DESCRIPTION
       shadow manipulates the contents of the shadow password file, /etc/shadow. The
       structure in the #include file is:

       struct spwd {
             char          *sp_namp; /* user login name */
             char          *sp_pwdp; /* encrypted password */
             long int      sp_lstchg; /* last password change */
             long int      sp_min; /* days until change allowed. */
             long int      sp_max; /* days before change required */
             long int      sp_warn; /* days warning for expiration */
             long int      sp_inact; /* days before account inactive */
             long int      sp_expire; /* date when account expires */
             unsigned long int  sp_flag; /* reserved for future use */
       }

       The meanings of each field are:

       ·  sp_namp - pointer to null-terminated user name

       ·  sp_pwdp - pointer to null-terminated password

       ·  sp_lstchg - days since Jan 1, 1970 password was last changed

       ·  sp_min - days before which password may not be changed

       ·  sp_max - days after which password must be changed

       ·  sp_warn - days before password is to expire that user is warned of pending
          password expiration

       ·  sp_inact - days after password expires that account is considered inactive and
          disabled

       ·  sp_expire - days since Jan 1, 1970 when account will be disabled

       ·  sp_flag - reserved for future use