You can change your password with the UNIX passwd command. passwd first asks you to type your old password, then asks for a new one. By asking you to type your old password first, passwd prevents somebody from walking up to a terminal that you left yourself logged into and then changing your password without your knowledge.
UNIX makes you type the password twice when you change it:
% passwd Changing password for sarah. Old password: tuna4fis New password: nosmis32 Retype new password: nosmis32 %
If the two passwords you type don't match, your password remains unchanged. This is a safety precaution: if you made a mistake typing the new password and UNIX only asked you once, then your password could be changed to some new value and you would have no way of knowing that value.
Even though passwords are not echoed when they are printed, the BACKSPACE or DELETE key (or whatever key you have bound to the "erase" function) will still delete the last character typed, so if you make a mistake, you can correct it.
After you have changed your password, your old password is no good. Do not forget your new password! If you forget your new password, you will need to have the system administrator set it to something you can use to log in and try again.
If your system administrator gives you a new password, immediately change it to something else that only you know! Otherwise, if your system administrator is in the habit of setting the same password for forgetful users, your account may be compromised by someone else who has had a temporary lapse of memory; see the following sidebar for an example.