Group is a name service database used to store group information on Unix-like operating systems. The sources for the group database (and hence the sources for groups on a system) are configured, like other name service databases, in nsswitch.conf. The database file is located at /etc/group. It contains fields representing the group name, group id, encrypted password, and users belonging to the group. These fields are stored in a structure defined in the header file <grp.h>.
The contents of the group database (and available groups) can be seen with a variety of tools:
The <grp.h> header file contains the functions getgrgid and getgrname to look up a group by its ID or Name, as well as the functions setgrent, getgrent, and endgrent to iterate through all groups.[1]
The getent command can be used to fetch group information.
getent group
For a specific group called 'users':
getent group users