Here's the original source: OpenSSH Root user account restriction - revisited .
-- “I need something that allows me to say: allow any users except root from anywhere, and root only from localhost. (over ssh session)”.
PAM offers very powerful authentication control.
You need to use the pam_access PAM module, which is mainly for access management. It provides login access control based on Login names, Host or domain names, Internet addresses, or network IP numbers, Terminal line names etc.
Why pam_access matters?
On a production server, authorized login can come from any networked computer. Therefore, it is important to have tight control over users who are allowed to connect server via OpenSSH server.
How do I configure pam_access?
You need to edit following files:
/etc/pam.d/sshd - Linux PAM configuration file.
/etc/security/access.conf - By default rules for access management are taken from configuration this file. When someone logs in, the entry in this scanned and matched against rule. You can specify whether the login will be accepted or refused to user. General syntax is as follows:
permission : username: origins
permission : Permission field should be a “+” (access granted) or “-” (access denied)character.
username : Linux system username/login name such as root, yelei etc. You can also specify group names. You can also use special keywod ALL (to match all username).
origins : It is a list of one ore more tty names, host name, IP address, domain names that begin with . or special key words ALL or LOCAL Let us say you want to allow user root and yelei login from IP address 18.104.22.168 only.
Open file /etc/security/access.conf, and append following line:
-: ALL EXCEPT root yelei:22.214.171.124
Save the file and Open /etc/pam.d/sshd file, and append following entry:
account required pam_access.so
Save and close the file.