It is a good idea to change your password every month or at least every four months. Make sure you use combination of alphabets (upper and lower case characters), numbers, and special characters as a password to safeguard your account. You should choose a password of at least ten characters. Do not write down your username and password. Do not share your password or send anyone via email, even if the email or sysadmin requesting your password seems official. A request for a password via email is very likely a phishing scam.
passwd command syntax
You need to use the Unix passwd command to change your password. The syntax is:
The Unix will prompt you for your old password, ask for a new password, and force you to repeat your new password for verification. Please note that Unix passwords are case sensitive. The above command will change the password only on the computer or server you are currently using. If you are logged on nas01 server the password will only on the nas01 sever and not on nas02 or any other Unix based server/computer.
For more information please see passwd command man page.