The groupmod command modifies the system account files to reflect the changes that are specified on the command line. The options which apply to the groupmod command are
The numerical value of the group's ID. This value must be unique, unless the -o option is used. The value must be non-negative. Values between 0 and 99 are typically reserved for system groups. Any files which the old group ID is the file group ID must have the file group ID changed manually.