sudo: unable to stat /etc/sudoers: Permission denied … Mint 18.2 Cinnamon

Question

I messed up some permission issues by trying to change permissions on what I thought was just one directory but what turned out to be '/'. Now I am having sudo problems: In the console as a non-root user, when I try to login as root, I get:

sudo su
sudo: unable to stat /etc/sudoers: Permission denied
sudo: no valid sudoers sources found, quitting
sudo: unable to initialize policy plugin

However I can get root terminal access to a directory by using the GUI Nemo file browser then right clicking and clicking 'open as root'. Most of the other posts with similar issues have had this issue be due to having incorrect file/directory permissions but I don't think this is the exact problem because when I do ls -ld /etc/ / ls -l /etc/sudoers I get:

drwxr-xr-x 157 root root 12288 Dec 15 15:36 /etc/
-rw-r--r-- 1 root root 755 Dec 15 15:36 /etc/sudoers

The update system also seems to not work.

I have tried:

apt-get -o Dpkg::Options::="--force-confmiss" install --reinstall sudo

but this does not seem to really do anything productive

This is the contents of 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:/snap/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

Answer 1

It is not a problem of the sudoers configuration file. You can check the configuration of your file using visudo -c. If you run against your file, you will check that it is parsed OK. I can't identify the problem with only the info you provided, but here are some things you can try.

• Make sure that all the path /etc/sudoers is executable
• Make sure that the / directory is with permissions 755(drwxr-xr-x)
• Try to reconfigure the package with the default values running dpkg-reconfigure as root

Please provide info about the new permissions on /.

PS: I find weird is that your sudoers file has write permissions, remember you should only edit the sudoers file with visudo.