tcgetsid - get session ID

       For an explanation of the terms used in this section, see attributes(7).
       ┌─────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                                                                   │ Attribute     │ Value   │
       ├─────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │ tcgetsid()                                                                  │ Thread safety │ MT-Safe │
       └─────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

       The function tcgetsid() returns the session ID of the current session that has the terminal associated to
       fd as controlling terminal.  This terminal must be the controlling terminal of the calling process.

EBADFfd is not a valid file descriptor.

       ENOTTY The calling process does not have a controlling terminal, or it has one but it is not described by
              fd.

       glibc 2.1.  POSIX.1-2001.

       This function is implemented via the TIOCGSIDioctl(2), present since Linux 2.1.71.

       Standard C library (libc, -lc)

       tcgetsid - get session ID

       When  fd  refers  to  the  controlling  terminal  of our session, the function tcgetsid() will return the
       session ID of this session.  Otherwise, -1 is returned, and errno is set to indicate the error.

getsid(2)

Linux man-pages 6.9.1                              2024-05-02                                        tcgetsid(3)

       POSIX.1-2008.

#define_XOPEN_SOURCE500        /* See feature_test_macros(7) */
       #include<termios.h>pid_ttcgetsid(intfd);