Run interactive Bash with popen and a dedicated TTY Python

Question

I need to run an interactive Bash instance in a separated process in Python with it's own dedicated TTY (I can't use pexpect). I used this code snippet I commonly see used in similar programs:

master, slave = pty.openpty()  p = subprocess.Popen(["/bin/bash", "-i"], stdin=slave, stdout=slave, stderr=slave)  os.close(slave)  x = os.read(master, 1026)  print x  subprocess.Popen.kill(p) os.close(master) 

But when I run it I get the following output:

$ ./pty_try.py bash: cannot set terminal process group (10790): Inappropriate ioctl for device bash: no job control in this shell 

Strace of the run shows some errors:

... readlink("/usr/bin/python2.7", 0x7ffc8db02510, 4096) = -1 EINVAL (Invalid argument) ... ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 0x7ffc8db03590) = -1 ENOTTY (Inappropriate ioctl for device) ... readlink("./pty_try.py", 0x7ffc8db00610, 4096) = -1 EINVAL (Invalid argument) 

The code snippet seems pretty straightforward, is Bash not getting something it needs? what could be the problem here?

Answer 1

This is a solution to run an interactive command in subprocess. It uses pseudo-terminal to make stdout non-blocking(also some command needs a tty device, eg. bash). it uses select to handle input and ouput to the subprocess.

#!/usr/bin/env python # -*- coding: utf-8 -*-  import os import sys import select import termios import tty import pty from subprocess import Popen  command = 'bash' # command = 'docker run -it --rm centos /bin/bash'.split()  # save original tty setting then set it to raw mode old_tty = termios.tcgetattr(sys.stdin) tty.setraw(sys.stdin.fileno())  # open pseudo-terminal to interact with subprocess master_fd, slave_fd = pty.openpty()   try:     # use os.setsid() make it run in a new process group, or bash job control will not be enabled     p = Popen(command,               preexec_fn=os.setsid,               stdin=slave_fd,               stdout=slave_fd,               stderr=slave_fd,               universal_newlines=True)      while p.poll() is None:         r, w, e = select.select([sys.stdin, master_fd], [], [])         if sys.stdin in r:             d = os.read(sys.stdin.fileno(), 10240)             os.write(master_fd, d)         elif master_fd in r:             o = os.read(master_fd, 10240)             if o:                 os.write(sys.stdout.fileno(), o) finally:     # restore tty settings back     termios.tcsetattr(sys.stdin, termios.TCSADRAIN, old_tty)