How to Lock and Unlock a User in Ubuntu Linux

1)
I have a user named "a1", and i can logging as user a1 using following command:

      praveen@praveen-VirtualBox:~$ su praveen
      Password: [enter the password]
     praveen@praveen-VirtualBox:/home/praveen$

2)
I am going to lock the user "praveen".

      praveen@praveen-VirtualBox:~$ sudo passwd -l praveen
      [sudo] password for praveen: [enter the password]
      passwd: password expiry information changed.
    praveen@praveen-VirtualBox:~$

3)
After i locked user "praveen",  I am trying to login as user "praveen" and it should fail.

       praveen@praveen-VirtualBox:~$ su praveen
      Password:
      su: Authentication failure
      praveen@praveen-VirtualBox:~$

     
4)
After that i unlocked the user "praveen" using following command.

  praveen@praveen-VirtualBox:~$ sudo passwd -u praveen
     passwd: password expiry information changed.
   praveen@praveen-VirtualBox:~$ 

5)
After unlock the user "praveen" i am going to logging as user "praveen" and it should  success.

     praveen@praveen-VirtualBox:~$ su praveen
      Password: [enter the password]
      praveen@praveen-VirtualBox:/home/praveen$