If you are running devstack environment, you can do restart as below

1. screen -r
2. Move to "q-svc" screen. You can move with Ctrl + a + n (for next), Ctrl+a+p (for previous screen) or you can move to specific screen using number ex: Ctrl+a+7
3. Press Ctrl + c to kill the screen
4. Press up arrow and Press "Enter" key

Things have changed. If you are still working with devstack and you are on ubuntu then it is:

sudo systemctl restart devstack@q-svc.service

Protip: systemctl has tab completion after you identify the service to restart. So, sudo systemctl restart devstack@ and tab complete from there.

service neutron-dhcp-agent restart
service neutron-ovs-cleanup restart
service neutron-metadata-agentrestart
service neutron-l3-agent restart
service neutron-plugin-openvswitch-agent restart
service neutron-vpn-agent restart
service neutron-server  restart

let me tell complete steps:

(Note:Use vncserver or Xmanager)

• First cd to folder devstack

• You can find the file ./rejoin_stack.sh

• Execute the same.

• It will be executed and screen will be opened for access.

• press ctrl + a + shift + "

• Then it will be listing the running services

• can move to service which needs to be stopped by scrolling towards it.

• on the service which is needs to be stopped press enter

• then press ctrl + c , it will stop the service

• then press up arrow key to run the service again

• service will be restarted successfully.