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Test SSH but do not return password prompt

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# 1  
Old 05-01-2012
Test SSH but do not return password prompt
Hello forum,

I want to have a function to test for passwordless SSH setup. Pretty simple. However, what I'm finding difficult is to NOT return a password prompt to screen IF it's not in place.

Here's the function:

Code:
check_passwordless_ssh_working()
#check passed parameter, assuming it is a hostname, to see if SSH works to that host
{
hostname=${1}
passwordless_ssh_whoami=$(ssh -q $hostname whoami)
 
local_whoami=$(whoami)
 
if [[ $passwordless_ssh_whoami = $local_whoami ]] ; then
  passwordless_ssh_working=1
  echo "SSH_working._SSH_response:_$passwordless_ssh_whoami._Local_response:_$local_whoami" $passwordless_ssh_working
else
  passwordless_ssh_working=0
  echo "SSH_NOT_working._SSH_response:_$passwordless_ssh_whoami._Local_response:_$local_whoami" $passwordless_ssh_working
fi
}

It will return the correct string and integer either way, however if the SSH command does not utilise a passwordless (key pair) SSH setup, then it prompts for the target user's password - you have to get it wrong 3 times to make it fail. I want it to just auto-fail here rather than prompting for a password - any idea how I can do this?
# 2  
Old 05-01-2012
There are options to only allow public key auth. Use those options and test for success.

Code:
    if ssh -o BatchMode=yes "$hostname" true 2>/dev/null; then
        echo "it works"
    else
        echo "it's broken."
    if

This User Gave Thanks to neutronscott For This Post:
doonan_79
# 3  
Old 05-01-2012
You can disallow ChallengeResponseAuthentication in ssh_config or ssd_config on the server you should default to key based auth only
This User Gave Thanks to Skrynesaver For This Post:
doonan_79
# 4  
Old 05-08-2012
FOLLOW UP:

FYI Have now tested code and implemented a change following NeutronScott's tip. See working function:

Code:
check_passwordless_ssh_working()
#check passed parameter, assuming it is a hostname, to see if SSH works to that host
{
hostname=${1}
passwordless_ssh_whoami=$(ssh -q -o BatchMode=yes $hostname whoami)
 
local_whoami=$(whoami)
 
if [[ $passwordless_ssh_whoami = $local_whoami ]] ; then
  passwordless_ssh_working=1
  echo "SSH_working._SSH_response:_$passwordless_ssh_whoami._Local_response:_$local_whoami" $passwordless_ssh_working
else
  passwordless_ssh_working=0
  echo "SSH_NOT_working._SSH_response:_$passwordless_ssh_whoami._Local_response:_$local_whoami" $passwordless_ssh_working
fi
}

The simple addition of the BatchMode option (-o) has allowed us to capture the fact that passwordless SSH isn't working, without prompting for a password.

---------- Post updated at 14:20 ---------- Previous update was at 14:18 ----------

NB Notice I return values in a string using echo. As this is a standard return I can then read them as if in an array, using awk to print $1 and $2. $1 showing the text response and $2 showing the numeric response. This is the reason the text all has underscores and no spaces (so it is auto-read as a single field/entry).
This User Gave Thanks to doonan_79 For This Post:
Corona688
# 5  
Old 05-08-2012
You could also use a non-space separator, i.e. -F":" but that makes sense.
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