I am facing the the following issue as i ran some permission on sudo.

"sudo: /usr/bin/sudo must be owned by uid 0 and have the setuid bit set"

I think to resolve this issue, the following steps should work.

Switch to ubuntu recovery mode.
mount -o remount,rw /
mount --all
chown root:root /usr/bin/sudo
chmod 4755 /usr/bin/sudo
restart

My question is how to switch to ubuntu recovery mode?