No matter which method you use to reset administrator password on mac, it won't automatically update the password protecting the account's login keychain. Since the keychain is still protected with the old administrator password, there would be no way to get back into it unless you could update keychain password or create new keychain.
The keychain services API helps you solve this problem by giving your app a mechanism to store small bits of user data in an encrypted database called a keychain. When you securely remember the password for them, you free the user to choose a complicated one. The keychain is not limited to passwords, as shown in Figure 1. An essential Mac OS X Keychain guide Troubleshooting and advanced Keychain Access tips Has your Mac suddenly started asking you for account and Wi-Fi passwords it never used to require?
Probably you are just prompted to do that at startup after Mac admin password reset, such as on Yosemite, or constantly asked to enter the keychain password after Mac login. Regardless of which happens, resetting keychain password would help you access Keychain again.
After you log into Mac with new administrator password, follow the steps below.
1. Open Keychain Access from Finder> Applications Utilities, and choose Keychain AccessPreferences from top menu.
2. In newer versions of Mac OS X, such as on Yosemite, you will see a button Reset My Default Keychain under the General pane.
3. Click it and enter the new login password in Password field to create new keychain.
Note: If you have no such button, choose EditKeychain List (Command + Option + L), select the login keychain, and click the minus button to delete it.
4. Quit Keychain Access and restart Mac. A new login keychain will recollecting and storing the passwords for Wi-Fi networks, email accounts, Web sites, and other logins as they occur.
If you cannot work with Keychain Access because of something like Messages Agent constantly asking for the forgotten login keychain password, you can use command line to reset Keychain password in single user mode.
1. Restart Mac and hold on Command + S to enter single user mode.
2. After you are prompted to enter a command-line after numerous lines of status messages, type this command to mount the root Mac OS X drive as writable.
mount -uw /
3. Delete that account's login keychain.
Tv shows for mac download. rm /Users/shortname/Library/Keychains/login.keychain
Note: If you are not sure the shortname, please confirm it with command 'ls /Users' at first.
4. Reboot Mac by command 'reboot'.
After Mac starts, you should have created a new keychain on Mac.
1. Click Update Keychain Password and enter the old password at startup, or continue login and enter old password when you are asked.
2. Open Keychain Access and right click on login, and choose the option Change Password for Keychain 'Login' from pop-up menu.
3. Enter the old password in 'Current Password' field and new password in 'New Password' box. Verify it and click OK to successfully change keychain password.