I want to verify that the user account filesender_1 is a member of the group valid_senders.
When I look at /etc/group, filesender_1 is not there:
I read this as "production_1 is the only member of the group valid_senders, whose group id is 12345."
When I look at /etc/passwd, the group id for valid_senders is listed for filesender_1 ...
... so I know valid_senders is the primary group for filesender_1.
Is this a surprising discrepancy, or is it normal for /etc/group to list only members where the group is secondary?