Permission denied for all sudo comands

1. Mount your Ubuntu installation by clicking on the device's icon in the file manager.

2. Open a terminal and cd into the /usr/bin folder of that installation you mounted from above.

3. Run this command to give all users execute permissions

sudo chmod -R a+x .

4. Run this command to give all users read permissions

sudo chmod -R a+r .

5. Run this command to remove all users (except root's) write permissions

sudo chmod -R o-w .

6. Reboot and see if it works.