Possible to pipe command using su via ssh

Question

I'm trying to write a python script to remotely update the login passwords for a set of account I administer - I can already successfully use python to pipe remote commands via the stdin of an ssh process. However, I want to test whether the remote password is correctly set. I can do this I can do this remotely follows:

[localhost]% ssh -t -o RequestTTY=true user@host [host]% su user -c true 

and provide the password at the prompt. This works, but if I try the following remotely:

 [localhost]% echo "su user -c true" | ssh -t -o RequestTTY=true user@host 

I get:

su: must be run from a terminal 

Note, this is not failing because su needed a password (which I'll eventually provide via python) - it fails before then. su doesn't like to be run through a pipe in this way.

What's going on, and how can I pipe input to a remote su command? (or remotely test whether a password is correct for some user).

Answer 1

Pipe the password into the su, which in turn is piped to ssh.

Example below. Note how foopass is the correct password for user foo, so it runs the id command happily. Note how badpass is the wrong password for user foo, so it generates Authentication failure.

$ echo "echo foopass | su foo -c id" | ssh -t -o RequestTTY=yes steve@localhost Pseudo-terminal will not be allocated because stdin is not a terminal. Password: uid=1001(foo) gid=1003(foo) groups=1003(foo) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 $ echo "echo badpass | su foo -c id" | ssh -t -o RequestTTY=yes steve@localhost Pseudo-terminal will not be allocated because stdin is not a terminal. Password: su: Authentication failure $