man3/openpty.3

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  30 .\" Converted into a manpage again by Martin Schulze <joey@infodrom.org>
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  32 .\" Added -lutil remark, 030718
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  34 .TH OPENPTY 3  2017-09-15 "GNU" "Linux Programmer's Manual"
  35 .SH NAME
  36 openpty, login_tty, forkpty \- terminal utility functions
  37 .SH SYNOPSIS
  38 .nf
  39 .B #include <pty.h>
  40 .PP
  41 .BI "int openpty(int *" amaster ", int *" aslave ", char *" name ,
  42 .BI "            const struct termios *" termp ,
  43 .BI "            const struct winsize *" winp );
  44 .PP
  45 .BI "pid_t forkpty(int *" amaster ", char *" name ,
  46 .BI "              const struct termios *" termp ,
  47 .BI "              const struct winsize *" winp );
  48
  49 .B #include <utmp.h>
  50 .PP
  51 .BI "int login_tty(int " fd );
  52 .PP
  53 Link with \fI\-lutil\fP.
  54 .fi
  55 .SH DESCRIPTION
  56 The
  57 .BR openpty ()
  58 function finds an available pseudoterminal and returns file descriptors
  59 for the master and slave in
  60 .I amaster
  61 and
  62 .IR aslave .
  63 If
  64 .I name
  65 is not NULL, the filename of the slave is returned in
  66 .IR name .
  67 If
  68 .I termp
  69 is not NULL, the terminal parameters of the slave will be set to the
  70 values in
  71 .IR termp .
  72 If
  73 .I winp
  74 is not NULL, the window size of the slave will be set to the values in
  75 .IR winp .
  76 .PP
  77 The
  78 .BR login_tty ()
  79 function prepares for a login on the terminal
  80 .I fd
  81 (which may be a real terminal device, or the slave of a pseudoterminal as
  82 returned by
  83 .BR openpty ())
  84 by creating a new session, making
  85 .I fd
  86 the controlling terminal for the calling process, setting
  87 .I fd
  88 to be the standard input, output, and error streams of the current
  89 process, and closing
  90 .IR fd .
  91 .PP
  92 The
  93 .BR forkpty ()
  94 function combines
  95 .BR openpty (),
  96 .BR fork (2),
  97 and
  98 .BR login_tty ()
  99 to create a new process operating in a pseudoterminal.
 100 The file
 101 descriptor of the master side of the pseudoterminal is returned in
 102 .IR amaster .
 103 If
 104 .I name
 105 is not NULL, the buffer it points to is used to return the
 106 filename of the slave.
 107 The
 108 .I termp
 109 and
 110 .I winp
 111 arguments, if not NULL,
 112 will determine the terminal attributes and window size of the slave
 113 side of the pseudoterminal.
 114 .SH RETURN VALUE
 115 If a call to
 116 .BR openpty (),
 117 .BR login_tty (),
 118 or
 119 .BR forkpty ()
 120 is not successful, \-1 is returned and
 121 .I errno
 122 is set to indicate the error.
 123 Otherwise,
 124 .BR openpty (),
 125 .BR login_tty (),
 126 and the child process of
 127 .BR forkpty ()
 128 return 0, and the parent process of
 129 .BR forkpty ()
 130 returns the process ID of the child process.
 131 .SH ERRORS
 132 .BR openpty ()
 133 fails if:
 134 .TP
 135 .B ENOENT
 136 There are no available terminals.
 137 .PP
 138 .BR login_tty ()
 139 fails if
 140 .BR ioctl (2)
 141 fails to set
 142 .I fd
 143 to the controlling terminal of the calling process.
 144 .PP
 145 .BR forkpty ()
 146 fails if either
 147 .BR openpty ()
 148 or
 149 .BR fork (2)
 150 fails.
 151 .SH ATTRIBUTES
 152 For an explanation of the terms used in this section, see
 153 .BR attributes (7).
 154 .TS
 155 allbox;
 156 lbw20 lb lb
 157 l l l.
 158 Interface       Attribute       Value
 159 T{
 160 .BR forkpty (),
 161 .BR openpty ()
 162 T}      Thread safety   MT-Safe locale
 163 T{
 164 .BR login_tty ()
 165 T}      Thread safety   MT-Unsafe race:ttyname
 166 .TE
 167 .sp 1
 168 .SH CONFORMING TO
 169 These are BSD functions, present in glibc.
 170 They are not standardized in POSIX.
 171 .SH NOTES
 172 The
 173 .B const
 174 modifiers were added to the structure pointer arguments of
 175 .BR openpty ()
 176 and
 177 .BR forkpty ()
 178 in glibc 2.8.
 179 .PP
 180 In versions of glibc before 2.0.92,
 181 .BR openpty ()
 182 returns file descriptors for a BSD pseudoterminal pair;
 183 since glibc 2.0.92,
 184 it first attempts to open a UNIX 98 pseudoterminal pair,
 185 and falls back to opening a BSD pseudoterminal pair if that fails.
 186 .SH BUGS
 187 Nobody knows how much space should be reserved for
 188 .IR name .
 189 So, calling
 190 .BR openpty ()
 191 or
 192 .BR forkpty ()
 193 with non-NULL
 194 .I name
 195 may not be secure.
 196 .SH SEE ALSO
 197 .BR fork (2),
 198 .BR ttyname (3),
 199 .BR pty (7)