partition that it exports to the rest of the pack. However, this means all of your internal nodes will no longer be identically configured. The most common arrangement is for every node to have a full local copy of /usr, especially now that hard drive storage capacities are so large and the prices so low. A typical /usr partition will consume about 5% of a 10 GB hard drive.
6.4.3 Account Management
User account management is generally handled in one of two ways. The first is to assign an account to a user on the worldly node, and then copy the /etc/passwd file to every node. The second is to configure your internal nodes to use NIS or NIS+ for user authentication. This requires you to only configure accounts on the worldly node, which should be the home of the NIS server. Each method has advantages and disadvantages which we will mention shortly. In both cases, setting up the account on the worldly node works the same way. You can either use the useradd command, which supersedes the older adduser command (this may be a symbolic link to useradd on some systems), or one of the emerging Linux system administration tools such as linuxconf. These commands will create a home directory for the new user containing system default config files and will create an entry in /etc/passwd storing the user's encrypted password, home directory location, and shell.
After creating an account for a new user on the worldly node, you have to provide some means for the internal nodes to access the user data for authentication. The most commonly implemented method is to simply copy the /etc/passwd file to all the internal nodes, usually using one of rdist, rcp, or prsh. You will also have to replicate /etc/group which will have also changed with the addition of the new user. More often than not, several people will have account granting privileges on your system, so you have to make sure to avoid attempting simultaneous updates. This should not be a problem as long as you do not develop a habit of manually editing the password and group files. User accounts should be removed with either userdel or deluser and groups should be removed with groupdel. But you will also have to update the password and group files on the internal nodes the way you did when you added the user.
The alternative method of managing user accounts is to use a directory service, such as NIS, to store user account information. This makes system administration a lot easier, since you only have to worry about one point of control for account management. As discussed in Chapter 5, NIS stores all directory data in a central server, which is contacted by clients to perform authentication. This has the side-effect of generating extra network traffic every time you log in to a Beowulf node. The node must contact the server to verify you are a valid user and also check your
