Who, and with Whom?
Charly's Column – User Groups
This time Charly investigates the three most frequently asked questions about user groups.
Most people know that every user on a Linux system is also a member of at least one user group. Today we want to look into the three most frequently asked questions about groups: Which groups exist, how many members does a group have and who are those members, and to what groups does a specific user belong?
First off, let's find out which groups exist on our system. There are several ways to do this. One of them is to use the groups command without further parameters; another one is provided by compgen -g. The getent group (Listing 1, line 1) and cat /etc/group commands also return the same result, with some additional information, including the group password. There is usually an x here, which means that /etc/gshadow takes care of that. This is followed by the numeric group ID and a comma-separated list of members.
The next thing is to find out which members belong to a group. In principle, we have already done this, because the getent group and cat /etc/group commands provide this information as well.
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