Ytdyklly

Always use visudo to edit your sudoers file, never edit it directly yourself. It will prevent you saving it to disk unless it validates.

Type in:

pkexec visudo

Then change last line

#includedir /etc/sudoers

To:

#includedir /etc/sudoers.d

It should solve your problem.

if anyone else like me didn't have pkexec installed, or was not able to run vi, visudo, nano or any other editor to change sudoers file you can be sure with this process.. I was saved with this:

• reboot


• hold shift key while booting to have option for recovery mode (enter it)


• enter command line as root (second last option at my grub menu)


• 
  

  remount boot device for rw, and apply exec right for user, and edit file

  
  
  

  mount -n -o remount,rw /
  
  chmod u+x /etc/sudoers
  
  nano /etc/sudoers
  
  

  
  

fix that mistake and be happy :)

If you messed up your sudoers file, you'll need to:

• Reboot into recovery mode (hit escape during boot, choose the recovery mode option on the grub screen)


• Choose the 'Enable networking' option (if you don't your filesystem will be mounted as read-only. who knew)


• Chosee the 'Drop to root shell' option


• run visudo, fix your file


• Reboot with normal grub option

source :- http://mario.net.au/content/recover-etcsudoers-ubuntu-1204

There is nothing wrong #include sudoer.d
removing #include sudoer.d won't make any difference.

But please make sure you don't have any syntax errors.
I had same issue but and spent hours to fix and just figured out they are syntax errors.
Refer to manual and make them right.

For example
Say your username is : dolly
I used following which is wrong

 dolly ALL = (ALL) ALL NO PASSWD: ALL

correct syntax is

dolly ALL = (ALL) ALL //give permission to everything, not good

or

dolly ALL=(ALL) NOPASSWD:/usr/bin/thurderbird //good, give specific permission

hope this helps

run recovery mode then type this

chown -R root:root /etc/sudoers.d

chmod u=rwx,g=rx,o=rx /etc/sudoers.d/

chmod u=r,g=r,o= /etc/sudoers.d/*

only the group and user root should have read privelege

You can also login as root on a tty console with Ctrl+Fn (Fn from 1 to 6) and run visudo.

You can edit your boot entry while in grub as well.

Simply reboot your pc, and wait for grub to show. Then press "e" on the "Ubuntu" entry to edit it.

Look for a line with "linux = " or "kernel = " and simply add an "single" to the end of that line.

Then press F10 to boot this temporarily modified boot entry.
This will give you a shell (without GUI) with root rights and you can edit the sudoers file with s.th. like nano /etc/sudoers back to its previous state.

Then reboot and its done.

pkexec visudo

then revert your mistakes

In Ubuntu 16.04 running on a VirtualBox (shouldn't make a difference), the above methods didn't work for me (invalid row in the end of the file). What did work was:

1. Restart the VirtualBox


2. Let it boot normally, until it asks for your username & password in the console


3. Login normally with your username


4. Then when you end up in the console (provided your box doesn't boot into a GUI), simply give the command su - and then give your own username's password.


5. It should now end up in root@ubuntu-xenial:~# prompt, if the /etc/sudoers isn't too broken or empty. Not sure what would happen in that case.


6. Then you can simply run visudo and fix the file.


7. Then Ctrl + X and it will prompt to Save modified buffer. Press Y and Enter
   


8. Restart the box and it should work now.

In case your /etc/sudoers is empty or missing something, and you can edit it, then here's the contents of mine:

Defaults env_reset

Defaults mail_badpass

Defaults secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin"



root ALL=(ALL:ALL) ALL



%admin ALL=(ALL) ALL



%sudo ALL=(ALL:ALL) ALL