Ubuntu – Why don’t I have a password for “su”? Problems with “sudo”

chmodsudo

I have installed Ubuntu using the GUI, giving myself a password and everything. I do not intricately remember the process. However, what worries me is that I don't know the following password:

$ su
Password: <the only password I've ever created on this machine>
su: Authentication failure

I just don't know what to do. I'm not in trouble, but I just want to know what's going on here. I can also lock myself out of directories:

starkers@ubuntu:~/Desktop$ mkdir foobs
starkers@ubuntu:~/Desktop$ sudo chmod 777 -R foobs
sudo: /var/lib/sudo writable by non-owner (040777), should be mode 0700
[sudo] password for starkers: <the only password I've ever created on this machine> 
starkers@ubuntu:~/Desktop$ cd foobs
bash: cd: foobs: Permission denied

I'm just a bit confused. How can I lock myself out like this? I think sudo is the key command here. But I'm making the foobs file as open as it can possibly be via the chmod, so why does it lock me out?

Best Answer

By default, the superuser (root) account is disabled and doesn't have any password. You can create one by running:

$ sudo passwd root

You will then be able to login as root by running su using this password.

As for chmod, the correct command would be:

$ chmod 777 -R foobs

You can also use:

$ sudo -i

to login as root using your password (without creating a root password as described above).

Related Solutions

Ubuntu – Why does sudo not add root’s PATH with Ubuntu 12.04

Besides security reasons (as Anders has referred to), keeping the original user's PATH also conforms to the Principle of Least Astonishment.

Suppose you run a program called foo, but discover that you really need to run it as root. So you run sudo foo. It would be bad if the program run by sudo foo is different from the program run by foo, which would happen if there's a different foo in root's PATH. This would fundamentally violate your expectations and the general assumption that sudo does the same thing as what you put after it, except as root.

That's what would happen if sudo prepended root's PATH to your PATH. But suppose sudo appended root's path to your PATH. If this was sudo's behavior, then you'd probably assume that if you can run a program (call it bar) when simulating an initial root login shell (sudo -i), you could also run it with sudo bar. But that assumption would be wrong, because there might be a different bar in your own (i.e., not root's) path.

Rather than sudo's behavior changing from one Ubuntu release to another, what probably happened was that your PATH changed. If you add /sbin, /usr/sbin, and /usr/local/sbin to your PATH, the problem will be solved. Unless you only want sbin in your PATH when running programs as root. In that case, I recommend posting a separate question about that (though one technique for accomplishing this is hinted at in Anders's answer.)

Ubuntu – Transmission daemon: permission denied even if debian-transmission has root group

Try this:

mkdir /your_path/progress
mkdir /your_path/completed
sudo usermod -a -G debian-transmission your_user
chgrp debian-transmission /your_path/progress
chgrp debian-transmission /your_path/completed
chmod 770 /your_path/progress
chmod 770 /your_path/completed
sudo service transmission-daemon stop
sudo adduser your_user debian-transmission
sudo nano /etc/init.d/transmission-daemon
sudo chown your_user -R /var/lib/transmission-daemon/info/
sudo chown your_user -R /your_path/progress
sudo chown your_user -R /your_path/completed
sudo chown your_user -R /etc/transmission-daemon/settings.json

And change in the file: sudo nano /etc/transmission-daemon/settings.json

"rpc-whitelist": "127.0.0.1" > "rpc-whitelist": "*.*.*.*",
"rpc-password": "password" > "rpc-password": "your_password",
"download-dir": "/var/lib/transmission-daemon/downloads" > "download-dir": "/your_path/completed"
"incomplete-dir": "/var/lib/transmission-daemon/downloads" > "incomplete-dir": "/your_path/progress"

Just restart the daemon:

service transmission-daemon start

Best Answer

Related Solutions

Ubuntu – Why does sudo not add root’s PATH with Ubuntu 12.04

Ubuntu – Transmission daemon: permission denied even if debian-transmission has root group

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