xref: /f-stack/tools/libutil/pty.3 (revision 22ce4aff)

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.Dd June 2, 2018
.Dt PTY 3
.Os
.Sh NAME
.Nm openpty ,
.Nm forkpty
.Nd auxiliary functions to obtain a pseudo-terminal
.Sh LIBRARY
.Lb libutil
.Sh SYNOPSIS
.In sys/types.h
.In sys/ioctl.h
.In termios.h
.In libutil.h
.Ft int
.Fn openpty "int *amaster" "int *aslave" "char *name" "struct termios *termp" "struct winsize *winp"
.Ft int
.Fn forkpty "int *amaster" "char *name" "struct termios *termp" "struct winsize *winp"
.Sh DESCRIPTION
The function
.Fn openpty
attempts to obtain the next available pseudo-terminal from the system (see
.Xr pty 4 ) .
If it successfully finds one, it subsequently changes the
ownership of the slave device to the real UID of the current process,
the group membership to the group
.Dq tty
(if such a group exists in the system), the access permissions for
reading and writing by the owner, and for writing by the group, and
invalidates any current use of the line by calling
.Xr revoke 2 .
.Pp
If the argument
.Fa name
is not
.Dv NULL ,
.Fn openpty
copies the pathname of the slave pty to this area.
The caller is
responsible for allocating the required space in this array.
.Pp
If the arguments
.Fa termp
or
.Fa winp
are not
.Dv NULL ,
.Fn openpty
initializes the termios and window size settings from the structures
these arguments point to, respectively.
.Pp
Upon return, the open file descriptors for the master and slave side
of the pty are returned in the locations pointed to by
.Fa amaster
and
.Fa aslave ,
respectively.
.Pp
The
.Fn forkpty
function first calls
.Fn openpty
to obtain the next available pseudo-terminal from the system.
Upon success,
it forks off a new process.
In the child process, it closes the descriptor
for the master side of the pty, and calls
.Xr login_tty 3
for the slave pty.
In the parent process, it closes the descriptor for the
slave side of the pty.
The arguments
.Fa amaster ,
.Fa name ,
.Fa termp ,
and
.Fa winp
have the same meaning as described for
.Fn openpty .
.Sh RETURN VALUES
The
.Fn openpty
function returns 0 on success, or -1 on failure.
.Pp
The
.Fn forkpty
function returns -1 on failure, 0 in the slave process, and the process ID of
the slave process in the parent process.
.Sh ERRORS
The
.Fn openpty
function may fail and set the global variable
.Dv errno
for any of the errors specified for the
.Xr grantpt 3 ,
.Xr posix_openpt 2 ,
.Xr ptsname 3 ,
and
.Xr unlockpt 3
functions and the
.Xr revoke 2
system call.
.Pp
In addition to this,
.Fn forkpty
may set it to any value as described for
.Xr fork 2 .
.Sh SEE ALSO
.Xr chmod 2 ,
.Xr chown 2 ,
.Xr fork 2 ,
.Xr getuid 2 ,
.Xr open 2 ,
.Xr revoke 2 ,
.Xr login_tty 3 ,
.Xr pty 4 ,
.Xr termios 4 ,
.Xr group 5
.Sh HISTORY
The
.Fn openpty
and
.Fn forkpty
functions first appeared in
.Bx 4.3 Reno.
.Sh BUGS
.Fn openpty
writes the slave terminal's name to
.Fa name ,
but does not check that sufficient space is available.
It is advisable to use
.Xr ptsname 3
instead.