Error when running sudo, getting a permission denied

Question

I was installing GIT on my machine, when I sudo any thing, this error message appears:

sudo: must be setuid root 

I tried from recovery mode to change permissions of usr/bin/sudo by:

chown root:root /usr/bin/sudo
chmod 4755 /usr/bin/sudo
chmod 0440 /etc/sudoers

but the chown or chmod not working cause the file is read only.

Answer 1

When starting in recovery mode your / file system is mounted read-only. So the first command must be

mount / -o remount,rw

after that the commands you found yourself will solve your problem.