Java™ Application Development on Linux - Dator

446Chapter 20Open Source Web <strong>Application</strong> Servers(well, sudo lets you limit it, but a mistake can be fatal—consider what happensif you let them run a program that lets them escape to a shell). So, for example,if you want to let the Web services group install and maintain JBoss, but youdon’t want them to mess with any standard software on the system, then createa separate place for nonsystem software.Two common places for such software on Linux systems are /opt and/usr/local. We tend to use /usr/local mainly because this is the defaultpath on an awful lot of software that uses autoconf to handle cross-platformcompilation (it is used by the majority of Free Software programs, but exceptionsinclude what are arguably the four most widely used Free Software packages:the Linux kernel, the Apache Web server, the Perl language, andXFree86). So we are going to install JBoss under /usr/local and we are goingto give a number of users the power to install and manage software in/usr/local.You will need to be root to carry out this procedure. Here are thesteps—but don’t worry, we’ll pad them out with a lot of ponderousexplanation:1. Create the group.Groups are defined in the file /etc/group. Each line in that filedefines a group. Each line is of the form:GroupName:x:GroupID:GroupMembersGroupName is the name of the group. It is the group name that showsup in long form ls output. The second field is for the group’s password.If we may confess, we don’t know if this feature works anymore. You usedto be able to specify a group password, but this defeats the whole purposeof not sharing passwords. Sharing passwords is a security risk. Don’t doit. The third field is the group ID number. Remember that files haveowning users and owning groups. These are both stored as numbers. Usernumbers are known as uids and group numbers as gids. These numbersshould be unique. If you reuse a number for more than one group, theeffect could be indeterminate, since it would depend on how a given programwas written. Don’t reuse numbers. The final column is a commadelimitedlist of user names. Those named users are said to belong to thegroup. We’ll talk some more about what that means as we go on.