(03-07-2016, 12:41 PM)vain Wrote:

Quote:I tried with a terminal multiplexer, they lead back to the right terminal, so no issues on that part.

Actually, that got me thinking. Is that correct? GNU screen does indeed hold an open fd to /dev/ptmx, but my method above can't find it:

Code:

$ ls -al /proc/14731/fd
ls: cannot open directory '/proc/14731/fd': Permission denied
$ sudo !!
sudo ls -al /proc/14731/fd
total 0
dr-x------ 2 root root   0 Jul  3 16:58 .
dr-xr-xr-x 9 root users  0 Jul  3 16:58 ..
lr-x------ 1 root root  64 Jul  3 17:00 0 -> /dev/null
l-wx------ 1 root root  64 Jul  3 17:00 1 -> /dev/null
l-wx------ 1 root root  64 Jul  3 17:00 2 -> /dev/null
lrwx------ 1 root root  64 Jul  3 16:58 3 -> /dev/pts/3
lrwx------ 1 root root  64 Jul  3 17:00 4 -> 'socket:[1072739]'
lrwx------ 1 root root  64 Jul  3 17:00 5 -> /run/utmp
lrwx------ 1 root root  64 Jul  3 17:00 6 -> /dev/ptmx

Oh, I also had to use sudo.
So the permission is an issue too.

(03-07-2016, 12:41 PM)vain Wrote: From what I understand, terminal emulators call `openpty()` which gets them a pair of connected file descriptors. The "slave" end is something like `/dev/pts/4` and this is what the shell and other programs see. So, what I'm really looking for would be the "master" end. Meaning, if you run a multiplexer, then that's "the" terminal because this process originally called `openpty()`. (So my script gives the wrong answer, due to missing permissions.)

It's simple to find the slave end because that's STDIN of my script. But how to find the process which holds the corresponding (!) master end? Is that even possible? :/ Even worse: In theory, there could be multiple matching processes because that master file descriptor could be inherited or passed on to other processes (even though that's very unlikely). Traversing the process tree may be a pretty good guess, but it's not necessarily correct.

It also got me thinking into the definition of what is a terminal.

If you write a terminal that works using two parts, client and server, which one do you consider to be the terminal?
Probably the server but there's no direct interaction with the server.

Quote:The role of the terminal emulator process is:

to interact with the user.
to feed text input to the master pseudo-device for use by the shell (such as bash), which is connected to the slave pseudo-device).
To read text output from the master pseudo-device and show it to the user.