Linux / UNIX SSHD: Find Out All Failed Login Attempts

Sshd (OpenSSH Server) which replace older rlogin and rsh / telnet, and provide secure encrypted communications between two untrusted hosts over an insecure network.However, OpenSSH is open to various password guessing attacks. Use the following commands to find out all failed login attempts:

a) Use the grep command to find out authentication failure message from /var/log/secure file.

b) Use the awk and cut command to print IPs/hostname.

c) Use the sort command to sort data.

d) Use the uniq command to print total failed login attempts.

Procedure

1) Login as the root user

2) Type the following command at shell prompt:

 grep "authentication failure" /var/log/secure | awk '{ print $13 }' | cut -b7-  | sort | uniq -c

Output:

 1 216.12.193.35
 2 DEVssh
 2 hack.baddomain.net
 ...
 ..

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