The usual way to run the agent is from the ~/.xsession file:

eval `gpg-agent --daemon`

If you don't use an X server, you can also put this into your regular startup file ~/.profile or .bash_profile. It is best not to run multiple instance of the gpg-agent, so you should make sure that only one is running: gpg-agent uses an environment variable to inform clients about the communication parameters. You can write the content of this environment variable to a file so that you can test for a running agent. This short script may do the job:

if test -f $HOME/.gpg-agent-info &&    kill -0 `cut -d: -f 2 $HOME/.gpg-agent-info` 2>/dev/null; then
     GPG_AGENT_INFO=`cat $HOME/.gpg-agent-info`
     export GPG_AGENT_INFO
else
     eval `gpg-agent --daemon`
     echo $GPG_AGENT_INFO >$HOME/.gpg-agent-info
fi

Note that the new option --write-env-file may be used instead.

You should always add the following lines to your .bashrc or whatever initialization file is used for all shell invocations:

GPG_TTY=`tty`
export GPG_TTY

It is important that this environment variable always reflects the output of the tty command. For W32 systems this option is not required.

Please make sure that a proper pinentry program has been installed under the default filename (which is system dependant) or use the option pinentry-pgm to specify the full name of that program. It is often useful to install a symbolic link from the actual used pinentry (e.g. `/usr/bin/pinentry-gtk') to the expected one (e.g. `/usr/bin/pinentry').