OCI’s default user is ubuntu. To add a new user and to delete an user, follow the step below.

sudo -i
adduser username
passwd username
cp /home/ubunadu/.ssh /home/username/ -r
chown -R username:username /home/username/.ssh

vi /etc/sudoers

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# User privilege specification
root     ALL=(ALL:ALL) ALL
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# User privilege specification
root     ALL=(ALL:ALL) ALL
username   ALL=(ALL:ALL) ALL
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sudo deluser --remove-home ubuntu