linux - Executing command using "su -l" in SSH using Python

Question

I use a friends server that allows only one user to be logged from SSH, so normally I just log in as that user and then do su -l myuser to change accounts. I wanted to automate some boring stuff using Python, but I ran into problems with that. Apparently Paramiko module that I tried first invokes a single shell for every command, so that was out of the question. Later I tried using invoke_shell() to overcome that, but it still failed (I assume it's because changing user changes shell as well).

After that I found about Fabric module, but best I could do is open SSH shell with a proper user logged in, but without option to run any commands from code.

Is there any way to accomplish that? Final goal would probably look something like this:

ssh.login(temp_user, pass)
ssh.command("su -l myuser")
expect("Password: ", ssh.send("mypass
")
ssh.command("somescript.sh > datadump.txt")

Using sudo is impossible, as well as adding passwordless login.

As suggested here is the code that I tried with Paramiko:

import paramiko

host = "hostip"
user = "user"
user_to_log = "myuser"
password = "pass"
password_to_log = "mypass"

login_command = "su -l " + user_to_log

ssh = paramiko.SSHClient()
ssh.load_system_host_keys()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect(hostip, username=user, 
    password=password)    

transport = ssh.get_transport()
session = transport.open_session()
session.set_combine_stderr(True)
session.get_pty()


session.exec_command("su -l " + user_to_log)
stdin = session.makefile('wb', -1)


stdin.write(password_to_log +'
')
stdin.flush()

session.exec_command("whoami")
stdout = session.makefile('rb', -1)

for line in stdout.read().splitlines():        
    print('host: %s: %s' % (host, line))

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su -c command won't work either, since server system doesn't support that option.

Answer 1

General disclaimers first (to others who stumble upon this question):

• Using su is not the right solution. su is a tool intended for an interactive use, not for an automation. The correct solution is to login with the correct account directly.

  Or at at least use a password-less sudo.

  Or you can create a root-owned script with setuid right.

  See also Allowing automatic command execution as root on Linux using SSH.

• If you are stuck with su, on most systems you can use -c switch to su to specify a command:

    su -c "whoami" user
  

  See also How to run sudo with Paramiko? (Python)

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If none of the above is feasible (and you really tried hard to make the admin enable some of the options above):

As the last resort option, you can write the command to a standard input of the su, the same way you already write a password (another thing not to do):

stdin, stdout, stderr = session.exec_command("su -l " + user_to_log)

stdin.write(password_to_log + '
')
stdin.flush()

command = 'whoami'
stdin.write(command + '
')
stdin.flush()

(also note that it's redundant to call makefile, as exec_command already returns that)

See Execute (sub)commands in secondary shell/command on SSH server in Python Paramiko.

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Note that your question is not about which SSH client library to use. It does not matter if you use Paramiko or other. This all is actually a generic SSH/Linux/shell question.