POSIX_OPENPT(3)            POSIX Programmer's Manual           POSIX_OPENPT(3)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       posix_openpt -- open a pseudo-terminal device

SSYYNNOOPPSSIISS
       #include <stdlib.h>
       #include <fcntl.h>

       int posix_openpt(int _o_f_l_a_g);

DDEESSCCRRIIPPTTIIOONN
       The _p_o_s_i_x___o_p_e_n_p_t() function shall establish a connection between a
       master device for a pseudo-terminal and a file descriptor. The file
       descriptor shall be allocated as described in _S_e_c_t_i_o_n _2_._1_4, _F_i_l_e
       _D_e_s_c_r_i_p_t_o_r _A_l_l_o_c_a_t_i_o_n and can be used by other I/O functions that refer
       to that pseudo-terminal.

       The file status flags and file access modes of the open file
       description shall be set according to the value of _o_f_l_a_g.

       Values for _o_f_l_a_g are constructed by a bitwise-inclusive OR of flags
       from the following list, defined in _<_f_c_n_t_l_._h_>:

       O_RDWR      Open for reading and writing.

       O_NOCTTY    If set _p_o_s_i_x___o_p_e_n_p_t() shall not cause the terminal device
                   to become the controlling terminal for the process.

       The behavior of other values for the _o_f_l_a_g argument is unspecified.

RREETTUURRNN VVAALLUUEE
       Upon successful completion, the _p_o_s_i_x___o_p_e_n_p_t() function shall open a
       file descriptor for a master pseudo-terminal device and return a non-
       negative integer representing the file descriptor. Otherwise, -1 shall
       be returned and _e_r_r_n_o set to indicate the error.

EERRRROORRSS
       The _p_o_s_i_x___o_p_e_n_p_t() function shall fail if:

       EEMMFFIILLEE All file descriptors available to the process are currently
              open.

       EENNFFIILLEE The maximum allowable number of files is currently open in the
              system.

       The _p_o_s_i_x___o_p_e_n_p_t() function may fail if:

       EEIINNVVAALL The value of _o_f_l_a_g is not valid.

       EEAAGGAAIINN Out of pseudo-terminal resources.

       EENNOOSSRR  Out of STREAMS resources.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
   OOppeenniinngg aa PPsseeuuddoo--TTeerrmmiinnaall aanndd RReettuurrnniinngg tthhee NNaammee ooff tthhee SSllaavvee DDeevviiccee aanndd aa
       FFiillee DDeessccrriippttoorr
           #include <fcntl.h>
           #include <stdio.h>

           int masterfd, slavefd;
           char *slavedevice;

           masterfd = posix_openpt(O_RDWR|O_NOCTTY);

           if (masterfd == -1
               || grantpt (masterfd) == -1
               || unlockpt (masterfd) == -1
               || (slavedevice = ptsname (masterfd)) == NULL)
               return -1;

           printf("slave device is: %s\n", slavedevice);

           slavefd = open(slavedevice, O_RDWR|O_NOCTTY);
           if (slavefd < 0)
               return -1;

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       This function is a method for portably obtaining a file descriptor of a
       master terminal device for a pseudo-terminal. The _g_r_a_n_t_p_t() and
       _p_t_s_n_a_m_e() functions can be used to manipulate mode and ownership
       permissions, and to obtain the name of the slave device, respectively.

RRAATTIIOONNAALLEE
       The standard developers considered the matter of adding a special
       device for cloning master pseudo-terminals: the //ddeevv//ppttmmxx device.
       However, consensus could not be reached, and it was felt that adding a
       new function would permit other implementations. The _p_o_s_i_x___o_p_e_n_p_t()
       function is designed to complement the _g_r_a_n_t_p_t(), _p_t_s_n_a_m_e(), and
       _u_n_l_o_c_k_p_t() functions.

       On implementations supporting the //ddeevv//ppttmmxx clone device, opening the
       master device of a pseudo-terminal is simply:


           mfdp = open("/dev/ptmx", oflag );
           if (mfdp < 0)
               return -1;

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _S_e_c_t_i_o_n _2_._1_4, _F_i_l_e _D_e_s_c_r_i_p_t_o_r _A_l_l_o_c_a_t_i_o_n, _g_r_a_n_t_p_t(), _o_p_e_n(), _p_t_s_n_a_m_e(),
       _u_n_l_o_c_k_p_t()

       The Base Definitions volume of POSIX.1-2017, <<ffccnnttll..hh>>, <<ssttddlliibb..hh>>

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                      POSIX_OPENPT(3)
