xxx is not in the sudoers file.This incident will be reportedの解決方法
エラーメッセージ:
yamada_user is not in the sudoers file. This incident will be reported.
解決方法
#chmod u+w /etc/sudoers
#vi /etc/sudoers
## Allow root to run any commands anywhere
root ALL=(ALL) ALL
追記
yamada_user ALL=(ALL) ALL