Along with Keychain, the FileVault on your Mac ensures that your files and folders are well protected. The trouble is when you accidentally forget your master password. If you mistype it three times, your Mac will be stuck at the master password login screen and display the error 'Type the master password to reset this user’s password and to unlock FileVault. Master Password hint: ...' You can try a full reboot to get all your settings back, but there is also another non-reboot solution to the problem. It's a bit more tricky, but worth it.
First thing, your locked Mac needs to be connected to another Mac via network, and ssh needs to be enabled. You also need to know the administrator name and password of the locked up Mac. From the unlocked Mac, determine the IP address of the locked-up Mac. You can do this by clicking the grey area under "Mac OS X" in the login window. Once you have it, open up the Terminal and type
ssh -l admin_name 188.8.131.52
admin_name is the name of the user on the locked up Mac and
184.108.40.206 is the IP address.
Enter the administrator password and press enter. Type in :
ps -aux | grep loginwindow.app and press Return. In the results you get, locate the Process ID (PID) for root's instance of login window. Type in sudo kill PID# (PID# being the number you just found). Enter your admin password and press Return. The login window will disappear and disappear. In the Terminal window of your unlocked Mac type in
logout to end your ssh session. You've unlocked your master password login screen without rebooting!