How to solve this error `sudo: /usr/local/bin/sudo must be owned by uid 0 and have the setuid bit set` without reinstalling ubuntu?

Question

TLDR: I am running Ubuntu 18.04 with i3 and I messed up my permissions. Whenever I run a command with sudo, I get this error message, sudo: /usr/local/bin/sudo must be owned by uid 0 and have the setuid bit set. I am trying to figure out if I need to fully re-install Ubuntu or if this can be fixed in a less drastic way.

What had happened was: I was trying to upgrade my npm version with nvm and the nvm command was not being recognized. I followed this stackoverflow post's instructions https://stackoverflow.com/questions/21215059/cant-use-nvm-from-root-or-sudo to copy the version of node I had active via nvm into the /usr/local. I ran the below. (Yes, I realize now that I should have investigated this series of commands before running them.)

n=$(which node); \
n=${n%/bin/node}; \
chmod -R 755 $n/bin/*; \
sudo cp -r $n/{bin,lib,share} /usr/local

I then got tons of errors saying chmod: changing permissions of '/usr/bin/*': Operation not permitted

After that I ran sudo nvm install-latest-npm and got the same error as I had before, sudo: nvm: command not found.

Then I tried running another command with sudo, and got the error sudo: /usr/local/bin/sudo must be owned by uid 0 and have the setuid bit set. I now get this error whenever I run anything with sudo.

I think this problem was caused by me running chmod -R 755 $n/bin/*; \ but I'm confused because the error message said permissions for /usr/bin were not changed.
I have a two-part question: 1) What caused this error? Am I correct that it was caused by the chmod -R command? 2) Can I fix this without completely reinstalling ubuntu? If so, how?

For context, I already read these two questions sudo: /usr/lib/sudo/sudoers.so must be owned by uid 0 and this /usr/bin/sudo must be owned by uid 0 and have the setuid bit set. However, I am not sure if the advice from the first question's answer applies to this situation, because the error message I receive is not referring specifically to /usr/lib/sudo/sudoers.so.

Thanks for reading!

Solution

must be owned by uid 0 and have the setuid bit set

1. Check the current owner and permissions with ls -l /usr/bin/sudo. It should similar to:

   -rwsr-xr-x 1 root root 157192 2018-08-23 10:36:40 /usr/bin/sudo

2. Run pkexec bash in a terminal to get a shell with root permissions.

3. Fix ownership of the file:

   chown root:root /usr/bin/sudo
   

4. Set the setuid bit:

   chmod u+s /usr/bin/sudo
   

5. sudo should now be available for you to make further repairs.

Comments

[steeldriver]

Possibly a more relevant previous question is What if I accidentally run command “chmod -R” on system directories (/, /etc, …)

[Terrance]

Possible solution: askubuntu.com/a/634013/231142

[Terrance]

Pretty good thinking! Back when I wrote my answer I didn't even know about pkexec. I sure do now! Great answer!

[ByteByByte]

@xiota Thank you for this very thorough response. When I checked the current owner and permissions, it was extremely similar to what you showed, -rwsr-xr-x 1 root root 149080 Jan 17 2018 /usr/bin/sudo. However, when I ran pkexec bash, I got an error message, pkexec must be setuid root. Since I wasn't able to get a shell with root permissions, I am going to boot up in recovery mode and run the suggested commands from a shell in root mode there. I will let you know if that approach works.

[xiota]

While you are fixing sudo, you probably need to fix pkexec too.

[ByteByByte]

I ran the commands you listed from a root shell in recovery mode. Unfortunately, I still can't use sudo or pkexec outside of recovery mode, and I get the same error messages as I did previously. What should I do to fix pkexec? (I tried googling this but didn't find anything helpful)

[xiota]

probably whatever you did did too much damage, and you'll need to reinstall.

[Paul Jurczak]

Thank you. pkexec bash is so much better than rebooting in maintenance mode!