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Fedora20 su login authentication failure

asked 2016-02-28 06:19:30 -0600

jadesword gravatar image

No matter what password I use, the result is the same.

$ su --login
Password:
su: Authentication failure
$

Is there a default password or is there a command that is required to enable and set a password for su?

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answered 2016-02-28 08:15:30 -0600

jadesword gravatar image

Found the answer at {http://askubuntu.com/questions/168101/why-cant-i-access-super-user-mode-with-su} and it worked.

$ sudo passwd -S root
root PS 1969-12-30 0 99999 7 -1 (Password set, SHA512 crypt.)
$ sudo passwd root
Changing password for user root.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
$ sudo passwd -S root
root PS 2016-02-27 0 99999 7 -1 (Password set, SHA512 crypt.)
$ su --login
Password:
Last failed login: Sun Feb 28 05:58:49 MST 2016 on pts/1
There were 5 failed login attempts since the last successful login.
#

The date of the original password is interesting as it seems that the su default password was set by the original programmer.

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answered 2016-02-28 07:55:49 -0600

robyduck gravatar image

I think you're mixing up some things here. su stands for switch user and is used to switch from one to any other user of the system, like su jerry. If you do not specify any user, you are going to switch to the root or administrator. So the password it is asking for is the root or administrator password.

Anyway, reading your answers you probably didn't set your root user as separate user during te installation process, but just used your user account with administration privileges (your user is part of the wheel group). Therefor you do not have a password for root but need to use sudo following by the command you want to execute, like sudo dnf update.

Note: you can still create a root user as admin if you like, you don't need to do that only during installation.

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answered 2016-02-28 06:59:47 -0600

su does not have a password by itself as it just used to change the current UID. By default su changes to the root account, so you should enter the password of the root account in your example.

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As stated, I tried several passwords, the account password should have worked, but failed. Every other guess failed as well. Further research says that I should change the permissions using chmod, but I am not sure of the exact coding as there are no examples of the format in the documentation. One suggestion is [sudo chmod -v 7777 /bin/su", but I have yet to try it.

jadesword gravatar imagejadesword ( 2016-02-28 07:09:13 -0600 )edit

You normally do not have to change the permissions on su. What do you mean with account password? User account? When running su without a user name, then it will ask for the root password.

thomaswood gravatar imagethomaswood ( 2016-02-28 07:15:44 -0600 )edit

What is the "root" password?

jadesword gravatar imagejadesword ( 2016-02-28 07:34:11 -0600 )edit

You set it during installation.

thomaswood gravatar imagethomaswood ( 2016-02-28 07:47:51 -0600 )edit

You are correct about the permissions. Without the correct password, no permission change would have worked. I was just poking around when I ran across the actual solution that worked and I do not need the default root password that was entered by the original programmer. I am learning.

jadesword gravatar imagejadesword ( 2016-02-28 08:28:32 -0600 )edit

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Asked: 2016-02-28 06:19:30 -0600

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Last updated: Feb 28 '16