Ubuntu SSH key and user creation

Create key:

ssh-keygen -t rsa -b 4096 -C "Key description"

and choose the key file name and location.

To login using this key use this command:

ssh username@1.2.3.4 -i /path-to-key-file-no-pub

To add a user in the target system:

adduser username

To add the user to sudoers use:

usermod -aG sudo username

To test:

su - username

and enter a sudo command.

To add the public key in the user home, create this file and paste in it the public key with this commands:

mkdir .ssh
nano .ssh/authorized_keys

and change the file permissions:

chmod 600 .ssh/authorized_keys