You can set the number of old passwords that are stored for each user.

1

Log in to the service console and acquire root privileges.

2

Change to the directory /etc/pam.d/.

3

Use a text editor to open the system-auth-generic file.

4

Locate the line that starts with password sufficient /lib/security/$ISA/pam_unix.so.

5

Add the following parameter to the end of the line, where X is the number of old passwords to store for each user.

remember=X

Use a space between parameters.

6

Save your changes and close the file.

7

Change to the directory /etc/security/ and use the following command to make a zero (0) length file with opasswd as the filename.

touch opasswd
8

Enter the following commands:

chmod 0600 opasswd 
chown root:root /etc/security/opasswd