If option -s specified then changed only samba password. If options -u specified then changed only UNIX password. With no options then changed both - UNIX and samba passwords.
Password Changes The user is first prompted for their old password, if one is present. This password is then tested against the stored password by binding to the server. The user has only one chance to enter the correct passwword. The super user is permitted to bypass this step so that forgotten passwords may be changed. The user is then prompted for a replacement password. As a general guideline, passwords should consist of 6 to 8 characters including one or more from each of following sets:
Lower case alphabetics
Upper case alphabetics
Digits 0 thru 9
Password will prompt again and compare the second entry against the first. Both entries are require to match in order for the password to be changed.