sudo -s works but su does not in ubuntu?

Question

I have Linux Virtual machine (ubuntu 12.04) installed on my Mac OS.

On my terminal,

[email protected]:~$ su
password:
su : Authentication failure

[email protected]:~$ ls -lth /bin/su
-rwsr-sr-x 1 root root 36K Sep 12 2012 /bin/su

But the following works:

[email protected]:~$ sudo ls
[sudo] password for user:
(....lists the directories)

 [email protected]:~$ sudo -s
 [sudo] password for user:
 [email protected]:~#

Hence the question is, why sudo -s works and logs in as root, while su results in authentication failure. I typed the passwords correctly each time. Also sudo ls works

possible duplicate of su command + authentication failure – Eliah Kagan Aug 08 '14 at 23:29 — Eliah Kagan, Aug 08 '14 at 23:29

score 2 · Accepted Answer · answered Aug 08 '14 at 21:53

2

In Ubuntu by default, the root user has a disabled password and the mechanism available for general users to use root permissions is sudo. su with no arguments attempts to change the current user to root, and since it is disabled....

answered Aug 08 '14 at 21:53

Charles Green

21,339

well it prompts for password su and when I type in the correct password, it gives authentication failure – brain storm Aug 08 '14 at 21:55
Exactly. "su" will still prompt for a password, but since the root account is disabled, you get authentication failure. "sudo" depends upon your username having sudo permissions. – Charles Green Aug 08 '14 at 21:58
but I have seen where su and followed by password works. If this feature is possible, how to enable it? or how to undo the disable of root account? – brain storm Aug 08 '14 at 22:00
@brainstorm: see this question. – saiarcot895 Aug 08 '14 at 22:39

score 2 · Answer 2 · answered Aug 08 '14 at 22:25

2

I think you can do what you are looking for using:

sudo su

This works for me on Ubuntu 14.04. Although in general you should be careful about doing this for security reasons.

answered Aug 08 '14 at 22:25

TheSchwa

3,820

score 1 · Answer 3 · answered Aug 08 '14 at 23:23

1

try using

    sudo passwd root

to change password for your su user. See if that helps. Then retry using su and entering the password you have have have just assinged.

answered Aug 08 '14 at 23:23

Vyras

21

score 0 · Answer 4 · edited Mar 18 '15 at 09:32

0

sudo -i

gives a root prompt,

passwd

changes the root password, from that point you can login as usual.

edited Mar 18 '15 at 09:32

Jens Erat

5,051
7
31
37

answered Mar 17 '15 at 10:34

ArrantSymmetry

1

sudo -s works but su does not in ubuntu?

4 Answers4