Ubuntu: Up and Running

Users and Groups

Each file has two additional attributes that are string values: one for the Owner and one for the Group the file belongs to. There is also a third attribute known as World (or sometimes Others) that is automatically assumed when a user is not in either of a file’s Owner or Group attributes.

In Figure 5-5, I have right-clicked the file rn.png and then selected the Permissions tab. In it you can see the Owner, Group, and Others sections, within which my username is applied to both the Owner and Group attributes. As Owner I am allowed to read from and write to the file, as a group member (if I were not the Owner) I could only read from it, and everyone else is also limited to only reading the file. A checkbox below this allows you to enable the file as executable.

Figure 5-5. Modifying a file’s permission settings

When you installed Ubuntu and it asked you for a username, it then went and gave your user account membership in a new group it also created, with the same name as your username. So, if your username is joesmith, you will also be a member of the group called joesmith. This is because you must be a member of at least one group. But you can also be a member of other groups.

For example, an Ubuntu multiuser installation might offer several different user accounts for accessing different parts of a company’s data. One group able to access the accounts might be called ...