set environment variable SSH_ASKPASS or askpass in sudoers, resp

Question

I'm trying to login to a ssh server and to execute something like:

ssh [email protected] 'sudo echo "foobar"'

Unfortunately I'm getting an error:

sudo: no tty present and no askpass program specified

Google told me to either set the environment variable SSH_ASKPASS or to set askpass in the sudoers file. My remote machine is running on Debian 6 and I've installed the packages ssh-askpass and ssh-askpass-gnome and my sudoers file looks like this:

Defaults        env_reset
Defaults        askpass=/usr/bin/ssh-askpass

# User privilege specification
root    ALL=(ALL) ALL
user    ALL=(ALL) ALL

Can someone tell what I'm doing wrong and how to do it better.

Answer 1

There are two ways to get rid of this error message. The easy way is to provide a pseudo terminal for the remote sudo process. You can do this with the option -t:

ssh -t [email protected] 'sudo echo "foobar"'

Answer 2

Rather than allocating a TTY, or setting a password that can be seen in the command line, do something like this.

Create a shell file that echo's out your password like:

#!/bin/bash

echo "mypassword"

then copy that to the node you want using scp like this:

scp SudoPass.sh somesystem:~/bin

Then when you ssh do the following:

ssh somesystem "export SUDO_ASKPASS=~/bin/SudoPass.sh;sudo -A command -parameter"

Answer 3

Another way is to run sudo -S in order to "Write the prompt to the standard error and read the password from the standard input instead of using the terminal device" (according to man) together with cat:

cat | ssh [email protected] 'sudo -S echo "foobar"'

Just input the password when being prompted to.

One advantage is that you can redirect the output of the remote command to a file without "[sudo] password for …" in it:

cat | ssh [email protected] 'sudo -S tar c --one-file-system /' > backup.tar

Answer 4

Defaults askpass=/usr/bin/ssh-askpass

ssh-askpass requires X server, so instead of providing a terminal (via -t, as suggested by nosid), you may forward X connection via -X:

ssh -X [email protected] 'sudo echo "foobar"'

However, according to current documentation, askpass is set in sudo.conf as Path, not in sudoers.