Question about usage with su/interactive session debugging

[isamu-isozaki]

Hi! Thanks a lot for the library.
I was planning to use this library on some virtual boxes I have locally. What I tried to do was login as a low privilege user than login to root like so

import asyncio
import asyncssh
import sys
import time

async def run_client() -> None:
    async with asyncssh.connect('192.168.50.11', username='lowpriv', password='trustno1') as conn:
        try:
            result = await conn.run('echo "Hello!"', check=True)
        except asyncssh.ProcessError as exc:
            print(exc.stderr, end='')
            print(f'Process exited with status {exc.exit_status}',
                file=sys.stderr)
        else:
            print(result.stdout, end='')
        try:
            async with conn.create_process('su root') as process:
                print("Started process")
                time.sleep(1)
                # Send the password to `su` via stdin
                process.stdin.write('aim8Du7h' + '\n')  # Send password

                # Read the output of the `su` command
                result = await process.stdout.read()
                print(f"su root result: {result.decode()}")  # Decode and print output
            print("Ended")
        except asyncssh.ProcessError as exc:
            print(f"Error running su command: {exc.stderr}", file=sys.stderr)

# If you're in an environment where an event loop is already running (like Jupyter or IPython),
# you can simply use 'await' instead of 'run_until_complete'
try:
    # In Jupyter, use 'await' directly to run the coroutine
    asyncio.get_event_loop().run_until_complete(run_client())
except (OSError, asyncssh.Error) as exc:
    sys.exit('SSH connection failed: ' + str(exc))

but my code hangs in started process. My question is more what's a good way to debug this since I'm currently a bit stuck. And again thanks for the library and def feel free to close if there's a better place for questions like this!

[ronf]

I think your problem here might be the use of read() with no argument. That will block waiting for the remote system to return EOF, which won't happen on an interactive shell if you haven't closed stdin. If you pass in a maximum read size, it will return as soon as any data is sent (up to the max bytes you requested).

In terms of debugging, I see you are already adding in print statements. You can add more to narrow down exactly which call it is blocking on, and then start to dig into why. You can also turn on AsyncSSH debugging to see the actual messages being sent and received on the network. Enabling that would look something like:

import logging
logging.basicConfig(level='DEBUG')
asyncssh.set_debug_level(2)

Debug level can be 1 (minimal logging) to 3 (verbose logging with raw packet dumps). In most cases, level 2 is enough.

[isamu-isozaki]

@ronf Wow thank you so much! I noticed that for the output for the password, it was getting sent to stderr instead interestingly but otherwise worked perfectly once I added 999 in read!