I tried user is not in the sudoers file and My user is not in the sudoers file with the same result:
root@avilellaM710t:/home/avilella# sudo adduser avilella sudo
The user `avilella' is already a member of `sudo'.
root@avilellaM710t:/home/avilella# exit a
vilella@avilellaM710t:~$ sudo ls
[sudo] password for avilella: avilella is not in the sudoers file.
This incident will be reported.
avilella@avilellaM710t:~$ whoami
avilella
Also, see:
root@avilellaM710t:/home/avilella# cat /etc/sudoers
#
# This file MUST be edited with the 'visudo' command as root.
#
# Please consider adding local content in /etc/sudoers.d/ instead of
# directly modifying this file.
#
# See the man page for details on how to write a sudoers file.
#
Defaults env_reset
Defaults mail_badpass
Defaults secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
# Host alias specification
# User alias specification
# Cmnd alias specification
# User privilege specification
root ALL=(ALL:ALL) ALL
# Members of the admin group may gain root privileges
%admin ALL=(ALL) ALL
# Allow members of group sudo to execute any command
%sudo ALL=(ALL:ALL) ALL
# See sudoers(5) for more information on "#include" directives:
#includedir /etc/sudoers.d
Any ideas?