sudo: >>> /etc/sudoers: syntax error near line 30 <<<
sudo: parse error in /etc/sudoers near line 30
sudo: no valid sudoers sources found, quitting
sudo: unable to initialize policy plugin

mount -o remount,rw /

EDITOR=nano visudo

sudo: >>> /etc/sudoers: syntax error near line 25 <<<
sudo: parse error in /etc/sudoers near line 25
sudo: no valid sudoers sources found, quitting
sudo: unable to initialize policy plugin

pkexec visudo

# /etc/sudoers
#
# This file MUST be edited with the 'visudo' command as root.
#
# See the man page for details on how to write a sudoers file.
#

Defaults    env_reset

# Uncomment to allow members of group sudo to not need a password
# %sudo ALL=NOPASSWD: ALL

# Host alias specification

# User alias specification

# Cmnd alias specification

# User privilege specification
root    ALL=(ALL) ALL

# Members of the admin group may gain root privileges
%admin ALL=(ALL) ALL

EDITOR=gedit visudo

chmod 440 /etc/sudoers

chmod 775 /etc/sudoers.d

chmod 440 /etc/sudoers.d/README