Hi, welcome to LQ!
I have created 2 users and changed their secondary group to grp1, then changed permission for a directory dir1 to 770(no permission for others) and group to grp1.
The both normal users are not able to access dir1. How is it possible to access that Dir using general permission (770).
And that depends on the permissions on the parent directory/directories.
Should any of those not be readable/accessible by grp1 the grp1 directory
won't be, either.