xref: /freebsd/lib/libutil/pty.3 (revision 1130b656e5fe4c2d1ba299e024d1b40eaeebd380)
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2.\" Copyright (c) 1996 Joerg Wunsch
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26.\" $FreeBSD$
27.\" "
28.Dd December 29, 1996
29.Os
30.Dt PTY 3
31.Sh NAME
32.Nm openpty ,
33.Nm forkpty
34.Nd auxiliary functions to obtain a pseudo-terminal
35.Sh SYNOPSIS
36.Fd #include <sys/types.h>
37.Fd #include <sys/ioctl.h>
38.Fd #include <termios.h>
39.Fd #include <libutil.h>
40.Ft int
41.Fn openpty "int *amaster" "int *aslave" "char *name" "struct termios *termp" "struct winsize *winp"
42.Ft int
43.Fn forkpty "int *amaster" "char *name" "struct termios *termp" "struct winsize *winp"
44.Pp
45Link with
46.Va -lutil
47on the
48.Xr cc 1
49command line.
50.Sh DESCRIPTION
51The function
52.Fn openpty
53attempts to obtain the next available pseudo-terminal from the system (see
54.Xr pty 4 ) .
55If it successfully finds one, it subsequently tries to change the
56ownership of the slave device to the real UID of the current process,
57the group membership to the group
58.Dq tty
59(if such a group exists in the system), the access permissions for
60reading and writing by the owner, and for writing by the group, and to
61invalidate any current use of the line by calling
62.Xr revoke 2 .
63.Pp
64If the argument
65.Fa name
66is not
67.Dv NULL ,
68.Fn openpty
69copies the pathname of the slave pty to this area.  The caller is
70responsible for allocating the required space in this array.
71.Pp
72If the arguments
73.Fa termp
74or
75.Fa winp
76are not
77.Dv NULL ,
78.Fn openpty
79initializes the termios and window size settings from the structures
80these arguments point to, respectively.
81.Pp
82Upon return, the open file descriptors for the master and slave side
83of the pty are returned in the locations pointed to by
84.Fa amaster
85and
86.Fa aslave ,
87respectively.
88.Pp
89.Fn Forkpty
90first calls
91.Fn openpty
92to obtain the next available pseudo-terminal from the system.  Upon success,
93it forks off a new process.  In the child process, it closes the descriptor
94for the master side of the pty, and calls
95.Xr login_tty 3
96for the slave pty.  In the parent process, it closes the descriptor for the
97slave side of the pty.  The arguments
98.Fa amaster ,
99.Fa name ,
100.Fa termp ,
101and
102.Fa winp
103have the same meaning as described for
104.Fn openpty .
105.Sh RETURN VALUES
106.Fn Openpty
107returns 0 on success, or -1 on failure.
108.Pp
109.Fn Forkpty
110returns -1 on failure, 0 in the slave process, and the process ID of the
111slave process in the parent process.
112.Sh ERRORS
113On failure,
114.Fn openpty
115will set the global variable
116.Dv errno
117to
118.Er ENOENT .
119.Pp
120In addition to this,
121.Fn forkpty
122may set it to any value as described for
123.Xr fork 2 .
124.Sh SEE ALSO
125.Xr chmod 2 ,
126.Xr chown 2 ,
127.Xr fork 2 ,
128.Xr getuid 2 ,
129.Xr open 2 ,
130.Xr revoke 2 ,
131.Xr login_tty 3 ,
132.Xr termios 3 ,
133.Xr pty 4 ,
134.Xr group 5
135.Sh BUGS
136The calling process must have an effective UID of super-user in order
137to perform all the intended actions.  No notification will occur if
138.Fn openpty
139or
140.Fn forkpty
141failed to proceed with one of the described steps, as long as they could
142at least allocate the pty at all (and create the new process in the case
143of
144.Fn forkpty ) .
145