Re: [Fab-user] Fabric 2.4.0 problem - Run method is not being finished

[Jeff Forcier]

Hi Mateusz,

The problem with `su` is that it spawns a new interactive shell, expecting a human user to continue interacting with that shell during a single overall SSH session. Tools like Fabric spawn a new session for every new `run()` or similar, as described in this FAQ:

    http://www.fabfile.org/faq.html#my-cd-workon-export-etc-calls-don-t-seem-to-work

Going by my local `man su` it looks like `su` can take a `-c` argument to run its subshell that way (same as directly running the user's login shell with `-c`, which usually means "run this one interpreted string and exit").

So at a basic level you should be able to solve this by replacing:

    dss.run("su", watchers=[...])

    dss.run("whoami")

with:

    dss.run("su -c whoami", watchers=[...])

though you'd necessarily need to have ALL subsequent commands mixing in the `su -c` and `watchers=` bits; possibly a good spot for a subroutine or subclass method.

We've got a `prefix` context manager that works well for commands that can be strung together with `&&`, but we don't yet have an equivalent for this sort of use case. We'll probably get one eventually!

Best,

Jeff

On Fri, Dec 28, 2018 at 5:17 PM Mateusz <address@hidden> wrote:

Hi There,

I'm trying to use fabric library to control subprocesson on linux device. I've prepared a piece of code, which intention is to log as a root user.
I can't use "sudo" method because that is not existing on the system that i want to control. Also logging directly as "root" is impossible. My idea is to log as a "admin" user and then use "su" command to switch to "root" user.

Code:

from fabric import Connection
from invoke import Responder

sudopass = Responder(pattern=r'Password:', response='adminPassword\n')

with Connection('192.168.0.106', user="admin", port=22, connect_kwargs={"password": "admin"}) as dss:
    command = "uname -s"
    print("Response on {} is: {}".format(command, dss.run(command)))
    command = "whoami"
    print("Response on {} is: {}".format(command, dss.run(command)))
    command = "su"
    print("Response on {} is after executing su command: {}".format(command,
                                                                    dss.run(command, pty=True, watchers=[sudopass])))
    command = "whoami"
    print("Response on {} is: {}".format(command, dss.run(command)))
print("Script end")

Output:

Linux
Response on uname -s is: Command exited with status 0.
=== stdout ===
Linux

(no stderr)
dssadmin
Response on whoami is: Command exited with status 0.
=== stdout ===
dssadmin

(no stderr)
Password: 
/home/dssadmin # 

As you can see script got stuck after sending "su" command. Any ideas how to solve that?

I'm using:
Python 3.7
Fabric 2.4.0

Thanks in advance

Mateusz Glowinski

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--

Jeff Forcier
Unix sysadmin; Python engineer
http://bitprophet.org