Sudo permissions mixed up

Question

I was messing with ubuntu trying to make autogen.sh work and did a dumb thing. I typed:

sudo chown -R emilia /usr/bin/

and after that I cannot use sudo anymore.

I tried so far:

logging as root and typing:

chown root:root /usr/bin/sudo && chmod 4755 /usr/bin/sudo

Didn't help.

I ran some tests and here are the results:

emilia@emilia:~$ ls -la /usr/bin | grep -v "root *root"
total 147656
drwxr-xr-x  2 emilia root      65536 Aug 14 16:06 .
-rwxr-xr-x  1 emilia root      51920 Feb 18 14:37 [
lrwxrwxrwx  1 emilia root          8 Aug  7 16:04 2to3 -> 2to3-2.7
-rwxr-xr-x  1 emilia root         96 Jul  2 21:02 2to3-2.7

emilia@tenshi:~$ ls -la /usr/bin | grep -v "rwxr-xr-x\|^l"
total 147656
-rwxrwxr-x  1 emilia emilia       22 Aug 14 16:06 autogen.sh

emilia@emilia:~$ ls -l /usr/bin/sudo
-rwxr-xr-x 1 emilia root 136808 Maj  4 19:25 /usr/bin/sudo

Answer 1

Since you cannot use sudo anymore, there are two things you can do:

1. If you have placed a root password (not your user password), use su on a terminal and you will be able to use the root account by using that password.

2. If you haven't placed a root password, you can reboot your system and go to Recovery mode, and open a root session. Since you haven't placed a root password you won't be asked to enter one. After that, type: mount -o rw,remount / and press Enter to enable read/write access to your system.

Having gained root access by either of the methods above, issue chown -R root:root /usr/bin and you should be back to business.

Answer 2

Your commands are not working because recovery mode mounts the file system as read-only. To make it writable, run this command:

mount -o rw,remount /

Now, execute:

chmod 4755 /usr/bin/sudo
chown -R root:root /usr/bin

to fix the permissions.