1OPENPTY(3) Linux Programmer's Manual OPENPTY(3)
2
6 openpty, login_tty, forkpty - terminal utility functions
7
9 #include <pty.h>
10 int openpty(int *amaster, int *aslave, char *name,
12 const struct termios *termp,
13 const struct winsize *winp);
14 pid_t forkpty(int *amaster, char *name,
15 const struct termios *termp,
16 const struct winsize *winp);
17 #include <utmp.h>
19 int login_tty(int fd);
21 Link with -lutil.
23
25 The openpty() function finds an available pseudoterminal and returns
26 file descriptors for the master and slave in amaster and aslave. If
27 name is not NULL, the filename of the slave is returned in name. If
28 termp is not NULL, the terminal parameters of the slave will be set to
29 the values in termp. If winp is not NULL, the window size of the slave
30 will be set to the values in winp.
31 The login_tty() function prepares for a login on the terminal referred
33 to by the file descriptor fd (which may be a real terminal device, or
34 the slave of a pseudoterminal as returned by openpty()) by creating a
35 new session, making fd the controlling terminal for the calling
36 process, setting fd to be the standard input, output, and error streams
37 of the current process, and closing fd.
38 The forkpty() function combines openpty(), fork(2), and login_tty() to
40 create a new process operating in a pseudoterminal. A file descriptor
41 referring to master side of the pseudoterminal is returned in amaster.
42 If name is not NULL, the buffer it points to is used to return the
43 filename of the slave. The termp and winp arguments, if not NULL, will
44 determine the terminal attributes and window size of the slave side of
45 the pseudoterminal.
46
48 If a call to openpty(), login_tty(), or forkpty() is not successful, -1
49 is returned and errno is set to indicate the error. Otherwise,
50 openpty(), login_tty(), and the child process of forkpty() return 0,
51 and the parent process of forkpty() returns the process ID of the child
52 process.
53
55 openpty() fails if:
56 ENOENT There are no available terminals.
58 login_tty() fails if ioctl(2) fails to set fd to the controlling termi‐
60 nal of the calling process.
61 forkpty() fails if either openpty() or fork(2) fails.
63
65 For an explanation of the terms used in this section, see at‐
66 tributes(7).
67 ┌─────────────────────────────┬───────────────┬────────────────────────┐
69 │Interface │ Attribute │ Value │
70 ├─────────────────────────────┼───────────────┼────────────────────────┤
71 │forkpty(), openpty() │ Thread safety │ MT-Safe locale │
72 ├─────────────────────────────┼───────────────┼────────────────────────┤
73 │login_tty() │ Thread safety │ MT-Unsafe race:ttyname │
74 └─────────────────────────────┴───────────────┴────────────────────────┘
75
77 These are BSD functions, present in glibc. They are not standardized
78 in POSIX.
79
81 The const modifiers were added to the structure pointer arguments of
82 openpty() and forkpty() in glibc 2.8.
83 In versions of glibc before 2.0.92, openpty() returns file descriptors
85 for a BSD pseudoterminal pair; since glibc 2.0.92, it first attempts to
86 open a UNIX 98 pseudoterminal pair, and falls back to opening a BSD
87 pseudoterminal pair if that fails.
88
90 Nobody knows how much space should be reserved for name. So, calling
91 openpty() or forkpty() with non-NULL name may not be secure.
92
94 fork(2), ttyname(3), pty(7)
95
97 This page is part of release 5.12 of the Linux man-pages project. A
98 description of the project, information about reporting bugs, and the
99 latest version of this page, can be found at
100 https://www.kernel.org/doc/man-pages/.
101GNU 2021-03-22 OPENPTY(3)