Debian
View all failed login attempts
cat /var/log/auth.log | grep 'sshd.*Invalid'
View all successful logins
cat /var/log/auth.log | grep 'sshd.*opened'
RedHat/Centos
View all failed login attempts
cat /var/log/secure | grep 'sshd.*Invalid'
View all successful logins
cat /var/log/secure | grep 'sshd.*opened'
