Fix for – W: Failed to fetch Temporary failure resolving ‘’

Problem: apt-get update gives an error :

W: Failed to fetch Temporary failure resolving ''

Reason: Name server is not configured correctly.

Solution : Use Google’s nameservers as below-

echo "nameserver" | sudo tee /etc/resolv.conf > /dev/null


Apt get should work now.


View logs and debug a docker service


To debug why a container within a docker stack didn’t start, these commands will help

#list all processes

docker service ls

#note the id of your problematic service

docker service ps <problematic-service-id-from-above>

#lists all containers of this service. note the id of the most recent container

docker inspect <container-id-from-above-step>

How to install Docker Compose on Ubuntu 18.04 LTS

Here’s how to install docker-compose on Ubuntu LTS :

Open terminal and run these commands

sudo curl -L "$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose

sudo chmod +x /usr/local/bin/docker-compose

Now verify installation

docker-compose --version

This should show the version of docker compose that was installed.

GCloud gives warning : `docker-credential-gcloud` not in system PATH

Problem :

On an Ubuntu VM, the Docker pulls from Gcloud private repository give the error

Error response from daemon: unauthorized: You don't have the needed permissions to perform this operation, and you may have invalid credentials. To authenticate your r
equest, follow the steps in:

After this to reconfigure auth, the following command is issued :

gcloud auth configure-docker

This gives the error:

WARNING: `docker-credential-gcloud` not in system PATH.
gcloud's Docker credential helper can be configured but it will not work until this is corrected.
gcloud credential helpers already registered correctly.


Issue these commands on terminal

sudo su

curl -fsSL "" | tar xz --to-stdout ./docker-credential-gcr > /usr/bin/docker-credential-gcr && chmod +x /usr/bin/docker-credential-gcr

docker-credential-gcr configure-docker

docker pull <your-image>

The docker pulls should work now.


Spring boot and Hibernate Second Level cache giving NoCacheRegionFactoryAvailableException


Setting below in,


Gives the error:

org.hibernate.cache.NoCacheRegionFactoryAvailableException: Second-level cache is used in the
application, but property hibernate.cache.region.factory_class is not given, please either
disable second level cache or set correct region factory class name to property
hibernate.cache.region.factory_class (and make sure the second level cache provider,
hibernate-infinispan, for example, is available in the classpath).


Move the above settings from to


Openfire with Smack disconnects with error : You acknowledged stanzas that we didn’t send


Problem: After connecting, openfire servers disconnects from Smack client giving an exception as below –

Connection XMPPTCPConnection[] (0) closed w
ith error

org.jivesoftware.smack.XMPPException$StreamErrorException: undefined-condition You can read more about the meaning of this stream error at
<stream:error><undefined-condition xmlns='urn:ietf:params:xml:ns:xmpp-streams'/><text>You acknowledged stanzas that we didn&apos;t send. Your Ack h: 11, our last stanz
a: 10</text></stream:error>
 at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader.parsePackets( [smack-tcp-4.3.0.jar:4.3.0]



  1. In Openfire admin too, go to Server Manager => Server Properties
  2. Set = false


Fix : /boot disk has no space ( on Ubuntu)

Problem : /boot disk has no space, thus blocking installation or removal of any package using apt-get

Fix :

In terminal –

cd /boot


sudo rm -r abi-4.4.0-89-generic abi-4.4.0-92-generic config-4.4.0-89-generic config-4.4.0-92-generic initrd.img-4.4.0-89-generic initrd.img-4.4.0-92-generic vmlinuz-4.4.0-89-generic vmlinuz-4.4.0-92-generic

(From the listed files, remove least two versions of every file)


This command searches of kernel files not in use and removes them to make space.