POSIX_OPENPT(3P)

🌸 PROLOG 🌸

okay bestie, real talk before we even start: this manual page is part of the POSIX Programmer's Manual 💅. But heads up — the Linux implementation of this interface may differ (so pls consult the corresponding Linux manual page for the deets on Linux behavior), or honestly the interface may not even be implemented on Linux at all. it's giving "check your local listings" energy 😭.

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✨ NAME ✨

posix_openpt — open a pseudo-terminal device 🎀

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🦋 SYNOPSIS 🦋

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

int posix_openpt(int oflag);

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💖 DESCRIPTION 💖

so like, what does posix_openpt() actually do? it shall establish a connection between a master device for a pseudo-terminal and a file descriptor 🫶. the file descriptor shall be allocated exactly as described in Section 2.14, File Descriptor Allocation, and can be used by other I/O functions that refer to that pseudo-terminal. main character behavior fr fr.

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

values for oflag are constructed by a bitwise-inclusive OR of flags from this list, all defined in <fcntl.h>:

• O_RDWR — open for reading and writing, both, at the same time, iconic 👑
• O_NOCTTY — if set, posix_openpt() shall not cause the terminal device to become the controlling terminal for the process 🚫

⚠️ the behavior of other values for the oflag argument is unspecified. don't do it. no cap.

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🌈 RETURN VALUE 🌈

upon successful completion (slay 💅), the posix_openpt() function shall open a file descriptor for a master pseudo-terminal device and return a non-negative integer representing that file descriptor.

otherwise? -1 shall be returned and errno set to indicate the error 😭. rude but okay.

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💀 ERRORS 💀

the posix_openpt() function shall fail if:

• EMFILE — all file descriptors available to the process are currently open. no more slots bestie, we're full 🙈
• ENFILE — the maximum allowable number of files is currently open in the system. the whole system is booked and busy 😭

the posix_openpt() function may fail if:

• EINVAL — the value of oflag is not valid. you gave it a lil nonsense value and it said absolutely not 💀
• EAGAIN — out of pseudo-terminal resources. we ran out 🍓
• ENOSR — out of STREAMS resources. also ran out, different bucket 🧚

the following sections are informative.

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🎀 EXAMPLES 🎀

🦋 Opening a Pseudo-Terminal and Returning the Name of the Slave Device and a File Descriptor 🦋

#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;

look at that chain of || doing the absolute most ✨. it ate, honestly.

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💅 APPLICATION USAGE 💅

this function is a method for portably obtaining a file descriptor of a master terminal device for a pseudo-terminal 🔥.

the grantpt() and ptsname() functions can be used to manipulate mode and ownership permissions, and to obtain the name of the slave device, respectively 🫶. team effort, periodt.

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👑 RATIONALE 👑

the standard developers considered the matter of adding a special device for cloning master pseudo-terminals: the /dev/ptmx device 👀. however, consensus could not be reached 😭, and it was felt that adding a new function would permit other implementations. the posix_openpt() function is designed to complement the grantpt(), ptsname(), and unlockpt() functions — they're a little friend group, iykyk 💜.

on implementations supporting the /dev/ptmx clone device, opening the master device of a pseudo-terminal is simply:

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

so simple. so clean. so demure ✨.

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⭐ FUTURE DIRECTIONS ⭐

none. literally nothing coming. the future is a blank page bestie, we're done here 🌸.

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🌟 SEE ALSO 🌟

• Section 2.14, File Descriptor Allocation
• grantpt()
• open()
• ptsname()
• unlockpt()

the Base Definitions volume of POSIX.1‐2017: <fcntl.h>, <stdlib.h> 🦋

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🫶 COPYRIGHT 🫶

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 🐛.

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okay that's the whole thing, you're officially a pseudo-terminal girlie now 💅✨. this lil number came to you courtesy of IEEE/The Open Group, 2017, and its official glow-up name is POSIX_OPENPT(3P) — go be the main character of your own terminal session, bestie 🎀🦋💖