AIX, Security, System Admin↑ Clearing password history

Sometimes when password rules are very strict, a user may have problems creating a new password that is both easy to remember, and still adheres to the password rules. To aid the user, it could be useful to clear the password history for his or her account, so he or she can re-use a certain password that has been used in the past. The password history is stored in /etc/security/pwdhist.pag and /etc/security/pwdhist.dir. The command you can use to disable the password history for a user is:

# chuser histsize=0 username

Actually, this command does not the password history in /etc/security/pwdhist.dir and /etc/security/pwdhist.pag, but only changes the setting of histsize for the account to zero, meaning, that a user is not checked again on re-using old passwords. After the user has changed his or her password, you may want to set it back again to the default value:

# grep -p ^default /etc/security/user | grep histsize
        histsize = 20
# chuser histsize=20 username

In older AIX levels, this functionality (to use chuser histsize=0) would actually have cleared out the password history of the user. In later AIX levels, this functionality has vanished.

So, if you truely wish to delete the password history for a user, here's another way to clear the password history on a system: It is accomplished by zeroing out the pwdhist.pag and pwdhist.dir files. However, this results in the deletion of all password history for all users on the system:

# cp /dev/null /etc/security/pwdhist.pag
# cp /dev/null /etc/security/pwdhist.dir

Please note that his is a temporary measure. Once these files are zeroed out, as soon as a user changes his or her password again, the old password is stored again in these files and it can't be reused (unless the histsize attribute for a user is set to 0).