How to add user to sudo group in ubuntu server

Question

I tried to add user to sudoers with adduser username sudo, as well as in /etc/sudoers, but it cannot be change because is read only.

Can someone help me please?

Solution

but it cannot be change because is read only.

this is because you don't run the command with sudo and thus as normal user and this is not granted for normal user.

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From another sudo user or root user run the command replacing ussername with your user:

sudo adduser <username> sudo

The change will take effect the next time the user logs in..

Read this community wiki: https://help.ubuntu.com/community/RootSudo#Allowing_other_users_to_run_sudo