Graceful restart and restart
During a normal restart, the server is stopped and then started which means the parent causes it to immediately attempt to kill off all of its children. It may take it several seconds to complete killing off its children. Then the parent itself exits.
for eg.in apache web server
apachectl -k stop/restart
Graceful signal causes the parent process to advise the children to exit after their current request
Then parent re-reads its configuration files and re-opens its log files.When each child dies off the parent replaces it with a new child and serving new requests immediately.
eg. for a graceful restart in apache web server
apachectl -k graceful