Sudo: novalidsudoerssourcesfound, quitting

Solve sudo: novalidsudoerssourcesfound. quitting allows common users to use sudochmodu + w/etc/sudoersvi/etc/sudoers to find this line of rootALL (ALL) ALL, and add usernameALL (ALL) under it) ALL but after the return... solve sudo: no valid sudoers sources found. quitting sets sudochmod u + w/etc/sudoersvi/etc/sudoers to find this line of root ALL = (ALL) ALL, the following error occurs when username ALL = (ALL) ALL is added but sudo is returned: sudo: no valid sudoers sources found, the quittin solution is to restore the/etc/sudoers permission to 440, and switch to the common user to execute sudo ifconfig and report the following error: sudo:/etc/sudoers is mode 0640, shoshould be 0440 sudo: no valid sudoers sources found, quitting exits from normal users, and run: chmod u-w/etc/sudoers or chmod 440/etc/sudoers under root.