Running

Make sure you reduce the stack size before running greylist. Each thread has its own stack so if your default stack size is 8MB (Linux 64 bit) you end up with a memory usage of 800MB with 100 active threads.
A sane size on Linux 64 bit is 64KB

ulimit -s 64

While greylist is running you can send signals to it. On Linux use the kill or killall command.
Supported signals:

SIGQUIT (3)
shutdown
SIGHUP (1)
reload configuration
SIGUSR2 (12)
reload all cached data

Errors and other information are logged to the mail log (LOG_MAIL). For instance, if you signal greylist to reload its configuration and there is an error in the new configuration, greylist will report the error in the mail log and revert to the previous configuration.
During the initial startup errors are reported directly and greylist terminates.

Postfix

Once greylist is running postfix needs to be configured to use it. Edit main.cf and add this:

smtpd_recipient_restrictions =
         reject_unauth_destination
         check_policy_service inet:127.0.0.1:4096

More information is in the Postfix SMTP Access Policy Delegation.

Included with release 2 is a simple Debian style init.d script. Simply copy it to /etc/init./d and enable it with

update-rc.d greylist defaults
/etc/init.d/greylist start