Is the uid >= 500? On RHEL/CentOS, the default PAM config has a check for uid. Another possibility could be the password is expired (if you set it as root using passwd <username>) - does a login rather than su to the user reveal any issues there? Does it work using Pubkey authentication rather than a password?
The reason is probably logged in authlog, and troubleshooting without that log data is really just speculation.
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.
Best Answer
You should create the file /root/.ssh/environment on client2, assuming that /root is the home directory of root.