passwd

Modify a user password.

SYNTAX
      passwd [options...] 

OPTIONS
   -d, --delete        delete the password for the named account (root only)

   -f, --force         force operation (effectively calls `chfn'?)

   -k, --keep-tokens   keep non-expired authentication tokens

   -l, --lock          lock the named account (root only)

   -S, --status        report password status on the named account (root only)

   --stdin             read new tokens from stdin (root only)

   -u, --unlock        unlock the named account (root only)

   -?, --help          Show this help message

   --usage             Display brief usage message

If no options are specified - passwd will change the password of the currently logged in user - will prompt for the old and new passwords.

Password aging (for new accounts) can be set to enforce a limited lifetime for each password: /etc/login.defs
parameters: PASS_MAX_DAYS, PASS_MIN_DAYS, PASS_WARN_AGE

"Chico : you can't come in unless you give the password...
Well, what is the password?... I got it! Haddock! ~ Groucho Marx

Related:

chgrp - Change group ownership
chage - Set password age
chmod - Change access permissions
chown - Change file owner and group
who - Print who is currently logged in
/etc/default/useradd
/etc/login.defs
Password generator
Equivalent Windows command: NET USER username * /domain