Sudo trouble cant su anymore

I somehow broke sudo on one of my systems and dont know how to fix it.
I looked with the visudo editor and did not find any change.

I tried fixing it by adding an admin group and adding a user to that group. Didnt resolve the problem either.

Anyone has an idea how to fix it?
All I get now is:

$ su
Password:
su: Authentication failure

Here is the visudo setup.
>
> #
> # This file MUST be edited with the ‘visudo’ command as root.
> #
> # Please consider adding local content in /etc/sudoers.d/ instead of
> # directly modifying this file.
> #
> # See the man page for details on how to write a sudoers file.
> #
> Defaults env_reset
> Defaults mail_badpass
> Defaults secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
>
> # Host alias specification
>
> # User alias specification
>
> # Cmnd alias specification
>
> # User privilege specification
> root ALL=(ALL:ALL) ALL
>
> # Members of the admin group may gain root privileges
> %admin ALL=(ALL) ALL
>
> # Allow members of group sudo to execute any command
> %sudo ALL=(ALL:ALL) ALL
>
> # See sudoers(5) for more information on “#include” directives:
>
> #includedir /etc/sudoers.d


I am not a fan of sudo at all and think the linux community was duped into believing it is safer for sysadmins. I disagree., but too many things now depend on it so I have to live with it.

su only works if you know root user password. In other words type root user password when you run:

su -

If you are in sudo group, run:

sudo command
sudo id
sudo reboot

I know but
If I su from a user account and enter root password I get

$ su
Password:
su: Authentication failure

but I can log into root without trouble using Ctrl Alt F1 e.g.

I dont know how this got messed up.

I cannot su to another user account either.

The culprit seems to have been the “MX User” application. It happened after I added another user with it.

It ended up being memory corruption. ECC error in a memory pair on that server.
I noticed it when I rebooted. Real Pesky problem this was.
Can you believe it.

Replaced the memory and this problem disappeared.

Nixcraft, I dont know if you want to delete the thread or if it will be useful for the group. It is your decission.

That is okay, someone might find it useful later.