Bash: get output of sudo command on remote using SSH

Question

I'm getting incredibly frustrated here. I simply want to run a sudo command on a remote SSH connection and perform operations on the results I get locally in my script. I've looked around for close to an hour now and not seen anything related to that issue.

When I do:

#!/usr/bin/env bash

OUT=$(ssh username@host "command" 2>&1 )
echo $OUT

Then, I get the expected output in OUT.

Now, when I try to do a sudo command:

#!/usr/bin/env bash

OUT=$(ssh username@host "sudo command" 2>&1 )
echo $OUT

I get "sudo: no tty present and no askpass program specified". Fair enough, I'll use ssh -t.

#!/usr/bin/env bash

OUT=$(ssh -t username@host "sudo command" 2>&1 )
echo $OUT

Then, nothing happens. It hangs, never asking for the sudo password in my terminal. Note that this happens whether I send a sudo command or not, the ssh -t hangs, period.

Alright, let's forget the variable for now and just issue the ssh -t command.

#!/usr/bin/env bash

ssh -t username@host "sudo command" 2>&1

Then, well, it works no problem.

So the issue is that ssh -t inside a variable just doesn't do anything, but I can't figure out why or how to make it work for the life of me. Anyone with a suggestion?

Your question is better suited to Unix & Linux Stack Exchange. This site is for programming related questions. — Cyrus
– Cyrus, Commented Oct 14, 2018 at 17:05
Consider redirection to to capture the output: stackoverflow.com/a/15170225/10470287 — alfunx
– alfunx, Commented Oct 14, 2018 at 17:06
You are capturing the password prompt because you are redirecting stderr to stdout. The variable capture won't finish running because it's waiting for you to type in the password. — tripleee
– tripleee, Commented Oct 14, 2018 at 17:08
As an aside, you should quote the argument in echo "out"; and don't use uppercase for your private variables. — tripleee
– tripleee, Commented Oct 14, 2018 at 17:10
If you want to use sudo in an non-interactive setting, you really ought to configure it to not ask for a password. — William Pursell
– William Pursell, Commented Oct 14, 2018 at 17:30

alfunx · Accepted Answer · 2018-10-14 19:08:16Z

3

If your script is rather concise, you could consider this:

#!/usr/bin/env bash

ssh -t username@host "sudo command" 2>&1 \
    | ( \
        read output
        # do something with $output, e.g.
        echo "$output"
    )

For more information, consider this: https://stackoverflow.com/a/15170225/10470287

answered Oct 14, 2018 at 19:08

alfunx

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2 Comments

William Abma Over a year ago

Hmm, this shows the same issues. On a side note, this only returns the first line (as it encounters a newline). I can't bypass this easily, as read -N is an illegal option on my Mac system. I'll try and see if I can upgrade the bash version.

William Abma Over a year ago

This does make me think that there may be some shenanigans going on with the bash version that's installed on my Mac machine, communicating with a Ubuntu server. I wouldn't know why, but not sure why else I would have issues.

Joe Coder · Accepted Answer · 2024-10-23 06:45:26Z

0

In this situation, you can use tee to reveal the sudo prompt while also capturing the output of the ssh command in a temp file.

tempfile=$(mktemp)
ssh -t username@host "sudo command" | tee $tempfile

Keep in mind that this will also capture the sudo prompt and all stderr output from the remote shell in the output file, because stdout & stderr are both connected to the client shell's stdout when using ssh -t.

edited Oct 23, 2024 at 6:45

answered Oct 23, 2024 at 6:27

Joe Coder

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