about sshd settings

ssh (secure shell)

- service name : sshd

- log file
/var/log/secure*
/var/log/audit/audit.log

- default configuration files and ssh ports
/etc/ssh/sshd_config     --> openssh server configuration file
/etc/ssh/ssh_config     --> openssh client configuration file
~/.ssh/     --> user ssh configuration directory
~/.ssh/authorized_keys    ---> lists public key (RSA or DSA) that can be used to log into the user's account
/etc/nologin     --> if the file exists, sshd refuses to let anyone except root log in
/etc/hosts.allow  
/etc/hosts.deny     --> these two file are access control list that should be enforced by tcp-wrappers defined here

- ssh default port    ---> tcp:22

- examples of using tcp wrappers for sshd
allow ssh only from 192.168.1.2 172.16.23.12
put the line in /etc/hosts.allow
sshd : 192.168.1.2 172.16.23.12
vsftpd : ALL

put the line in /etc/hosts.deny
ALL : ALL

- enable warning banner
put the line in /etc/ssh/sshd_config
Banner /etc/banner      (the file name banner must exists in /etc)