ramsudharsan is quite right ...
In my case Ubuntu 20.04
Step 1: Switch to ubuntu recovery mode. If you are unaware of the process, you can refer an answer here: https://askubuntu.com/a/172346/223901
My machine → reboot and [Esc] after splash screen. A little tricky, but after a few attemps GRUB show up ...
Step 2: Once in recovery mode, select root - Drop to root shell prompt
Step 3: Do the following commands
# mount -o remount,rw / → on my machine works without!
chown root:root /usr/bin/sudo
chmod 4755 /usr/bin/sudo
reboot
Step 4: After normal reboot/system start
sudo chmod 4755 /usr/bin/[files from the list below]
also the other files (no complet list):
/usr/bin:
- -rwsr-xr-x 1 root root 84K Jul 15 2021 chfn*
- -rwsr-xr-x 1 root root 52K Jul 15 2021 chsh*
- -rwsr-xr-x 1 root root 39K Mär 7 2020 fusermount*
- -rwsr-xr-x 1 root root 87K Jul 15 2021 gpasswd*
- -rwsr-xr-x 1 root root 310K Okt 11 2019 info*
- -rwsr-xr-x 1 root root 55K Jul 21 2020 mount*
- -rwsr-xr-x 1 root root 44K Jul 15 2021 newgrp*
- -rwsr-xr-x 1 root root 67K Jul 15 2021 passwd*
- -rwsr-xr-x 1 root root 31K Mai 26 2021 pkexec*
- -rwsr-xr-x 1 root root 67K Jul 21 2020 su*
- -rwsr-xr-x 1 root root 163K Jan 19 2021 sudo*
- -rwsr-xr-x 1 root root 39K Jul 21 2020 umount*
- -rwsr-xr-x 1 root root 26K Jan 11 2021 xdg-open*
- -rwsr-xr-x 1 root root 30 Nov 12 2017 xlinks2*
/usr/sbin/:
-rwsr-xr-x 1 root dip 386K Jul 23 2020 pppd
/usr/lib/policykit-1/:
-rwsr-xr-x 1 root root 23K Mai 26 2021 polkit-agent-helper-1
Thanks to the recovery mode, there is no need for a reinstallation! ...
pkexec
method in my answer (which you've marked as accepted) solve this problem for you? I've become convinced that, as Damien Roche and Oli have commented, this method does not actually work after asudo chmod -R 777 /usr/bin
command has successfully completed. Likesudo
,pkexec
has to be setuid root to work. (I'm not sure why, as it uses the polkit service, but it does.) However, I think I've heard other people say this has worked for them, which is curious! Had you pressed Ctrl+C before the777
chmod command finished?sudo chmod -R 777 /usr/bin
, but only after logging into theroot
account.