HP OpenVMS Systems Documentation
OpenVMS Programming Concepts Manual
32.1.2 Logical Name Tables
A logical name table contains logical name and equivalence string pairs. Each table is an independent name space. When you translate a logical name, you specify the table containing the name. A logical name table is referred to by its name, which is itself a logical name, or by another logical name that translates into the table name.
Logical name tables can be created in process space or in system space. Tables created in process space are accessible only by that process. Tables created in system space are potentially shareable among many processes. OpenVMS creates a number of logical name tables with specific characteristics. These predefined logical name tables have names beginning with the prefix LNM$.
Logical name and equivalence name pairs are maintained in three types of logical name tables:
188.8.131.52 Logical Name Directory Tables
Because the names of logical name tables are logical names, table names must reside in logical name tables. Two special tables called directories exist for this purpose. Table names are translated from these logical name directory tables. Logical name and equivalence name pairs for logical name tables are maintained in the following two directory tables:
The process directory table contains the names of all process-private user-defined logical name tables created through the SYS$CRELNT system service. In addition, the process directory table contains system-assigned logical name table names and the name of the process logical name table LNM$PROCESS_TABLE.
The system directory table contains the names of potentially shareable logical name tables and system-assigned logical name table names. Typically, you must have the SYSPRV privilege to create a logical name in the system directory table. For a discussion of privileges, see Section 32.3.
Logical names other than logical name table names can exist within
these tables, but are strongly discouraged. The length of the logical
names and table names created in either of these tables must not exceed
31 characters. Logical table names and logical names created in the
directory tables must consist of uppercase alphanumeric characters,
dollar signs ($), and underscores (_). Equivalence strings must not
exceed 255 characters.
OpenVMS creates a number of logical name tables automatically, some at system initialization and some at process creation. Some of these tables are accessible to all processes, and some are accessible only to selected processes. These tables are called the default logical name tables.
Each default logical name table has a logical name associated with it in addition to its table name. The default logical name table names and the common logical names used to refer to them are as follows:
1The letter x represents a numeral in an 8-digit hexadecimal number that uniquely identifies the job logical name table.
2 The letter g represents a numeral in a 6-digit octal number that contains the user's group number.
The length of the logical names created in these tables cannot exceed
255 characters, with no restriction on the types of characters used.
Equivalence strings cannot exceed 255 characters. By convention, a
Compaq-created logical name begins with a facility-specific prefix,
followed by a dollar sign ($) and a name within that facility. You are
strongly encouraged to define logical names without the dollar sign ($)
to avoid inadvertent conflicts.
The process logical name table LNM$PROCESS_TABLE contains names used exclusively by the process. A process logical name table exists for each process in the system. Some entries in the process logical name table are made by system programs executing at more privileged access modes; these entries are qualified by the access mode from which the entry was made. The process logical name table contains the following process-permanent logical names:
SYS$COMMAND is created only for processes that execute LOGINOUT.
Usually, you create logical names only in your process logical name table. Most entries in the process logical name table are made in user or supervisor mode.
Process logical names that are created in user mode are deleted whenever the creating process runs an image down. The following DCL commands illustrate this behavior with supervisor mode and /TABLE=LNM$PROCESS as the defaults (default mode and default table) for the DEFINE command:
The DCL command DIRECTORY performs image rundown when it is finished
operating. At that time, all user-mode process-private logical names
are deleted, including the logical name ABC.
The job logical name table is a shareable table that is accessible by all processes within the same job tree. Whenever a detached process is created, a job logical name table is created for this process and for all of its potential subprocesses. At the same time, the process-private logical name LNM$JOB is created in the process directory logical name table LNM$PROCESS_DIRECTORY. The logical name LNM$JOB translates to the name of the job logical name table.
Because the job logical name table already exists for the main process, only the process-private logical name LNM$JOB is created when a subprocess is created.
The job logical name table contains the following three process-permanent logical names for processes that execute LOGINOUT:
Instead of creating these logical names within the process logical name table LNM$PROCESS_TABLE for every process within a job tree, LOGINOUT creates these logical names once when it is executed for the process at the root of the job tree.
Additionally, the job logical name table can contain the following logical names:
The group logical name table contains names that cooperating processes in the same group can use. You need the GRPNAM privilege to add or delete a logical name in the group logical name table. For a discussion of privileges, see Section 32.3.
A group logical name table is created when a top-level process with a
unique group code is created. The logical name LNM$GROUP exists in each
process's process directory LNM$PROCESS_DIRECTORY. This logical name
translates into the name of the group logical name table.
The system logical name table LNM$SYSTEM_TABLE contains names that all processes in the system can access. This table includes the default names for all system-assigned logical names. You need the SYSNAM or SYSPRV privilege to add or delete a logical name in the system logical name table. For a discussion of privileges, see Section 32.3.
The system logical table contains system-assigned logical names accessible to all processes in the system. For example, the logical names SYS$LIBRARY and SYS$SYSTEM provide logical names that all users can access to use the device and directory that contain system files.
The Logical Names section of the OpenVMS User's Manual contains a list of
these system-assigned logical names.
The clusterwide system logical name table LNM$SYSCLUSTER_TABLE contains names that all processes in the cluster can access. This is the clusterwide table that contains system logical names. Because this table exists on all systems, the programs and command procedures that use clusterwide logical names are transportable to both clustered and nonclustered systems. The names in this table are available to anyone translating a logical name using SHOW LOGICAL/SYSTEM and specifying a table name of LNM$SYSTEM, or LNM$DCL_LOGICAL (DCL's default table search list), or LNM$FILE_DEV (system and RMS default).
LNM$SYSCLUSTER is the logical name for LNM$SYSCLUSTER_TABLE. It is provided for convenience in referencing LNM$SYSCLUSTER_TABLE and it is consistent in format with LNM$SYSTEM_TABLE and its logical name, LNM$SYSTEM.
You need either the SYSNAM or SYSPRV privilege or write access to the table to create or delete a name in this table.
The definition of LNM$SYSTEM has been expanded to include LNM$SYSCLUSTER. When a system logical name is translated, the search order is LNM$SYSTEM_TABLE, LNM$SYSCLUSTER.
The clusterwide logical name table LNM$CLUSTER_TABLE is the parent table for all logical names, including LNM$SYSCLUSTER_TABLE. When you create a new table using LNM$CLUSTER_TABLE as the parent table, the new table will be available clusterwide.
LNM$CLUSTER is the logical name for LNM$CLUSTER_TABLE. It is provided for convenience in referencing LNM$CLUSTER_TABLE.
You need either the SYSPRV privilege or write access to the table to create or delete a name in this table.
Logical names in these two tables and their descendant tables are clusterwide. Creation and deletion of cluster wide logical names are replicated on other nodes of the cluster. Creation and deletion of clusterwide logical name tables are replicated on other nodes of the cluster. When a node boots into a cluster, it receives the current set of clusterwide logical names.
LNM$SYSCLUSTER_TABLE and LNM$CLUSTER_TABLE are created on all systems,
regardless of whether they are cluster nodes. Their existence enables
OpenVMS to maintain a consistent application environment.
The process, job, group, and system tables are typically referred to indirectly. For example, the process table is usually specified as LNM$PROCESS. This indirect reference enables you to redefine LNM$PROCESS as multiple equivalence names and thus include one or more of your own tables in it.
The system table is specified as LNM$SYSTEM. The logical name LNM$SYSTEM is defined as LNM$SYSTEM_TABLE, LNM$SYSCLUSTER. Thus, it includes both systemwide names specific to the node and systemwide names common to all nodes in the cluster. When a system name is translated, the search order is LNM$SYSTEM_TABLE, LNM$SYSCLUSTER.
As described in the OpenVMS User's Manual, OpenVMS automatically defines a number of logical names, some of which are names of logical name tables. In addition to the table names in the table in Section 184.108.40.206, OpenVMS defines LNM$FILE_DEV and LNM$DCL_LOGICAL.
RMS and other system components specify the table LNM$FILE_DEV for file specification and device name translations. Its definition is LNM$PROCESS, LNM$JOB, LNM$GROUP, LNM$SYSTEM. Thus, the precedence order for resolving logical names using this search list is as follows:
The table name LNM$DCL_LOGICAL is used for the SHOW LOGICAL and SHOW
TRANSLATION DCL commands and for the logical name lexical functions.
Its definition is LNM$FILE_DEV.
Logical names exist as entries within logical name tables. When a logical name is to be created, deleted, or translated, you must specify or take the default name that designates the logical name table that contains the logical name. This name possesses one or more of the following characteristics:
As mentioned in Section 32.1.2, predefined logical names exist for certain logical name tables. These predefined names begin with the prefix LNM$. You can redefine these names to modify the search order or the tables used.
Instead of a fixed set of logical name tables and a rigidly defined order (process, job, group, system) for searching those tables, you can specify which tables are to be searched and the order in which they are to be searched. Logical names in the directory tables are used to specify this searching order. By convention, each class of logical name (for example, device or file specification) uses a particular predefined name for this purpose.
For example, LNM$FILE_DEV is the logical name that defines the list of logical name tables used whenever file specifications or device names are translated by OpenVMS RMS or the I/O services. LNM$FILE_DEV is the default for file specifications and device names. This name must translate to a list of one or more logical name table names that specify the tables to be searched when translating file specifications.
By default, LNM$FILE_DEV specifies that the process, job, group, and system tables are all searched, in that order, and that the first match found is returned.
Logical name table names are translated from two tables: the process logical name directory table LNM$PROCESS_DIRECTORY and the system logical name directory table LNM$SYSTEM_DIRECTORY. The LNM$FILE_DEV logical name table must be defined in one of these tables.
Thus, if identical logical names exist in the process and group tables, the process table entry is found first, and the job and group tables are not searched. When the process logical name table is searched, the entries are searched in order of access mode, with user-mode entries matched first, supervisor-mode entries second, and so on.
If you want to change the list of tables used for device and file
specifications, you can redefine LNM$FILE_DEV in the process directory
You can create process-private tables and shareable tables by calling the SYS$CRELNT system service in a program, or with the DCL command CREATE/NAME_TABLE. However, to create a shareable table you must have create (C) access to the parent table and either SYSPRV privilege or write (W) access to LNM$SYSTEM_DIRECTORY. If granted access, processes other than the creating process can use shareable tables. For a discussion of privileges, see Section 32.3. Processes other than the creating process cannot use logical names contained in process-private tables.
You can assign protection to these shareable tables through the promsk argument of the SYS$CRELNT system service. The promsk argument allows you to specify the type of access for system, owner, group, and world users, as follows:
You can apply the following types of ownership and access to a shareable logical name table:
If the promsk argument is omitted, complete access is granted to system and owner, and no access is granted to group and world.
When a shareable table is created, both the specified promsk argument and the current default security profile for tables are applied.
In addition, you can specify finer-grained access rights by modifying the access control list using either the DCL command SET SECURITY or the SYS$SET_SECURITY system service. For more information, see Chapter 25 and OpenVMS Guide to System Security.
The length of logical names created in user-defined logical name tables
cannot exceed 255 characters. Equivalence strings cannot exceed 255
You might want to create additional clusterwide logical name tables for the following purposes:
You can create additional clusterwide logical name tables in the same way that you can create additional process, job, and group logical name tables---with the CREATE/NAME_TABLE command or with the $CRELNT system service. When creating a clusterwide logical name table, you must specify the /PARENT_TABLE qualifier and provide a value for the qualifier that is a clusterwide name. Any existing clusterwide table used as the parent table will make the new table clusterwide.
The following example shows how to create a clusterwide logical name table:
To create clusterwide logical names that will reside in the clusterwide logical name table you created, you define the new clusterwide logical name with the DEFINE command, specifying your new clusterwide table's name with the /TABLE qualifier, as shown in the following example:
32.3 Checking Access and Protection
When a user tries to access a logical name table, the operating system compares the security profile of the user with the security profile of the table. The operating system uses the following sequence:
The system checks the privileges in the user authorization file (UAF) granted to you when your system manager sets up your account. Privileges allow you to perform the functions listed in Table 32-2.
The system also checks for read, write, and delete access.
For example, a user without SYSPRV privilege but with write access to LNM$SYSTEM_DIRECTORY can create or delete a shareable table.