-g     Interpret all operands as unsigned decimal integer process group IDs.

-n  increment
       Specify  how the nice value of the specified process or processes is to be adjusted. The increment
       option-argument is a positive or negative decimal integer that shall be used to  modify  the  nice
       value of the specified process or processes.

Positive  increment  values  shall  cause  a  lower  nice  value.  Negative  increment values may require
appropriate privileges and shall cause a higher nice value.

-p     Interpret all operands as unsigned decimal integer process IDs. The -p option is the default if no
       options are specified.

-u     Interpret  all operands as users. If a user exists with a user name equal to the operand, then the
       user ID of that user is used in further  processing.  Otherwise,  if  the  operand  represents  an
       unsigned decimal integer, it shall be used as the numeric user ID of the user.