HOW TO: Password-less SSH login

Steps to create a password-less SSH login

These commands are executed on linux or on a pseudo-linux environment, like cygwin. It will not work under Windows.

1. Generate the encryption key. Do this on client machine.

   $ ssh-keygen -t dsa -f  ~/.ssh/id_dsa -C "you@client.com"

   A passphrase is recommended, though not required. Enter a passphrase that you can remember. It need not be the same as your password.

2. Skip this step if there are multiple clients connecting to the server.

   $ scp ~/.ssh/id_dsa you@server.com

   Enter the password, when asked.

3. This step is required if there are multiple clients who need to connect to the server.

   $ cat ~/.ssh/id_dsa | ssh you@server.com 'cat - >> ~/.ssh/authorized_keys'

   Now if you try to connect to the server, it won’t ask for your password. If you have setup a passphrase, you are required to enter that.Do the steps below to ensure a password-less login.

4. Edit your bash_profile to include the following lines. This is adapted to cygwin.

   $ cat >> ~/.bash_profile
   SSH_ENV="$HOME/.ssh/environment"
   
   function start_agent {
   echo "Initializing new SSH agent..."
   usr/bin/ssh-agent | sed 's/^echo/#echo/' > "${SSH_ENV}"
   echo succeeded
   chmod 600 "${SSH_ENV}"
   . "${SSH_ENV}" > /dev/null
   /usr/bin/ssh-add;
   }
   # Source SSH settings, if applicable
   if [ -f "${SSH_ENV}" ; then
   . "${SSH_ENV}" > /dev/null
   #ps ${SSH_AGENT_PID} doesn't work under cygwin
   ps -ef | grep ${SSH_AGENT_PID} | grep ssh-agent$ > /dev/null || {
   start_agent;
   }
   else
   start_agent;
   fi

5. For Cygwin, use

   $ cat >> ~/.bash_profile
   if [ -f ${HOME}/.ssh-agent ]; then
   . ${HOME}/.ssh-agent > /dev/null
   fi
   if [ -z "$SSH_AGENT_PID" -o -z "`/usr/bin/ps -a|/usr/bin/egrep \"^[ ]+$SSH_AGENT_PID\"`" ]; then
   /usr/bin/ssh-agent > ${HOME}/.ssh-agent
   . ${HOME}/.ssh-agent > /dev/null
   fi

6. Now type in the last password of this session.

   $ssh-add ~/.ssh/id_dsa

Ok, so we have a password-less login. This is done through the ssh-agent that hods, manages and responds to requests for private keys.

For more information, read An Illustrated Guide to SSH Agent Forwarding
Adapted from – Using ssh-agent with ssh