Where are Docker images stored on the host machine?

The contents of the /var/lib/docker directory vary depending on the driver Docker is using for storage.

By default this will be aufs but can fall back to overlay, overlay2, btrfs, devicemapper or zfs depending on your kernel support. In most places this will be aufs but the RedHats went with devicemapper.

You can manually set the storage driver with the -s or --storage-driver= option to the Docker daemon.

• /var/lib/docker/{driver-name} will contain the driver specific storage for contents of the images.
• /var/lib/docker/graph/<id> now only contains metadata about the image, in the json and layersize files.

In the case of aufs:

• /var/lib/docker/aufs/diff/<id> has the file contents of the images.
• /var/lib/docker/repositories-aufs is a JSON file containing local image information. This can be viewed with the command docker images.

In the case of devicemapper:

• /var/lib/docker/devicemapper/devicemapper/data stores the images
• /var/lib/docker/devicemapper/devicemapper/metadata the metadata
• Note these files are thin provisioned "sparse" files so aren't as big as they seem.  

 

This answer from stack-overflow.

 

 

Happy learning :) 

What is Docker, learn with simple slides

Docker is a set of platform as a service products that use OS-level virtualization to deliver software in packages called containers. Containers are isolated from one another and bundle their own software, libraries and configuration files; they can communicate with each other through well-defined channels.

Enjoy the slide Please let me know if you have any query.

Java Interview Question

What is transient variable?

Transient variable can't be serialize. For example if a variable is declared as transient in a Serializable class and the class is written to an ObjectStream, the value of the variable can't be written to the stream instead when the class is retrieved from the ObjectStream the value of the variable becomes null.

What do you understand by Synchronization?

Synchronization is a process of controlling the access of shared resources by the multiple threads in such a manner that only one thread can access one resource at a time. In non synchronized multithreaded application, it is possible for one thread to modify a shared object while another thread is in the process of using or updating the object's value. Synchronization prevents such type of data corruption.
E.g. Synchronizing a function:

public synchronized void Method1 () {
// Appropriate method-related code. 
}
E.g. Synchronizing a block of code inside a function:
public myFunction (){
synchronized (this) { 
// Synchronized code here.
}
}

What is Collection API?

The Collection API is a set of classes and interfaces that support operation on collections of objects. These classes and interfaces are more flexible, more powerful, and more regular than the vectors, arrays, and hashtables if effectively replaces. 
Example of classes: HashSet, HashMap, ArrayList, LinkedList, TreeSet and TreeMap.
Example of interfaces: Collection, Set, List and Map.

Explain the Encapsulation principle.

Encapsulation is a process of binding or wrapping the data and the codes that operates on the data into a single entity. This keeps the data safe from outside interface and misuse. One way to think about encapsulation is as a protective wrapper that prevents code and data from being arbitrarily accessed by other code defined outside the wrapper. 

Explain the different forms of Polymorphism.
From a practical programming viewpoint, polymorphism exists in three distinct forms in Java: 

• Method overloading 
• Method overriding through inheritance 
• Method overriding through the Java interface 

 

 

 

Happy Learning .. Wait for more I will added soon..... :)