chgrp [-fhv] [-R [-H | -L | -P]] group file …

chgrp sets the group ID of file.

-f force, ignore errors, ( except for usage errors) and doesn't query about strange modes (unless the user does not have proper permissions).
-R Change the group ID for the file hierarchies rooted in the files instead of just the files themselves.
With -R: override each other and the last one specified is used.
  -RP symbolic links are prevented from being followed. default.
  -RL all symbolic links are followed.
  -RH symbolic links on the command are followed but not those encountered in the tree traversal
-h For symbolic link, the group ID of the link is changed not the target.
-v verbose, shows files as modified, non-standard and its use in scripts is not recommended.

group can be a group name or group ID.

The user invoking chgrp must belong to the group and be the owner of the file, or be the super-user.

Exits 0 on success, and >0 if an error occurs.

/etc/group group ID file

See chown, group, passwd, symlink, chown, ls, fts