How to Obtain Pseudo Terminal Master file descriptor from inside ssh session?

Question

in C or bash,

I was wondering how, if possible, do you obtain from inside an ssh session, the file descriptor to the pseudo terminal master responsible for getting input to that's session's slave(pts).

Answer 1

The shell process has no master file descriptor, only slave.

The shell's parent process (be it sshd or xterm or screen or whatever) creates a new master by calling getpt(3) or posix_openpt(3). The function returns the master file descriptor. The parent process then obtains the slave file descriptor by calling a combination of grantpt(3), unlockpt(3), ptsname(3) and open(2). This is for Linux and other POSIXized systems, other *nixes may use other functions, but the net result is the same. The parent process has the master/slave pair of file descriptors.

The slave descriptor, and the slave descriptor only, is then passed to the shell as its standard input, output and error.

Answer 2

From Solaris 5.8 PTS(7D) Man-page - STREAMS pseudo-tty slave driver

Only one open is allowed on a master device.

I guess that answers my question :)
EDIT: actually it does not, because if there is a way to obtain the file descriptor, i won't need to open again, it is a file descriptor lol , no need to open

Answer 3

On unix-based systems, you can open the controlling terminal of the current process by opening /dev/tty. In many cases your program will already have this open as stdin, stdout and stderr, but even if your program is being invoked with stdin, stdout or stderr redirected, /dev/tty will give you the controlling terminal of the process.