$ apropos -a change password
    chage (1)            - change user password expiry information
    kpasswd (1)          - change a user's Kerberos password
    passwd (1)           - change user password
    PKCS12_newpass (3ssl) - change the password of a PKCS12 structure

    $ apropos -a space disk
    df (1)               - report file system disk space usage
    df (1p)              - report free disk space