {
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172 | fd = open_or_warn(console, O_RDWR);
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173 | if (fd < 0)
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174 | goto ret;
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175 | }
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176 | //bb_error_msg("switching to '%s'", console);
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177 | dup2(fd, 0);
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178 | dup2(fd, 1);
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179 | dup2(fd, 2);
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180 | while (fd > 2)
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181 | close(fd--);
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182 | /* Some other session may have it as ctty,
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183 | * try to steal it from them:
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184 | */
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185 | ioctl(0, TIOCSCTTY, 1);
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186 | ret:
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187 | BB_EXECVP_or_die(argv);
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188 | }
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