I made a big mistake by running:
sudo chmod -R 777 /
After that, a problem appeared, which is that sudo won't work anymore.
When I run sudo in any command this error appears:
sudo: /usr/bin/sudo must be owned by uid 0 and have the setuid bit set
And when I searched for the problem I figured out that some permissions are messed up
in the /usr/bin/sudo file but I can no longer become root so I can change the permissions!
Seems like re-installing Ubuntu is the easiest way to go from here.
Let's look at the command, bit by bit:
sudo - executes with root permissions (allows for maximum destruction)
chmod - changes the permissions of files (harmless if used correctly)
-R - recursive, descend into directories (could cause trouble)
/ - when combined with -R and sudo, recursively change all the files on your system to global-read-write-execute (very bad)
As you can see, you've basically soft-bricked your system.
Many programs and files on your Linux system require permissions to keep them afloat.
Unless you're willing to spend a lot of your time manually fixing the permissions, re-installing Ubuntu is the way to go.
Backup your data with a live CD, then delete your Linux partitions.
When you install Ubuntu for the second time, create new partitions.
sudo. – You'reAGitForNotUsingGit Aug 07 '16 at 23:46