How can I add a new user as sudoer using the command line?

Two ways to use sudo command for a standard user account:

First,

If you want to use sudo command for a standard user account, then you need to add this account to /etc/sudoers file. Use the following steps to add your desired user account to /etc/sudoers file:

• login as administration : i.e.   su – adminuser
• type sudo visudo
• Find out the following

# User privilege specification
root ALL=(ALL) ALL
%admin ALL=(ALL) ALL

• Add your user account below “root ALL=(ALL) ALL”.  For example:

# User privilege specification
root ALL=(ALL) ALL
yourusername ALL=(ALL) ALL
%admin ALL=(ALL) ALL

• Save your file (:wq), and now you will be able to use sudo command for your username.

Second(Recommended),

Just add the user to the sudo group:

sudo adduser <username> sudo

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

This works because /etc/sudoers is pre-configured to grant permissions to all members of this group (You should not have to make any changes to this):

# Allow members of group sudo to execute any command
%sudo   ALL=(ALL:ALL) ALL

As long as you have access to a user that is in the same groups as your "original" user, you can delete the old one.

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Realistically, there are also other groups your new user should be a member of. If you set the Account type of a user to Administrator in Users Settings, it will be placed in at least all of these groups:

adm sudo lpadmin sambashare

Because your system configuration may vary, I suggest taking a look at the output of groups <username> to see what groups are normally in use.