This error got while installing boltiot package
.
.
.
.
Pls Help
It has been solved
I had another query what should be enter in ssh password. I enter the ubuntu password but it is incorrect.
so I followed this step 
sudo nano /etc/ssh/sshd_config
PermitRootLogin prohibit-password to PermitRootLogin yes
PasswordAuthentication no to PasswordAuthentication yes
But still it is asking for password. What should i put the password
I can see that you are using Ubuntu. May I know to which server you are trying to ssh?
You need to access remote server only if you are using Digital Ocean’s droplet as mentioned in the training.
Since you are accessing ubuntu on your local machine, you do not have to remotely connect to any server.
If you have a Linux or Mac OS X
You are a lucky user and you don’t need to install any software. Most of the Linux based OS/MacOS have in-built terminals. Open a terminal and log in using the command line, with the following command, substituting the IP address of your Droplet for your server IP.
ssh root@your_server_ip and press enter.
And then type your password that you received in email. After this, you are asked to enter your new password twice for confirmation. Keep this password somewhere safe, because next time you have to type this new password.
…
…
In training it is given that login to the server
So I tried according to it but not understanding about the password
You are using VirtualBox on your personal laptop to access Linux instance.
The instructions that you have mentioned are to be followed ONLY if you have created Digital Ocean account and using their droplet to access lLnux instance.
So there is no need of digital ocean??