PRovides a dynamically managed firewall that supports groups of rules called zones
firewalld
The command-line client for firewalld
firewall-cmd
Pre-defined zones
drop
block
public
external
internal
dmz
work
homw
trusted
Open SSH SSH daemon config file
sshd_config
This keywork can be followed by a list of username patterns separated by spaces. If specific login is allowe only for usernames that match one of the patterns
AllowUsers
This keyword can be followed by a list of group name patterns separated by spaces. If specifed login is allowed only for users whose primary group or supplementary group list matches one of the patterns
AllowGroups