Unable to use sudo su - command

ubuntu permissions sudo amazon-ec2

9,667

Solution 1

Normal permissions for /etc/ are: rwx r-x r-x root root

Using chmod 741 /etc/ means to set the permissions /etc/ to rwx r-- --x.

Notice the lack of r in the third field. These three fields represent: Owner, group, others. Since the default owner and group is root you just prevented everyone except root from reading files in /etc/. This is a bad thing^tm.

If you get a root prompt then you can revert these changes easily enough, but for that you need:

Either an already open root prompt.
A way to log in as root or any uid 0 account.(You need to manually set this in Ubuntu.)
Right to su or sudo (which you just broke).
Or access to the filesystem from another OS.
Or reinstall the system. (Easiest to do if you just set it up a few minutes ago, but also the least educative way)

For a normal desktop or a server with remote access card (HP ILO, Dells DRAC etc) I would boot into single user mode, provide the root password if needed, and fix the permissions.

Or I would boot from a liveCD (or pendrive) and do the same.

On Amazon this is a bit harder because you have no physical access. However you can start a second instance and mount your old OS disk from there.

Solution 2

pkexec chmod 0440 /etc/sudoers

Then try sudo -s

9,667

pavan tiwari

Updated on September 18, 2022

Comments

pavan tiwari over 1 year
I am new in ubuntu, i am trying to run following command

sudo su -

Bu i am getting following message
```
sudo: unable to open /etc/sudoers: Permission denied
sudo: no valid sudoers sources found, quitting
sudo: unable to initialize policy plugin
```
Previously it was running but when i run following command
```
chmod 741 /etc/
```
It is stop working, i don't have root user password, i am running my machine on Amazon.

Pls suggest me how can i fix this problem.
Admin about 11 years

thanks for replay , but i don't have pkexec, when i used sudo apt-get install policykit-1 command to get it, it is again showing same error message.
ganesh about 11 years

He just did a chmod 741 /etc/ (no r for others). That is the source of the problem, not FS damage,
pavan tiwari about 11 years

command should be like that ls -l /etc/sudoers
pavan tiwari about 11 years

My FS is not damaged -r--r----- 1 root root 584 2009-03-10 20:25 /etc/sudoers
Sepahrad Salour about 11 years

I forgot to write -l option, Thanks.
Sepahrad Salour about 11 years

@Hennes it's not matter. I talk about something else (Hard Link)