ssh_key

Using ssh With Out Passwords

Notation

Variable	Description
machine_local	Name of the machine where you will initiate ssh commands from.
password_local	Your ssh password on machine_local .
comment	A very short comment used to identify the ssh key pair used on machine_local .
type	The type of key pair that machine_local will use. This should be either rsa or dsa .
pid	The process id corresponding to the ssh-agent running on machine_local .
machine_remote	Name of the remote machine where ssh commands will be executed.
usr_remote	Your user name on machine_remote .
password_remote	Your login password on machine_remote .

Step 1: Create Key Pair

On machine_local execute the commands

      cd

      ssh-keygen -t type -C comment

In response to the prompt

Enter file in which to save the key (… . ssh/id_ type ):

hit return (to choose . ssh/id_ type for you private key file). In response to the prompt

Enter passphrase (empty for no passphrase):

enter password_local . In response to the prompt

Enter same passphrase again:

enter password_local .

Step 2: Setup ssh-agent

The following bash script is a modification of a post on a cygwin mailing list:

#
# file where start_ssh_agent store environment variable values
SSH_ENV=${HOME}/.ssh/environment
#
# start a new ssh-agent
function start_ssh_agent {
ssh-agent | sed > ${SSH_ENV} \
-e 's/^echo /# &/'
chmod 600 ${SSH_ENV}
. ${SSH_ENV} > /dev/null
echo "New ssh-agent pid = ${SSH_AGENT_PID}."
}
# check if environment variable is set
if [ "${SSH_AGENT_PID}" == "" ]
then
# check if file with environment variables exists
if [ -f "${SSH_ENV}" ]
then
. ${SSH_ENV} > /dev/null
else
start_ssh_agent;
fi
fi
# make sure environment variable matches process id
if ! ps -ef | grep ${SSH_AGENT_PID} | grep 'ssh-agent' > /dev/null
then
start_ssh_agent;
fi
#
# get the fingerprint for the private key in .ssh
if [ -e .ssh/id_dsa ]
then
id=`ssh-keygen -lf .ssh/id_dsa | sed -e 's/[^ ]* \([^ ]*\).*/\1/'`
fi
if [ -e .ssh/id_rsa ]
then
id=`ssh-keygen -lf .ssh/id_rsa | sed -e 's/[^ ]* \([^ ]*\).*/\1/'`
fi
#
# make sure identity has been added to ssh-agent
if ! ssh-add -l | grep "$id" > /dev/null
then
echo "Run ssh-add to add your identity to ssh-agent."
fi

This script makes sure that the ssh-agent daemon is running. It also prompts you to run ssh-add if you have not already done so. Add this script to the shell initialization file $HOME/.bashrc so that it is run whenever you start a new shell.

You can check if this script is being run by first running

ssh-add -D

to remove all the identities from ssh-agent . Then when you start a new shell, you should see the message

Run ssh-add to add your identity to the agent.

If this script is not run automatically when a shell starts up, you can run it with the command

source $HOME/.bashrc

Step 3: Store Password in ssh-agent

If the script above prints the text

Run ssh-add to add your identity to the agent.

you should to run ssh-add to store a copy of your ssh password in the current ssh-agent . This is done by executing the command

ssh-add

In response to the prompt

Enter passphrase for … . ssh/id_ type :

enter password_local .

Step 4: Copy Public Key

On machine_local execute the command

scp .ssh/id_ type . pub user_remote @ machine_remote :

In response to the prompt

user_remote @ machine_remote ‘ s password:

enter password_remote .

Step 5: Authorization

On machine_local execute the commands

ssh user_remote @ machine_remote

In response to the prompt

user_remote @ machine_remote ‘ s password:

enter password_remote . After the login response, enter the commands

      cat id_ type . pub >> .ssh/authorized_keys

      exit

Step 6: Test Authorization

On machine_local re-execute the command

scp .ssh/id_ type . pub user_remote @ machine_remote :

This time you should not need a password to complete this command. If scp responds

Enter passphrase for key ‘… . ssh/id_ type ‘:

run the script in Step 2 by executing the command

source $HOME/.bash_profile

then run ssh-add , as described in Step 3 , and then try the scp command again.