TCSETPGRP(3P)

💅 TCSETPGRP(3P) — bestie edition 💅

okay so this one's from the POSIX Programmer's Manual, and before we even get into it, here's the lil heads-up that comes with every page in this set:

🫶 PROLOG 🫶

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

ngl that's the standard disclaimer and it's lowkey important — don't come for me if Linux does its own thing, okay? check the Linux page. 🙈

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✨ NAME ✨

tcsetpgrp — set the foreground process group ID

periodt, that's the whole job. it sets the foreground process group ID. 💅

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🌸 SYNOPSIS 🌸

#include <unistd.h>

int tcsetpgrp(int fildes, pid_t pgid_id);

two args, one int coming back at you. we love a tidy signature. 🎀

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💖 DESCRIPTION 💖

okay so here's the tea. If the process has a controlling terminal, tcsetpgrp() shall set the foreground process group ID associated with the terminal to pgid_id.

but bestie, there are rules, and the application shall ensure them, not the function. so like, you gotta check yourself:

• the file associated with fildes is the controlling terminal of the calling process, AND
• that controlling terminal is currently associated with the session of the calling process, AND
• the value of pgid_id matches a process group ID of a process in the same session as the calling process.

three vibes. all required. no skipping. ✋

now for the spicy part 🌶️ — Attempts to use tcsetpgrp() from a process which is a member of a background process group on a fildes associated with its controlling terminal shall cause the process group to be sent a SIGTTOU signal.

like, it's giving "who do you think you are, background process?" 😭

BUT. and this is the iconic loophole: If the calling thread is blocking SIGTTOU signals or the process is ignoring SIGTTOU signals, the process shall be allowed to perform the operation, and no signal is sent. so if you're already ghosting SIGTTOU, it just lets you cook. 🔥

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👑 RETURN VALUE 👑

Upon successful completion, 0 shall be returned. Otherwise, -1 shall be returned and errno set to indicate the error.

zero = slay. negative one = check errno, bestie. 💀

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🦋 ERRORS 🦋

The tcsetpgrp() function shall fail if:

• EBADF — The fildes argument is not a valid file descriptor.
• EINVAL — This implementation does not support the value in the pgid_id argument.
• EIO — The process group of the writing process is orphaned, the calling thread is not blocking SIGTTOU, and the process is not ignoring SIGTTOU.
• ENOTTY — The calling process does not have a controlling terminal, or the file is not the controlling terminal, or the controlling terminal is no longer associated with the session of the calling process.
• EPERM — The value of pgid_id is a value supported by the implementation, but does not match the process group ID of a process in the same session as the calling process.

EIO is the orphaned-process-group one and it's kinda dramatic ngl — no controlling tty parent, not blocking SIGTTOU, not ignoring it… it's giving abandoned. 😭

The following sections are informative.

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🌈 EXAMPLES 🌈

None.

not me having nothing to show you. 🙈 the standard just said "no examples, figure it out bestie."

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🧚 APPLICATION USAGE 🧚

None.

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💜 RATIONALE 💜

None.

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⭐ FUTURE DIRECTIONS ⭐

None.

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🍓 SEE ALSO 🍓

• tcgetpgrp()
• The Base Definitions volume of POSIX.1‐2017, <sys_types.h>, <unistd.h>

iykyk — tcgetpgrp() is literally the mirror of this one. read them together. 🫶

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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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and that's the whole page, bestie!! 💖 brought to you by IEEE/The Open Group, 2017 — yes the date is literally just 2017, iconic of them. go set that foreground process group, you absolute main character. 👑✨💅