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Adding a group is simply a matter of clicking the Manage Groups button in the Users and Groups program window (System Administration Users and Groups). After clicking the Add button, you ll be prompted to give the group a name. The GID will be filled in for you automatically, but you could choose a different number if you have good reason to do so. (Remember to use a number above 1,000 to keep in line with the way Ubuntu operates.) It isn t essential that you add users to the group then and there, but a list of users is provided at the bottom of the dialog box. Put a check alongside any user to grant that user access to your group.

Note Bear in mind that users can be members of more than one group, although all users have a main group that they belong to, from which the GID is assigned to files they create.

The interesting thing about hard links is that there is no difference between the original file and the link: they are just two names connected to the same inode. The disadvantage of using them is that hard links must exist on the same device, which is rather limiting. But, if possible, you should always create a hard link instead of a symbolic link because they are faster.

Let s recall some relational calculus from the previous chapter. Our questions about who did or did not enter Open tournaments can be conveniently represented with calculus expressions. This approach allows us to answer the questions involving negatives that we had trouble with in the previous section. Let s start with a simple question. For example: What are the names of all members who have ever entered any tournament We can start by thinking in terms of which rows of the Member table would satisfy our question. Consider the following sentence and Figure 4-4 together: I ll write out the names from row m, where m comes from the Member table, if there exists a row e in the Entry table where m.MemberID = e.MemberID. Listing 4-9 shows the equivalent calculus expression.

As with user accounts, deleting a group is simply a matter of highlighting it in the list and clicking the Delete button. You should ensure that the group no longer has any members before doing this,

because Ubuntu won t prevent you from removing a group that has members (although it will warn you that this is a bad thing to do).

At the beginning of this chapter, you learned how to perform some of the most common file system management tasks. However, there s more to managing storage on your server. In 1, you saw how to install your server using LVM and how to use different file systems for your server. I will now go into more depth with regard to these subjects. First, differences between file system types will be discussed in depth. Then you will learn about the creation of file systems, which involves creating and formatting partitions and logical volumes. Next, you can read how to set up a software RAID solution.

Note Ubuntu appears to offer protection against the havoc caused by deleting a group that is the main group of users on your system. When we deleted an entry that was the main group of a different user and then logged in as that user, the group was automatically re-created! You shouldn t rely on this kind of protection, however, and should always check before deleting a group.

Listing 4-9. Relational Calculus Expression to Retrieve Members Who Have Entered a Tournament {m.LastName, m.FirstName | Member(m) and (e) Entry(e) and m.MemberID = e.MemberID}

Used for system logging Required for use of serial port devices, such as older modems Allows the user to access the CD/DVD-ROM Allows the user access to removable storage, such as card readers, digital cameras, and so on Allows the user to administer the printer Gives the user system administration abilities (superuser powers) Facilitates sharing files with others across the network

Listing 2-2. The history Command Shows a List of All Commands That You Recently Used. sander@RNA:~$ history 1 clear 2 dpkg -l "*" | grep ^un 3 aptitude search xen 4 aptitude show xen-source

As you might have guessed, to manually add a user under Ubuntu, not only must you create a group and then add the user to it, but you must also add that user to the required selection of supplementary groups. Some are considered mandatory for effective use of the computer, such as plugdev, while others are optional, depending on how much freedom you want to afford the new user.

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