Ubuntu – Need to use sudo with ssh

Could you run

sudo -s
id

And post the output? I want to see if it's actually making you the user you think.

Also, try

sudo cat /etc/sudoers

The output of id here is quite enlightening. When you ran sudo -s, you were given a UID of 1, while the only UID that the kernel will recognize as having root privileges is UID 0.

Try running

getent passwd | grep ':0:'

and see if any entries have that 0 in their first numeric field, the UID. Whatever account that is is the real superuser on the system, while root is a fake. Once you know the name, you can try

sudo -s -u username

to get a shell as that user.

You should also post the output of

getent passwd root

The bigger issue here is how such a condition came to pass.

Is this machine offering any network services? If so, someone may have broken into it and taken it over. In that case, you should probably back up the data, do a clean re-install, and audit anything that goes back on it.

If it's more of a personal machine, might there be a knowledgeable prankster who's had access to it recently?

Edit: your comment to another answer suggests that this is a server. I would highly recommend taking it offline ASAP and imaging its disks for forensic purposes. Unless you can identify a benign cause for this in short order, you've probably had your server cracked.

Don't use a password. Generate a passphrase-less SSH key and push it to your VM.

If you already have an SSH key, you can skip this step… Just hit Enter for the key and both passphrases:

$ ssh-keygen -t rsa -b 2048
Generating public/private rsa key pair.
Enter file in which to save the key (/home/username/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/username/.ssh/id_rsa.
Your public key has been saved in /home/username/.ssh/id_rsa.pub.

Copy your keys to the target server:

$ ssh-copy-id id@server
id@server's password:

Now try logging into the machine, with ssh 'id@server', and check-in:

.ssh/authorized_keys

Note: If you don't have .ssh dir and authorized_keys file, you need to create it first

to make sure we haven’t added extra keys that you weren’t expecting.

Finally, check to log in…

$ ssh id@server

id@server:~$

You may also want to look into using ssh-agent if you want to try keeping your keys protected with a passphrase.