How to fix sudo after “chmod -R 777 /usr/bin”?

Today, by mistakenly, I set the 'sudo chmod -R 777' to my /usr/bin folder as a root user. After doing that, I found that , my sudo command was not working at all. After spending a couple (of) hours over google, finally I got the solution and here I am going to share with you.

In an attempt to set permissions for my local scripts(because as I told you ,I broke the sudo permission and changed ownership, by mistake ), and back the ownership of sudo to root , I followed the following steps:

Step 1: Switch to ubuntu recovery mode. If you are unaware of the process, you can refer an answer here: https://brajeshnotes.blogspot.com/2018/10/how-can-i-start-ubuntu-in-safe-mode.html

Step 2: Once in recovery mode, select root - Drop to root shell prompt

Step 3: Do the following commands.

mount -o remount,rw /
chown root:root /usr/bin/sudo
chmod 4755 /usr/bin/sudo
reboot

Note*: If after reboot , sudo comes up with the same three errors mention below :  

sudo: error in /etc/sudo.conf, line 0 while loading plugin 'sudoers_policy'
sudo: /usr/lib/sudo/sudoers.so must only be writable by owner
sudo: fatal error, unable to load plugins.

Try this :

$ mount -o remount,rw /
$ chmod 644 /usr/lib/sudo/sudoers.so
reboot

Wait for your system to boot normally and you will see the ownership of sudo back to root.After doing these all steps, still you guys facing any problem, please leave your valuable comments here, I will try to answer my best.