i do not want to give our passphrase for a remote login on server machine.for that i start used ssh agent feature.
i just wrote this command on my local machine
$ssh-add
and i got this error message ------------
Could not open a connection to your authentication agent

i also tried with this command-------
ssh-add ~/.ssh/id_dsa

but i got same error message-----------
Could not open a connection to your authentication agent

and ssh-agent program is running on mine local machine because when i execute this command-------
ps aux|grep ssh-agent

and i got this output-----
amitg 1229 0.0 0.0 3368 192 ? Ss 09:56 0:00 /usr/bin/ssh-agent /usr/bin/dbus-launch --exit-with-session gnome-session --session=ubuntu
amitg 2107 0.0 0.0 4160 868 pts/3 S+ 10:24 0:00 grep --color=auto ssh-agent


help me......

If 'env|grep SSH_AGENT_PID' doesn't return anything then you need to export the PID ssh-agent runs as. For example try running 'export SSH_AGENT_PID=$(pgrep ssh-agent) && ssh-add -l || ssh-add;' in your shell.

BTW: easier / efficient would be to run 'pgrep ssh-agent' (or 'ps --no-headers -o pid -C ssh-agent').

still the same error is coming....

What does '/usr/bin/ssh-agent; env|grep SSH' return?

After executing this command---------
/usr/bin/ssh-agent; env|grep SSH

I got this message-------------

SSH_AUTH_SOCK=/tmp/ssh-tWWZUcKy2213/agent.2213; export SSH_AUTH_SOCK;
SSH_AGENT_PID=2214; export SSH_AGENT_PID;
echo Agent pid 2214;

and when i execute ssh-add after above command i got following message

Could not open a connection to your authentication agent.

Because your session is started as '/usr/bin/ssh-agent /usr/bin/dbus-launch --exit-with-session gnome-session --session=ubuntu' all its child processes should see the SSH_AGENT_PID and SSH_AUTH_SOCK variables automagically. Your reply means these did not get exported. Did you make any permission changes to the system? Anyway, running 'eval echo `/usr/bin/ssh-agent -s`; ssh-add' should update your current shell sessions variables and add your key(s).

It should work without the echo command too.