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 delegate methods in Rails, exposing only necessary methods of containing objects, thereby, making them more easily accessible. class Parent   def initialize     @child = Child.new   end end class Child   def initialize     @data = []   end   def insert(data)     @data << data   end   def fetch(key)     @data[key]   end end parent = Parent.new if you try this parent.insert("imrahul") then you will get response undefined method `insert' for #<Parent:0x000055f4915673a0 @child=#<Child:0x000055f491567350 @data=[]>> (NoMethodError)   This code will work if we overide methods of child class class Parent   def initialize     @child = Child.new   end   def insert(data)     @child.insert(data)   end   def fetch(index)     @child.fetch(index)   end end class Child   def initialize     @data = []   end   def insert(data)     @data << data   end   def fetch(key)     @data[key]   end end parent = Parent.new parent.insert("imrahul") So this is how dele

sudo apt-get remove elasticsearch sudo apt-get --purge autoremove elasticsearch sudo dpkg --remove elasticsearch sudo dpkg --purge elasticsearch sudo dpkg --purge --force-all elasticsearch sudo rm -rf /var/lib/elasticsearch/ sudo rm -rf /etc/elasticsearch If still facing any issues then you have to delete source file too. cd /etc/apt/sources.list.d/ sudo rm -rf elastic-*   Install Elasticsearch in ubuntu 20, 18, 16

Look for OpenJDK in APT sudo apt search openjdk Install OpenJDK 8 sudo apt-get install openjdk-8-jdk Add the proper GPG key for ElasticSearch wget -qO - https://artifacts.elastic.co/GPG-KEY-elasticsearch | sudo apt-key add - Make sure to install/update transport sudo apt-get install apt-transport-https Save the repo definition echo "deb https://artifacts.elastic.co/packages/5.x/apt stable main" | sudo tee -a /etc/apt/sources.list.d/elastic-5.x.list Update APT and install ElasticSearch from APT sudo apt-get update && sudo apt-get install elasticsearch Reload the daemon sudo /bin/systemctl daemon-reload Allow ElasticSearch to start on boot sudo /bin/systemctl enable elasticsearch.service Lets fire up ElasticSearch... sudo systemctl start elasticsearch.service Lets see if we have some logs sudo ls -la /var/log/elasticsearch/ Have a look at the logs and make sure that ElasticSearch has properly initiated sudo cat /var/log/elasticsearch/elasticsearch.