TL;DR Just Run this command to Kill it
sudo kill -9 $(lsof -i :3000 -t)
Root Cause: Because PID is locked in a file and web server thinks that if that file exists then it means it is already running. Normally when a web server is closed that file is deleted, but in some cases, proper deletion doesn't happen so you have to remove the file manually New Solutions
when you run rails s
=> Booting WEBrick
=> Rails 4.0.4 application starting in development on http://0.0.0.0:3000
=> Run rails server -h
for more startup options
=> Ctrl-C to shutdown server
A server is already running. Check /your_project_path/tmp/pids/server.pid. Exiting
So place your path shown here /your_project_path/tmp/pids/server.pid
and remove this server.pid file:
rm /your_project_path/tmp/pids/server.pid
OR Incase you're server was detached then follow below guidelines:
If you detached you rails server by using command "rails -d" then,
Remove rails detached server by using command
ps -aef | grep rails
OR by this command
sudo lsof -wni tcp:3000
then
kill -9 pID
OR use this command
To find and kill process by port name on which that program is running. For 3000 replace port on which your program is running.
sudo kill -9 $(lsof -i :3000 -t)
Old Solution:
rails s -p 4000 -P tmp/pids/server2.pid
Also you can find this post for more options Rails Update to 3.2.11 breaks running multiple servers