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 wa

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-owner 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 + '\n')
stdin.flush()

command = 'whoami'
stdin.write(command + '\n')
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 general SSH/shell question.