To make information available to all the nodes in the network, the DOMAIN system organizes objects in a hierarchical structure called a naming tree. The naming tree serves as a type of map that the sys-tem uses to keep track of where objects reside in the network. To access an object, you refer to its location in the naming tree. Figure 1-2 shows a sample naming tree.
Figure 1-2. A Sample Naming Tree
The double slashes (! /) in Figure 1-2 represent the top level of the naming tree, the network root directory. Each node maintains its own copy of the network root directory, which contains the name of each node entry directory the node can access. Figure 1-2 shows a
network root directory containing the names of two node entry direc-tories: NODE_B and NODE_C.
Each disked node in the network has a node entry directory name associated with it. This name refers to the branch of the naming tree that resides on its disk. (Since diskless nodes don't have disks, they
Entry directories contain one or more upper-level directories. An upper-level directory is one level below the entry directory and nor-mally serves as the main directory for a branch of logically related objects. For example, the /SYS directory that we supply is an upper-level directory that contains many of the system objects that make up the operating system. (Appendix A contains a set of figures that il-lustrate how the system organizes the software we supply with your node.) An upper-level directory can also serve as a user's main directory for storing files.
In Figure 1-2, the directories OWNER and USER_l are upper-level directories, one level below the entry directory NODE_B. The direc-tory OWNER serves as the main direcdirec-tory for all objects that belong net-work root directory to determine which node entry directories in the network it can access. Each node entry directory contains one or more upper-level directories. An upper-level directory serves as the main directory for logically related objects.
Your node can access only the node entry directories whose names appear in the local copy of the network root directory. To keep your local copy of the network root directory up to date, you should catalog new disked nodes as they are added to the network. To catalog new nodes, use the Shell command CTNODE
(CATALOG_NODE) described in the DOMAIN System Command Reference.
Some network sites use the NS_HELPER (Naming Server Helper) to maintain an up-to-date network root directory. If your site uses NS_HELPER, you don't need to use CTNODE to catalog nodes;
NS_HELPER does it for you. To find out if your network site uses the NS_HELPER, ask your system administrator. Administering Your DOMAIN System describes NS_HELPER and explains how to catalog nodes to update the network root directory.
The system identifies each object in the naming tree by its unique location. Whenever you specify a command to create or access an object, you also specify a pathname that points to the object's loca-tion in the naming tree. The pathname tells the system what path to follow when searching for an object.
The commands you use to create and manage objects require you to specify a pathname as a command argument. When you invoke a command, the command specifies the operation, and the pathname tells the system where in the naming tree to perform it.
For example, the following Shell command deletes the file MEMO in the naming tree shown in Figure 1-3 :
$ DLF command
T
IINODE_B/USER_1/MEMO I
pathname
The Shell command D LF (D ELETE_ FILE) tells the system to delete the file at the location specified by the pathname. Figure 1-3 shows the path the system follows to the file.
The pathname directs the system to:
1. Start at the network root directory (! /) .
2. Follow the path through the entry directory, NODEJj, and the subdirectory, USER_I.
3. Stop at the file, MEMO.
Figure 1-3. A Sample Path Through the Naming Tree When the system searches for a location in the naming tree, it begins its search at some point in the tree and follows a path to the location.
The pathname in the previous examples explicitly specified the net-work root directory as the starting point for the system's search through the naming tree. (The double slashes (! /) at the beginning of the pathname specify the network root directory.) This type of pathname, called an absolute pathname, tells the system the full path, from the network root directory to the final location.
You don't have to begin pathnames with the network root directory specification. For example, the single slash (I) symbol directs the system to begin its search at your node's entry directory. Here is an example using the single slash to start a search at your node's entry directory:
$
Figure 1-4. A Sample Path Beginning at the Node Entry Directory
For this example, let's assume that your node's entry directory is NODE B. As shown in Figure 1-4, the pathname directs the system to:
1. Start at your node's entry directory, NODE_B.
2. Follow the path through the upper-level directory, USER_i.
3. Stop at the file, MEMO.
You can specify other starting points in the naming tree by beginning a pathname with any of the symbols in Table 1-1.
Table 1-1. Pathname Symbols
Symbol System starts search at:
II
Network root directory/
N ode entry directoryNo symbol or • Working directory