Your tomcat-users.xml
looks good.
Make sure you have the manager/
application inside your $CATALINA_BASE/webapps/
You have to install tomcat-admin package: sudo apt-get install tomcat8-admin
(for version 8)
I am using Eclipse. I had to copy the manager/
folder from C:\Program Files\apache-tomcat-8.5.20\webapps
to my Eclipse workspace (~\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\webapps\
).