Most of the code samples I’ve seen are trying to read from stdin without local echo. To do this they modify the “local modes” flag to remove the setting to “Echo input characters”. I thought I could just modify the “input modes” flag to TIOCSTI
which is for “Insert the given byte in the input queue.”. However, even though I run the script as root, it has no effect. anything I write to the fd seems to go to the terminal output, rather than the terminal input. Basically what I want to do is this exact thing, but in pure python.
""" termfake.py Usage: sudo python termfake.py /dev/ttys002 Get the tty device path of a different local termimal by running `tty` in that terminal. """ import sys import termios fd = open(sys.argv[1], 'w') fdno = fd.fileno() # Returns [iflag, oflag, cflag, lflag, ispeed, ospeed, cc] tatters = termios.tcgetattr(fdno) print('original', tatters) tatters[0] = termios.TIOCSTI print('TIOCSTI', termios.TIOCSTI) # Set iflag termios.tcsetattr(fdno, termios.TCSANOW, tatters) # Verify setting change with open('/dev/ttys002', 'w') as fd2: print('modified', termios.tcgetattr(fd2.fileno())) fd.write('This is testn') fd.close()
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Answer
TIOCSTI
is an ioctl (documented in tty_ioctl(4)), not a terminal setting, so you can’t use tcsetattr()
— you need to feed each character of the fake input to ioctl()
instead. Never had to do ioctl’s from Python before, but the following seems to work for running an ls
in a different terminal (specified as the argument, e.g. /dev/pts/13) that’s running Bash:
import fcntl import sys import termios with open(sys.argv[1], 'w') as fd: for c in "lsn": fcntl.ioctl(fd, termios.TIOCSTI, c)
TIOCSTI
requires root privileges (or CAP_SYS_ADMIN
to be more specific, but that’s usually the same in practice) by the way — see capabilities(7).