Ubuntu – Cannot login as super user anymore

rootsudoUbuntu

I have an issue with login as root with in ubuntu.

I've mistakely assigning my user to a group as primary group and it is not anymore in sudoers.
Consequently I cannot use "sudo" anymore.

I tried to login as "root" but it doesn't accept the password. Or maybe, it has never been assigned.

So… am I screwed ?
Should I format the system and start over again ?

Best Answer

Assuming that you use Ubuntu, you can select the recovery entry in the Grub boot menu. This will boot the system into the single-user mode, which will give you full root access, and the possibility to add your user back to the sudo-group.

Related Solutions

Linux Sudo – How to Restore Sudo Privilege with Linux Live CD

You'll have to boot into recovery mode to gain root (system-wide) access in order to repair

If you have a single-boot (Ubuntu is the only operating system on your computer), to get the boot menu to show, you have to hold down the Shift key during bootup.

From the boot menu, select recovery mode

After you select recovery mode and wait for all the boot-up processes to finish, you'll be presented with a few options. In this case, you want the Drop to root shell prompt option.

/etc/group is the file that defines the groups on the system

You can then use adduser username admin to readd your user to the admin group.

Alternatively you can use the vigr command to edit the /etc/group file safely

format example;

group-name:x:group-number:user1,user2
admin:x:110:username

sudo Alerts – Fixing Annoying sudo Alerts Due to Defaults Entries

Solution

This problem is caused by sudo looking for directives in a place it cannot find them: sss. Check the /etc/nsswitch.conf file and modify the sudoers entry.

sudoers:        files sss

The sss should not be there. The sssd-ad package adds itself there, but very few environments store sudoers directives in sss. It’s far more likely your directives are local, so you should have a /etc/nsswitch file entry like the following:

sudoers:        files

References

A user of RHEL6 had the same issue. https://bugzilla.redhat.com/show_bug.cgi?id=879633
The issue is solvable, including on Ubuntu 16.04 https://bugs.launchpad.net/ubuntu/+source/sssd/+bug/1249777
https://bgstack15.wordpress.com/2016/06/06/solve-sudo-sending-useless-emails-problem-with-defaults-entries/